Wang Zhou-Xiang   Xie Yu-Chen   Huang Shuang-Yin   Zhou Han   Liu Rui   Liu Zhi-Feng   Wang Min   Qi Wen-Rong   Tian Qian-Qian   Kong Ling-Jun   Tu Chenghou   Li Yongnan   Wang Huitian  

      摘要 + 此论文可免费阅读 (可能需要登录)

In free-space or in optical fibers, the orbital angular momentum (OAM) multiplexing for information transmission has been greatly developed. The light sources used were well coherent communication bands and the fibers used were customized. Here we use an 810-nm femtosecond laser to generate optical vortices carrying OAM, and then feed them into two kinds of commercial step-index few-mode fibers to explore the transmission characteristics of OAM modes. We also propose a method without multiple-input multiple-output digital signal processing to identify the input OAMs. It is of great guiding significance for high-dimensional quantum information experiments via the OAMs as a degree of freedom, using the light generated by the spontaneous parametric down-conversion as source and the commercial fibers for information transmission.

       PDF全文        Chinese Optics Letters ，2019年第17卷第12期 pp.12      

Gu Fuxing   ubaid saima   Liao Feng   Tao Guo   Qi Zhao   Linghu Shuangyi   Ma Yanna   Yu Jiaxin  

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We demonstrate an effective approach of mode suppression by simply using a tungsten probe to destroy the external neck surface of polymer microbottle resonators. The higher-order bottle modes with large axial orders, spatially located around the neck surface of the microresonator, will suffer large optical losses. Thus, excitation just with an ordinary free-space light beam will ensure direct generation of single fundamental bottle mode lasers. This method is very low cost and convenient, and can obtain high side mode suppression factors. Our work demonstrated here may have promising applications such as lasing and sensing devices.

       PDF全文        Chinese Optics Letters ，2019年第17卷第12期 pp.12      

Cui Yuan   Zheng Guoxing   Chen Ming   Zhang Yilun   Yang Yan   Tao Jin   Li Zile  

      摘要 + 此论文可免费阅读 (可能需要登录)

Design of a conventional zoom lens is always challengeable because it requires not only sophisticated optical design strategy, but also complex and precise mechanical structures for lens adjustment. Here, we propose a continuous-zoom lens consisting of two chiral geometric metasurfaces with dielectric nanobrick arrays sitting on a transparent substrate. The metalens can continuously vary the focal length by rotating either of the two metasurfaces along its optical axis without changing any other conditions. Because of the polarization dependence of the geometric metasurface, the positive and negative polarities are interchangeable in one identical metalens only by changing the handedness of the incident circularly polarized light, which can generate varying focal lengths ranging from −∞ to +∞ in principle.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Dong Jia-ning   Fan Jie   Mao Si-da   Lan Yun-ping   Zou Yonggang   Wang Hai-zhu   Zhang Jia-bin   Ma Xiaohui  

      摘要 + 此论文可免费阅读 (可能需要登录)

The effect of thermal annealing on the optical properties, microstructure and laser-induced damage threshold (LIDT) of HfO2/Ta2O5/SiO2 HR films have been investigated. The transmission spectra shift to short wavelength and the x-ray diffraction (XRD) diffraction peaks of monoclinic structure HfO2 are enhanced after thermal annealing. The calculated results of m(-111) diffraction peak show that HfO2 grain size is increased, which is conducive to increasing the thermal conductivity. The thermal annealing also reduces the laser absorption of HR films. The improvement of thermal conductivity and the decrease of laser absorption both contribute to the improvement of LIDT. The experimental results show that the highest LIDT of 22.4J/cm2 is obtained at 300℃ annealing temperature. With the further increase of annealing temperature, the damage mechanism of the film changes from thermal stress damage to thermal explosion damage, resulting in the decrease of LIDT

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Li Xiang   wang xiaodan   Ma Hai   Chen Feifei   Zeng Xionghui  

      摘要 + 此论文可免费阅读 (可能需要登录)

In this work, Er doped AlN, Pr doped AlN, and Er, Pr co-doped AlN thin films were prepared by ion implantation. After annealing, the luminescence properties were investigated by cathodoluminescence. Some new and interesting phenomena were observed. The peak at 480 nm was observed only for Er doped AlN. However, for Er, Pr co-doped AlN, it disappeared. At the same time, a new peak at 494 nm was observed, although it was not observed for Er-doped AlN or Pr-doped AlN before. Therefore, the energy transfer mechanism between Er3+ and Pr3+ in AlN thin films were investigated in detail. Through optimizing the dose ratio of Er3+ with respect to Pr3+, white light emission with CIE chromaticity coordinate (0.332, 0.332) was obtained. This work may provide a new strategy for realizing white light emission based on nitride semiconductors.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Fang Fang   Sun Bing   Zhang Zuxing   Xu Jing   Zhang Lin  

      摘要 + 此论文可免费阅读 (可能需要登录)

The spectral characteristics and sensitivities of a tapered two-mode fiber (TTMF) sandwiched between two single-mode fibers (SMFs) are systematically proposed. Theoretical calculations reveal that a dispersion turning point (DTP) appears when the group effective refractive index (RI) difference between the fundamental mode and the higher-order mode equals zero, as a result, ultrahigh RI sensitivities can be achieved. Furthermore, the location of the DTP is strongly dependent on the tapering condition. Then we experimentally demonstrate high sensitivities of the RI sensor with the waist diameter of 2.4 μm by means of immersing it in a flow cell filled with glycerol solution. Further tracking the resonant wavelength shift around the DTP it is found that the proposed RI sensor exhibits a sensitivity of 1.81×104 nm/RIU and a limits of detection down up to 3.29×10-5 RIU in glycerol solution.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Wang Mingjun   Feng Shaodong   Wu Jigang  

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We propose a resolution enhancement method for lensless in-line holographic microscope (LIHM) by combining the hologram segmentation and pixel super-resolution (PSR) techniques. Our method is suitable for imaging specific target object in samples where the in-line hologram is disturbed by other objects in the samples. The resolution-enhancement capability of our method was proved by numerical simulations and imaging experiments while using a standard resolution target in a two-layer setup. We also applied our LIHM system to image the sample of living algae Euglena gracilis in water solution for further demonstration.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Ma Qungang   Cao Liangcai   He Zehao   Zhang Shengdong  

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In this paper, the principle and the optical methods for light-field display are introduced. The light-field display is divided into three categories, including layer-based method, projector-based method, and integral imaging method. The principle, characteristic, history and advanced research results of each method are also reviewed. The advantages of light-field display are discussed by comparing with other display technologies including binocular stereoscopic display, volumetric 3D display and holographic display.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Liu xin   Lei Ruoshan   Huang feifei   Deng Degang   Wang Huanping   Zhao shilong   Xu Shiqing  

      摘要 + 此论文可免费阅读 (可能需要登录)

BaMoO4: Ho3+/Yb3+ phosphors with different concentrations were fabricated by a gel combustion method. The upconversion (UC) luminescence, intrinsic optical bistability (IOB) and the corresponding mechanisms were reported for the present system. The optical thermometric properties based on the red (5F5 →5I8) and green (5F4/5S2 →5I8) emissions were studied. The sensing sensitivities could be tuned by manipulating the cooperative energy transfer (CET) process. The highest absolute sensitivity was 99 ×10-4 K-1 at 573 K, which was larger than many previous UC materials.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Othman Nurulanati   Tay Kim Gaik   Mohd Shah Nor Shahida   Talib Rahmat   Pakarzadeh Hassan   Cholan Noran Azizan  

      摘要 + 此论文可免费阅读 (可能需要登录)

The influence of the fourth-order dispersion coefficient on behavior of parametric gain and saturation power of one-pump fiber optical parametric amplifier over a signal wavelength span in presence of fiber random dispersion fluctuations was investigated. The output signal power for the parametric gain calculation was obtained by numerically solving the three-coupled amplitude equations. Based on the calculations of the parametric gain over a variation of the signal wavelength, it is found that the saturation power behavior is dependent on the behavior of parametric gain. The manipulations of signal wavelength and fourth-order dispersion coefficient changed the phase-matching condition, thereby affecting the resulting parametric gain and saturation power.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Guo Ying   Wang Kangshuai   Jiang Xueqin   Huang Duan  

      摘要 + 此论文可免费阅读 (可能需要登录)

Seeking for good error correcting codes to improve the efficiency of continuous-variable quantum key distribution (CVQKD) reconciliation is a concerned issue. Due to the introduction of multidimensional reconciliation, the error correcting techniques in the classical binary-input additive white gaussian noise (BI)-AWGN channel is applicable to CVQKD. In this letter, we apply the quasi-cyclic low-density paritycheck (QC-LDPC) codes, which are specified in 5G protocol, to the reconciliation process. Simulation results show that the reconciliation efficiency can reach 92.6% when the code rate is 22/68 and the signal-to-noise ratio (SNR) is 0.623. Such a new error correcting code points out a new direction for the development of CVQKD.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Gao Qian   Zhang Hengli   Javed Fayyaz  

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A laser diode partially end-pumped, electro-optic Q-switched, Yb:YAG slab laser was reported. We obtained an output energy of 14.6 mJ/pulse with a pulse width of 30 ns at a repetition frequency of 2 kHz, and the corresponding peak power was 480 kW. The beam quality factors M2 in the unstable direction and the stable direction were 1.32 and 1.25, respectively.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Wang Qiangguo   Cui Na   Yao Yongping   Meng Lihua   Li Lei   Dong Lulu   Zhang Huiyun   Liu Shande   Li Dehua  

      摘要 + 此论文可免费阅读 (可能需要登录)

With a Nd:ScYSiO₅ crystal, a high peak power electro-optically Q-switched 1.0 μm laser and tri-wavelength laser operations at 1.3 μm band are both investigated. With RTP electro-optical switcher and a polarization beam splitter, a high signal-to-noise ratio 1.0 μm laser is obtained, generating the shortest pulse width of 30 ns, the highest pulse energy of 0.75 mJ, and the maximum peak power of 25.5 kW, respectively. The laser mode at the highest laser energy level is TEM₀₀ mode with the M² value in X and Y directions to be M_x²=1.52 and M_y²=1.54. Besides, a tri-wavelength Nd:ScYSiO₅ crystal laser at 1.3 μm is also investigated. A maximum tri-wavelength output power is 1.03 W under the absorbed pump power of 7 W, corresponding to a slope efficiency of 14.8%. The properties of the output wavelength are fully studied under different absorbed pump power.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

刘 贺言   Yu yongji   sun dehui   Liu Hong   Wang yuheng   Zheng hao   Li dan   Jin Guangyong  

      摘要 + 此论文可免费阅读 (可能需要登录)

We report on a 1514nm eye-safe passively Q-switched self-optical parametric oscillator (SOPO). The nonlinear crystal is a a-cut Nd:MgO:PPLN crystal and the size of the crystal was 6 mm × 2 mm ×30 mm with 0.4at.% Nd3+ doped, grating period was 29.8μm.When the crystal absorbed 12.8W, the output maximum single pulse energy reached 39μJ and the pulse width of 6.1ns at a 5.4 kHz repetition rate was obtained, peak power is 6kw and giving a slope efficiency of 42%.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Wei Wei   Huang Lihua   zhu Xinran   ling liqing   Guo Kai   Huang Huijie  

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In our paper two kinds of handwriting traces, colored and colorless, are studied by means of Reflectance Transformation Imaging (RTI).The illumination direction and rendering mode can be changed alternatively to obtain two-dimensional and three-dimensional details of the traces that are not viewed easily by the naked eye. Furthemore, an objective evaluation method without reference is applied to evaluate the reconstructed images, which provides a basis for setting the illumination direction and rendering mode. Therefore, the information of handwriting traces including the written content, the writing features, and the stroke order features can be obtained objectively and accurately.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Wang Xiaoyan   Yan Xiaona   Jin Kailong   Dai Ye   Jin Zuanming   Yang Xihua   Ma Guohong  

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Based on Kogelnik’s coupled-wave theory, it is found that when a femtosecond pulse incidents on transmitted volume holographic grating, two transverse standing waves along grating vector direction will be generated inside the VHG. Due to field localization of two standing waves, they have two different velocities along propagation depth. On the output plane of the VHG, femtosecond dual pulses are generated on both the diffracted and transmitted directions. Results show that the pulse interval is determined by the refractive index modulation and thickness of the grating, while the waveform of the dual pulses is independent of grating parameters.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Cai Yuancheng   Gao Xiang   Ling Yun   Xu Bo   Qiu Kun  

      摘要 + 此论文可免费阅读 (可能需要登录)

A pre-coding-assisted power detection scheme for radio over fiber downlink is presented. This scheme can eliminate laser phase noise, while avoiding high energy-consuming electrical carrier required in conventional power and/or envelope detection scheme. Theoretical analysis and experimental verification are performed. 0.625 Gbaud pre-coded quadrature phase shift keying or 16 quadrature amplitude modulation signals can both be recovered by power detec-tion without electrical carrier assistance at the receiver after 75 km fiber transmission. Not only robust against the laser phase noise, an improvement of about 5 dB in receiver sensitivity can also be achieved, as compared with the conventional power detection scheme.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Xiong Ling   Qi Erhui   Luo Xiao   Zhang Feng   Xue Donglin   Zhang Xuejun  

      摘要 + 此论文可免费阅读 (可能需要登录)

We implemented a stitching swing arm profilometer (SSAP) test for inner and outer region of a large aspheric surface with a short arm. The SSAP was more capable of improving sampling density of surface, and was less sensitive to system error, like vibration noise, air-table noise. Firstly, a calculation model was built to evaluate the sampling density of the SSAP test. Then sensitivity to system noise was tested when different length of arm was used. At the end, an experiment on a 3m diameter aspheric was implemented, where test efficiency was promoted and high sampling density was achieved.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Wang Huan   Guo Lu   Wu Zhao   Chen Guangcan   Lu Dan   Zhao Lingjuan  

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We report a distributed-Bragg-reflectors-based 4 × 40 GHz mode-locked laser diode (MLLD) array monolithically integrated with an MMI combiner. The laser produces 2.98-ps pulses with a time-bandwidth product of 0.39. The peak wavelength of the MLLD array can be tuned by 8.4 nm while maintaining a good mode-locked state. The four mode-locked channels could work simultaneously with the peak wavelength interval around 3 nm.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Wang Mengyu   Yang Yu   Meng Lingjun   Jin Xueying   Dong Yongchao   Zhang Lei   Xu Wenbin   Wang Keyi  

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In this paper, we demonstrate high-Q, millimeter-size, and V-shaped calcium fluoride crystalline resonators for modal modification. To manufacture such resonators, we develop a home-made machining system and explore a detailed process. With a dedicated polished container, three special polishing steps, including grinding, smoothing, and polishing, are employed to achieve the required surface smoothness, which is characterized by less than 3 nm. An ultra-high Q-factor exceed 108 is obtained by a coupled tapered fiber. In addition, a customized packaged structure for our disk resonator is achieved. The Q maintenance and stable spectrum are realized by sealing the coupling system in a hard disk. The simple, stable, portable, controlled and integratable device would provide great potential in optical filters, sensors, nonlinear optics, cavity quantum electrodynamics and especially some applications that require large resonators such as gyroscopes.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

Cai Hao   Yu Xingtao   Chu Qian   Jin Zhiqiang   Lin Bo   Wang Guanghui  

      摘要 + 此论文可免费阅读 (可能需要登录)

A metal-lined hollow-core fiber based Raman probe extension kit is proposed in this paper for in Situ and sensitive ultramicro-analysis. Hollow-core fiber can confine light and fluid sample in its hollow core, with enhanced light-sample interaction. By using a homemade light coupling device with a glass window for liquid isolation, a 3.5 cm-long hollow-core fiber could mount on and connect to a Raman probe, with perfect light coupling efficient. After full filling the hollow-core fiber chamber with volume of 13 µL by using a syringe pump, it can act as an extension kit for ordinary Raman probe and could be used as ultramicro-analysis tool for the sample of microfluidic chips. In order to enhance its sensitivity, a gold film coated fiber tip is inserted into the capillary, which can double the Raman signal received by reflecting pump light and Raman light. Finally, a good sensitivity of detection limit of 5% for ethanol solution and an enhancement factor of 2 comparing with direct detection of bulk sample volume are demonstrated. Above all, our device can be utilized as a Raman probe extension kit, which is suitable for rapid, sensitive and in Situ measurements for few µL sample.

       PDF全文        Chinese Optics Letters ，2019年第17卷第11期 pp.11      

huang wei   cui yulong   Zhou Zhiyue   Li zhixian   Chen Yubin   Wang Zefeng  

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We report here a diode-pumped pulsed mid-infrared laser source based on gas-filled hollow-core fibers (HCFs) towards all-fiber structure by tapering method. The pump laser is coupled into an acetylene-filled HCF through a tapered single-mode fiber. By precisely tuning the wavelength of the diode to match different absorption lines of acetylene near 1.5 μm, mid-infrared emission around 3.1~3.2 μm is generated. With 2 m HCFs and 3 mbar acetylene gas, a maximum average power of 130 mW is obtained with a laser slope efficiency of ~24%. This work provides a potential scheme for all-fiber mid-infrared fiber gas lasers.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Lu Zhiyong   Lu Wei   Zhou Yu   Sun Jianfeng   Xu Qian   wang lijuan  

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A scanning three-dimensional coherent ladar based on the frequency modulated continuous wave (FMCW) is proposed and demonstrated, which can obtain many three-dimensional high-quality images. The system utilizes an electro-optic modulator and an optical filter to output a linear frequency modulated continuous waveform with a bandwidth of 2GHz. The flexible and variable rotating double prism is used for beam scanning. The images of flight demonstration are formed by attitude compensation correction. The experiment result validates the performance of our system for airborne three-dimensional scanning imaging.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Zhang Li   Lin Fei   qiu xiaodong   Chen Lixiang  

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We demonstrate the full vectorial feature of second-harmonic generation (SHG), i.e., from infrared full Poincaré beams to visible full Poincaré beams, based on two cascading type-I phase-matching BBO crystals of orthogonal optical axes. We visualize the structured features of vectorial SHG wave by using Stokes polarimetry and show the interesting doubling effect of polarization topological index, i.e., a low-order full Poincaré beam is converted to a high-order one. However, the polarization singularities of both C-points and L-lines are found to keep invariant during the SHG process. Our scheme could offer a deeper understanding on the interaction of vectorial light fields with media and can be generalized to other nonlinear optical effects

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

zhou xiong   Wang Hui   Xia Haiping   Song Hongwei   Chen Xu   Hu jianxu   chen baojiu  

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Yb³⁺/Er³⁺ co-doped Na₅Lu₉F₃₂ single crystals used as a spectral upconverter to improve the power conversion efficiency of perovskite solar cells are prepared via an improved Bridgman approach. Green and red upconversion (UC) emissions under the excitation of near-infrared (NIR) bands of 900-1000 nm and 1400-1600 nm can be observed. The effectiveness of the prepared materials as spectral converter is verified by the enhancement of power conversion efficiency of perovskite solar cells. Sample with UC layer is 15.5% more efficient to convert sunlight to electricity comparing to the UC layer-free sample due to the absorption of sunlight in the NIR range. The results suggest the synthesized Yb³⁺/Er³⁺ co-doped Na₅Lu₉F₃₂ single crystals are suitable for enhancing the performance of perovskite solar cells.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Zhang Xiaotong   Yang Shitai   Yuan Libo  

      摘要 + 此论文可免费阅读 (可能需要登录)

By using a specialty designed optical fiber, a series of powerful microparticle manipulation tools including optical tweezers, a micro-optical hand and an optical gun are developed and demonstrated. In this paper, a review of our research activities on the optical manipulation of microparticles will be presented. In particular, we will describe a kind of specialty optical fiber designed and fabricated for building optical trapping and manipulating tools. The performance of annular core fiber based optical tweezers, a multicore, fiber-based micro-optical hand and a coaxial dual waveguide fiber-based optical gun are demonstrated as examples of applications and discussed in detail. The fiber can be used in cell manipulation in life science and drug response in medicine.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Yang Xin   Wei Shibiao   Kou Shanshan   Yuan Fei   Cheng En  

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The misalignment of optical vortex (OV) beams, including transversal displacement and tilt, occurs in many situations, including on reflection or refraction at an interface between two different media and in propagation and tracking systems for optical communications. We propose a reliable method to determine and subsequently eliminate tilt and transversal displacement in an OV beam. An experimental setup was established to verify the proposed method and the experimental results showed good agreement with those of the numerical simulations. Using the measured misalignments, the initial orbital angular momentum spectrum can be recovered in free space.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Miao Shuaijie   Zhang Wentao   Song Ying  

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A new structure of short-cavity random fiber laser (RFL) with narrow linewidth lasing is proposed. A π-phase-shifted fiber Bragg grating (π-FBG) loop mirror was used in the RFL to spectral filtering and suppress multi-mode oscillation due to the narrow transmission window. The random feedback of the RFL was implemented by a randomly dispersed weak reflection FBG array. The high gain of the erbium-doped fiber and a half-open cavity design result in a low lasing threshold. The linewidth of the laser was 225 Hz with 58 dB side-mode-suppression-ratio. The laser threshold was 4.5 mW and the optical signal-to-noise ratio was up to 63 dB.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Liu Zhentao   Shen Xia   Liu Honglin   Yu Hong   Han Shensheng  

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The resolution of a conventional imaging system based on first-order field correlation can be directly obtained from the optical transfer function. However, it is challenging to determine the resolution of an imaging system through random media, including imaging through scattering media and imaging through randomly inhomogeneous media, since the point-to-point correspondence between the object and the image plane in these systems cannot be established by the first-order field correlation anymore. In this paper, from the perspective of ghost imaging, we demonstrate for the first time to our knowledge that the point-to-point correspondence in these imaging systems can be quantitatively recovered from the second-order correlation of light fields, and the imaging capability, such as resolution, of such imaging schemes can thus be derived by analyzing second-order correlation of the optical transfer function. Based on this theoretical analysis, we propose a lensless Wiener-Khinchin telescope based on second-order spatial autocorrelation of thermal light, which can acquire the image of an object by a snapshot via using a spatial random phase modulator. As an incoherent imaging approach illuminated by thermal light, lensless Wiener-Khinchin telescope can be applied in many fields such as X-ray astronomical observations.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Liu Xinyang   Li Xiaowen   Zhao Shengzhi   Yang Kejian   Guo Lei   Li Tao   Qiao Wenchao   Li Ming   Zhang Baitao   He Jingliang   Zheng Lihe   Su Liangbi   Xu Jun  

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A dual-wavelength synchronously mode-locked homogeneously broadened bulk laser operating at 1985.6 nm and 1989 nm is presented for the first time, to the best of our knowledge, which delivers a maximum output power of 166 mW and a repetition rate of 85 MHz. The pulse duration was measured to be 16.8 ps by assuming a Sech2 pulse shape. The recorded autocorrelation trace showed frequency beating signals with an interval of 3.8 ps and a FWHM duration of 2 ps, corresponding to an ultrahigh beating frequency of about 0.26 THz, which agrees well with the frequency difference of the emitted two spectral peaks. The results indicated that such a kind of dual-wavelength mode-locked Tm:YAP laser could be potentially used for generating terahertz radiations.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Chen Zhidong   Sang Xinzhu   Li Hui   Wang Yuan   Zhao Linmin  

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A novel see-through virtual retina display (VRD) system is proposed in this letter. An optical fiber projector is used as the thin-light-beam source, which is modified from a laser scan projector by separating the laser sources and the scan mechanical structure. A synthetic aperture method is proposed for simple, low-cost fabrication of a volume holographic lens with large numerical aperture. These two key performance-enhanced elements are integrated into a lightweight and ordinary-glasses-like optical see-through VRD system. The proposed VRD system achieves a weight of 30 grams and a diagonal field of view of 60.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Li Yuepeng   Cai Yawen   Li Runmin   Shi Haosen   Tian Haochen   He Mingzhao   Song Youjian   Hu Minglie  

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We demonstrate a robust femtosecond LIDAR setup by using two free running environmentally stable all polarization-maintaining (PM) nonlinear amplified loop mirror mode-locked fiber lasers. Based on asynchronous optical sampling (ASOPS) method, a ranging accuracy of ±2 μm within 65m has been achieved, as tested in an 80-meter long underground optical tunnel. Through Kalman filter in the real-time data processing, the measurement accuracy can be maintained at a 200 Hz update rate. This setup provides a practical tool for various large scale industrial and astronomical ranging applications.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Gan Haiyong   He Yingwei   Liu Xiangliang   Xu Nan   Wu Houping   Feng Guojin   Liu Wende   Lin Yandong  

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An absolute cryogenic radiometer (ACR) with a detachable optical window was designed and built for high accuracy optical radiant power measurement and photodetector spectral responsivity calibration. The ACR receiver is an electroplated pure copper cavity with a 50-μm-thick wall and inner surface coated with a specular black polymer material mixed with highly dispersible carbon nanotubes. The absorptivity of the cavity receivers was evaluated to be ≥0.9999 in 250 nm ~16 μm wavelength range and ≥0.99995 in 500 nm ~16 μm. The cavity receiver works at the temperature of ~5.2 K with nW-level noise-equivalent-power. The relative standard uncertainty is 0.041% for the measurement of ~100 μW optical radiant power (250 nm ~ 16 μm) and 0.015% for ~1 mW (500 nm ~ 16 μm).

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Deng Yuting   Jin Guofan   Zhu Jun  

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Freeform surfaces are difficult to manufacture due to their lack of rotational symmetry. To reduce the requirements for manufacturing precision, a design method is proposed for freeform reflective-imaging systems with low surface-figure-error sensitivity. The method considers both the surface-figure-error sensitivity and optical specifications, which can design initial systems insensitive to surface figure errors. Design starts with an initial planar system; the surface-figure-error sensitivity of the system is reduced during the construction. The proposed method and another which is irrelevant to figure-error sensitivity are used to design a freeform off-axis three-mirror imaging system. Comparison of the sensitivities of the two systems indicates the superiority of our proposed method.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Wang Xin   Yang Sihua  

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In this study, the feasibility of visualization of human joints using photoacoustic tomography (PAT) is investigated. To verify this idea, the system of integrated optical fiber bundles and custom-made flexible transducer is established, both of which give the advantage of morphological adaptation, therefore, the coupling section can be worn on human limbs. The imaging capacity of the flexible-transducer-based PAT system is validated by mapping the structures of the finger and the wrist joint. To our knowledge, it is the first time to achieve photoacoustic imaging of such a large human wrist joints. The cross-sectional photoacoustic images of a healthy joint clearly exhibit main internal structures including phalanx, tendons and blood vessels, which are comparable with the corresponding 3.0 T MRI images. The experimental results demonstrate that the proposed system holds promise for early diagnosis of joint disorders.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Zhou Xingye   Tan Xin   Wang Yuangang   Song Xubo   Han Tingting   Li Jia   Lu Weili   Gu Guodong   Liang Shixiong   Lv Yuanjie   Feng Zhihong  

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Ultroviolet (UV) detectors with large photosensitive area are more advantageous in low-level UV detection applications. In this letter, high-performance 4H-SiC p-i-n avalanche photodiodes (APDs) with large active area (800 µm diameter) are reported. With the optimized epitaxial structure and device fabrication process, a high multiplication gain of 1.4×10⁶ is obtained for the devices at room temperature, and the dark current is as low as ~10 pA at low reverse voltages. In addition, a record external quantum efficiency (QE) of 85.5% @ 274 nm is achieved, which is the highest value for the reported SiC APDs. Furthermore, the rejection ratio of UV to visible light reaches about 10⁴. The excellent performance of our devices indicates a tremendous improvement for large-area SiC APD-based UV detectors. Finally, the UV imaging performance of our fabricated 4H-SiC p-i-n APDs is also demonstrated for system-level applications.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Zhang Kui   Wang Zhengwei   Chen Guodong   Wang Yang   zeng Aijun   Zhu Jing   Avakaw Syarhei   Tsikhanchuk Heorgi  

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A Te-free binary phase change material SbBi is used as a new inorganic photoresist for laser heat-mode lithography. It shows good film-forming ability, low threshold power for crystallization, and enough etching selectivity. Line-type, dot-type, and complex pattern structures with the smallest feature size of 275 nm are fabricated on SbBi thin films using a laser direct writing system. In addition, the excellent grating structures with a period of 0.8 m demonstrate that thermal interference does not affect the adjacent microstructures obviously. These results indicate that SbBi is a promising laser heat-mode resist material for micro/nanostructure fabrication.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Luo Xiaoqing   Tan Zhi-Yong   Wang Chang   Cao Juncheng  

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We propose and experimentally demonstrate a wideband linear polarization converter in reflection mode operating from 2.4 to 4.2 THz with conversion efficiency more than 80%. Our device can expand the applications to a higher frequency band. A numerical simulation was performed for this metamaterial converter, which showed a good agreement with experimental results. Importantly, a concise and intuitive calculating model is proposed for the Fabry-Pérot cavity. The theoretical results indicate that the underlying reason for the enhanced polarization conversion is the additional phase difference induced by the resonance of meta-structure and multiple reflections within the Fabry-Pérot cavity.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Yang Baodong   Zhang Jinfang   Wang Junmin  

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An experimental investigation of two-color polarization spectroscopy (TCPS) is presented based on the cesium 6S1/2 - 6P3/2 - 8S1/2 (852.3 nm + 794.6 nm) ladder-type system in a room-temperature vapor cell. The dependency of lineshapes of TCPS on the power of 852.3 nm pump and 794.6 nm probe laser are measured in detail, and we confirm that the linewidth of TCPS in counter-propagating configuration between the pump and probe laser beams is obviously narrower than that of co-propagating configuration due to atomic coherence effect. It is helpful for laser stabilization to excited state transition using TCPS without frequency modulation.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Xie Youpeng   Lei Ting   Yang Chuanwu   Du Luping   Yuan Xiao-Cong (Larry)  

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Digital micro-mirror device (DMD)-based optical switch has the advantages of high-speed channels reallocation, miniaturization, stability and large capacity for short reach optical communication in Datacenter. However, the thermal turbulent atmosphere in Datacenter would cause perturbations and channel crosstalk for the optical switch. The self-healing optical beams such as the Bessel beams have the non-diffraction property to mitigate the turbulence issue. Here, we propose and demonstrate Bessel beams enabled DMD-based optical switch to improve the stability and performance of the optical communication in turbulent atmosphere. We statistically characterize the beam wanders of the Gaussian beams and Bessel beams in turbulent atmosphere at the temperatures of 60oC and 80oC. We built the two channels optical switch communication system and measure the bit error rate of the 15Gbit/s OOK signals transmitted by the Gaussian beams and Bessel beams at the temperatures of 60℃ and 80℃, respectively. The optical switch using the Bessel beams shows lower bit error rates with weaker fluctuations compared with the Gaussian beams. The DMD-based optical switch using the Bessel beams has the potential for practical optical communication applications in Datacenter.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Wang Xin-wen   Liu Kangkang   Cheng He-nan   ren wei   xiang jingfeng   Ji Jing-wei   Peng Xiang-kai   Zhang Zhen   zhao jianbo   ye meifeng   Li Lin   Li Tang   wang bin   qu qiuzhi   Liu Liang   lü desheng  

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A high-performance transportable fountain clock is attractive for use in laboratories with high-precision time-frequency measurement requirements. This letter reports the improvement on stability of a transportable rubidium-87 fountain clock because of an optimization of temperature characteristic. This clock integrates its physical packaging, optical benches, microwave frequency synthesizers and electronic controls onto an easily movable wheeled plate. Two optical benches with high vibration resistance is realized in this work. No additional adjustment is required after several times movement of them. The Allan deviation of the fountain clock frequency was measured by comparing it with that of the hydrogen maser. The fountain clock got a short-term stability of 2.3×10⁻¹³@1s and long-term stability to the order of 10⁻¹⁶@100000s

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Kong Qian   Zhan Yafeng   Wan Peng  

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We report on a DCN architecture based on hybrid Optical Circuit Switching (OCS) and Optical Burst Switching (OBS) interconnect for dynamic DCN connectivity provisioning. With the combination of the centralized and distributed control of the Software Defined Optical Networks (SDON), the proposed interconnect can achieve unprecedented flexibility in dealing with both mice and elephant flow in the DCN. Numerical simulation is employed to investigate the performance of the proposed architecture. The results show that OBS module has preferable performance in dealing with larger burst packet, and the throughput is constrained by the capacity of the server Random Access Memory (RAM) module.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Cen Yuan   Xie Jianlan   Liu Jianjun  

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In this Letter, a photonic crystal (PC) flat lens with scatterer-size-gradient is proposed, which simultaneously achieve imaging of point source and sub-wavelength focusing of plane wave in the first, the second and the fifth bands. The imaging of point source breaks through the diffraction limit in the second and the fifth bands. The PC flat lens with scatterer-size-gradient is expected to be used to new multifunctional optical imaging and focusing device, which improves the application potential of PC flat lens.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Gao Xin-Xia   Cui Jin-Ming   Huang Yunfeng   Li Chuanfeng   Guo Guangcan  

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We have demonstrated a mode matching method between two different fibers by a hybrid thermal expanded core (TEC) technique, which can be applied to match the modes of fiber-based Fabry-P\'erot cavities (FFPCs). Experimentally, this method has achieved an expansion of the ultraviolet fiber core by 3.5 times while keeping fundamental mode propagation. With the experiment parameters, the fundamental mode coupling efficiency between the fiber and micro-cavity can reach 95% for a plano-concave cavity with a length of 400 \mum. This method can not only have potential in quantum photonics research, but also can be applied in classical optical fields.

       PDF全文        Chinese Optics Letters ，2019年第17卷第9期 pp.09      

Xia Renjie   Wang Changshun   Chen Tianyu   Pan Yujia   Lyu Ziyao   Sun Lili  

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In this paper, an all-optical logic sequence generator based on two different polarization holographic gratings has been proposed and demonstrated, which has one input port and four output ports. The polarization state of input light signal determines logic output signals. It can produce four kinds of logic sequence output signals: 1000, 0100, 0010, and 0001, corresponding to the input light signal of four different polarization states: the p-linear, s-linear, left-handed circular, and right-handed circular. The two polarization gratings have been recorded and the working principle of the logic sequence generator has been proved by diffraction pattern analysis of polarization gratings.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Xue Jinxing   Liu Candong   Zeng Zhinan   Li Ruxin   Xu ZhiZhan  

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We theoretically investigate delay-dependent attosecond transient absorption spectra in the helium atom dressed by an infrared laser pulse in the wavelength range of 800–2400 nm. By numerically solving the three-dimensional time-dependent Schrödinger equation, we find that the absorption spectrogram exhibits a multiple-fringe structure for using the longer-wavelength dressing pulse. The quantitative calculation of the transition matrix between different Floquet states provides direct evidence on the origin of the multiple-fringe structure. Our result shows that the wavelength of the dressing pulse is an important parameter and the unique feature of attosecond transient absorption spectroscopy can be induced in the mid-infrared regime.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Wang Guoyan   Jiang Lan   Sun Jingya   Hu Jie   Wang Qingsong   Li Ming   Lu Yongfeng  

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Cylindrical shockwave inside PMMA generated simultaneously with two hemispherical shockwaves induced by femtosecond Gaussian beam laser was investigated using ultrafast pump-probe imaging technique. The evolutions of these three shockwaves with probe delay and incident pulse number have been systematically analyzed. The plasma intensity and filament length in the center of cylindrical shockwave both decayed with pulse number. Moreover, the self-focused filament moved downstream towards the output surface with increased pulse number. The experimental results and mechanism illustrated that energy deposition was suppressed by degraded nonlinear effect due to pre-ablated structure in multi-pulses irradiation.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Li Yingyi   Yang Ke   Liu Gaoyou   Yao Baoquan   Ju Youlun  

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We demonstrate a Fe:ZnSe laser gain-switched by a ZnGeP₂ (ZGP) optical parametric oscillator (OPO) under the pulse repetition frequency (PRF) of 1 kHz at room temperature. The 2.9 μm signal light of the OPO is employed as the pump for the Fe:ZnSe laser. The maximum output power of the Fe:ZnSe laser is 58 mW with the pulse duration of 2.7 ns under the incident pump power of 280 mW, corresponding to a peak pulse power of 21.5 kW and an optical-to-optical efficiency of 20.7%. The spectrum of the Fe:ZnSe laser has a range of 4030.2-4593.6 nm with a dip in 4187.1-4340.4 nm due to the absorption of CO₂.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Ji Jianhua   Zhang Jianjia   Wu Bing   Wang Ke   Xu Ming  

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We experimentally demonstrate a 10 Gb/s FSO wiretap channel based on spatial diversity scheme and optical code division multiple access (OCDMA). In weak and middle turbulence cases, bit error rate of legitimate user can be decreased and physical layer security can be enhanced simultaneously.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

He Xiaopeng   Huang Panhui   Yang Xiaoyu   Jin Zuanming   Lou shitao   Zhang Xiaolei   Jin Qingyuan  

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The ultrafast spin dynamic of in-plane magnetized Fe/Pt films was investigated by terahertz emission spectroscopy. The amplitude of emitted terahertz wave is proportional to the intensity of the exciting laser beams. Both the amplitude and polarity of the terahertz wave can be adjusted by modifying the external magnetic field. The dependency of the amplitude on external magnetic fields is coincidence to the hysteresis loops of the sample. Also the polarity of terahertz wave is reversed as the magnetization orientation is reversed. The superdiffusive transient spin current with inverse spin Hall effect (ISHE) is attributed to main mechanism of the terahertz emission.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Wang Xiaojing   Ren Huaijin   Wang Gang   He Jun  

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In this article, a new method is presented to calculate the interactive length between fundamental wave (FW) and second harmonic generation (SHG) for the configuration of total internal reflection on the inner surface of nonlinear crystal. Three independent experiments are designed to measure bandwidths of this second harmonic wave. The theoretical expression of the intensity of SHG is obtained through nonlinear coupled wave equation. By utilizing the measured bandwidths and the intensity equation through mathematical calculation, the interactive length of this phase-matched SHG can be calculated. Because there is no existing method to obtain the interactive length either from the theoretical calculation or experimental measurement. This method can be applied to estimate the extremely short interactive volume in nonlinear processes.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Huang Junchao   Wang Lingke   Duan Yifei   Huang Yafeng   ye meifeng   Li Lin   Liu Liang   Li Tang  

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Excess frequency noise induced by mechanical vibration is the dominant noise source at low Fourier frequencies in fiber-delay-line (FDL) stabilized lasers. To resolve this problem, a double-winding fiber spool is designed and implemented that has ultralow acceleration sensitivity in all spatial directions. By carefully choosing the optimal geometry parameters of the fiber spool, we achieve acceleration sensitivity of 8 × 10−11/g and 3 × 10−11/g in axial and radial directions, respectively.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Liu xiaojuan   Hu Ping   Huang Yan   Liu Fangfang   Liu Ying   Guo Liping   Ge Xiaolu  

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A passively Q-switched erbium-doped fiber laser is proposed and demonstrated utilizing a Zirconium Disulfide (ZrS2)-based saturable absorber. ZrS2 nanosheets are prepared whose modulation depth, saturation intensity and nonsaturable absorbance are measured to be 14.7%, 0.34 MW/cm2 and 17.4%, respectively. Then, a Q-switched EDF laser is implemented by the ZrS2-SA. The pulse repetition rate varies from 40.65 kHz to 87.1 kHz when the pump power changes from 55 mW to 345 mW. The shortest pulse width is 1.49 μs with pulse energy of 33.5 nJ. As far as we know, this is the shortest pulse width obtained by ZrS2-SA so far.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Fu Shiyao   Zhai Yanwang   Zhou Heng   Zhang Jianqiang   Yin Ci   Gao Chunqing  

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Multi-ring optical vortices are a kind of structured beams that carry orbital angular momentum (OAM) and have concentrical doughnut intensity distributions. In this paper, we present both theoretically and experimentally a scheme that employing the dimensions of both the OAM states and radial index of multi-ring optical vortices simultaneously to accomplish high-dimensional free-space data coding/decoding transmissions. Such scheme can further improve the coding efficiency when limited OAM states are available. In the proof-of-concept experiment, 64-ary coding/decoding employing 16 OAM states and 4 radial indices are present. And the coding/decoding performance when facing various atmosphere turbulence is evaluated. Furthermore, a 64×64 gray image (totally 32768 bits) is also transmitted through multi-ring optical vortices coding in free-space successfully, showing good transmission performance.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

tellal azeddine   ziane omar   Baldeck Patrice  

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The diffraction of a dielectric microline pair is optimized by numerical simulations to generate an efficient focusing pattern with a micron-scale footprint. Microlines separated by 1.12 µm are fabricated by two-photon polymerization on a glass substrate, and their diffraction pattern is characterized by 3D wide-field transmission microscopy. A line pair, having a width W = 0.4 µm and a height H = 0.8 µm, leads to a diffraction-limited focusing in the visible spectrum. Depending on wavelength, its focal length, lateral resolution, and depth of focus are in the ranges of 0.8-1.3 µm, 0.22-0.44 µm, and 1.7-2.13 µm, respectively. Such microlens based on the diffraction of only two subwavelength scatterers could be used for the design of miniature optical sensors with micron and sub-micron pixels.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

KOIRALA ISHWOR   Park Chul-Soon   Lee Sang-Shin   Choi Duk-Yong  

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Angle tolerant transmissive subtractive color filters incorporating a metasurface exploiting hydrogenated amorphous silicon (a-Si:H) nanopillars (NPs) on a glass substrate, were proposed and demonstrated. The achieved transmission efficiency ranged from 75% to 95% at off-resonance wavelengths. For NP resonator, electric and magnetic field distributions in conjunction with absorption cross-sections were investigated to confirm resonant transmission dip which is primarily governed by the absorption resulting from simultaneous excitation of magnetic and electric dipoles via Mie scattering. The proposed devices exhibit higher angular tolerance and lower crosstalk for the absorption spectra and therefore be applicable with photodetectors, image sensors, and imaging/display devices.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Che Abd Rashid Nurfatihah   Ngajikin Nor Hafizah   Azmi Asrul Izam   Arsat Rashidah   Isaak Suhaila   Cholan Noran Azizan   Azmi Nur Ellina  

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Spectrophotometer with LED being the light source for uric acid detection is proposed in this work. The mechanism of the uric acid detection is based on energy absorbed by sodium urate, which is a chemical product of uric acid and sodium hydroxide (NaOH) solution. For the performance validation, comparison between the spectrophotometer with LED and halogen lamp is carried out. Measurement results suggest that spectrophotometer system with LED light has better sensitivity than that with halogen light. At 460 nm wavelength, the sensitivity for the spectrophotometer with LED is 0.0046 dL/mg, which is 73% higher than that with halogen light that records 0.0012 dL/mg. This enhanced sensitivity is attributed to the higher luminous efficacy of the LED light beam. As a result, a larger amount of flux interacts with the sample, leading to the sensitivity enhancement. The spectrophotometer with LED is also applied for detection of uric acid in real human urine sample. Based on the experimental data at 460 nm wavelength, the method manages to achieve the sensitivity of 0.0016 dL/mg, accuracy of 96.01%, limit of detection (LOD) of 4.79 mg/dL and limit of quantification (LOQ) of 14.52 mg/dL. These findings show that the use of LED as the input light is promising for the spectrophotometer.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Xie Yafeng   Zhang Saifeng   Zhang Xiaoyan   Dong Ningning   Kislyakov Ivan   Luo Song   Chen Zhanghai   Nunzi Jean-Michel   Zhang Long   Wang Jun  

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Mechanically exfoliated (ME) and chemical vapor deposition (CVD) MoS₂ monolayers have been extensively studied, but the large differences of nonlinear optical performance between them have never been clarified. Here, we prepared MoS₂ monolayers using ME and CVD methods and investigated the two-photon absorption (TPA) response and its saturation. We found TPA coefficient of ME monolayer was about (1.88±0.21)×10³ cm/GW, nearly two times of CVD one, (1.04±0.15)×10³ cm/GW. Furthermore, we simulated and compared the TPA-induced optical pulse modulation in multilayer cascaded structures, which is instructive and meaningful for the design of optical devices such as beam shaper, optical limiter.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Guan Yan   Wang Fang   Yang Ying   Wang De'en   Zhang Xin   Qiang Yuan   Zhou Wei   Hu Dongxia   Deng Xuewei   Ren Huaijin  

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Collinear phase-matching of sum-frequency generation (SFG) has been studied thoroughly previously, while non-collinear schemes are sometimes more flexible in application. However, this phase-matching type is more difficult to meet and control. We employ a convenient method to obtain harmonic generation in bulk KDP: using an incident wave vector and a reflected wave vector to consist triangle phase-matching relationship. With a simple, flexible set-up, we can observe 351nm SFG and the conversion efficiency is up to ~3.6% per reflection. Furthermore, we believe this approach has potential application value and improvement space.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

li qin   Li Wenbo   Chu Wei   Cao Yuxiang   Zhang Wencheng   Ma Hongliang   Jin Zuanming   Dai Ye  

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Spatio-temporal coupling characteristics of ultrafast laser pulse are quantitatively tailored. An asymmetric microstructure is induced in the focal volume when laser scans perpendicular to the direction of spatial chirp in fused silica. The tilted direction reverses when adding a Dove prism into the light path. The sign of pulse front tilt can be turned from positive to negative by changing the group delay dispersion by step. We reveal that tilted direction of microstructure depends on spatial chirp and the interplay between spatio-temporal chirp leads to the change of tilted angles.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Liu Shun   Lu Ping   Chen Enci   Ni Wenjun   Liu Deming   Zhang Jiangshan   Lian Zhenggang  

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This letter shows Vernier effect based on two segments of PANDA polarization maintaining fiber (PMF) whose length is 28 cm and 23 cm, respectively. The two PMF is spliced together and the angle between the fast axes is set to 45°. This cascaded PMF is inserted in a Sagnac loop to form an interferometer which can generate Vernier effect. The spectrum consists of finesse fringe and envelope and realize simultaneous measurement of strain and temperature. The envelope can provide strain and temperature sensitivities of 58.0 pm/με and -1.05 nm/°C. The finesse fringe provides sensitivities of 5.9 pm/με and -1.36 nm/°C.

       PDF全文        Chinese Optics Letters ，2019年第17卷第8期 pp.08      

Guo Hui   He Ruyong   Wei Chaopeng   Lin Zequn   Wang Le   zhao shengmei  

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In this paper, we propose an advanced framework of ghost edge imaging, named compressed ghost edge imaging (CGEI). In the scheme, a set of structured speckle patterns with pixel shifting are illuminated on an unknown object. The output is collected by a bucket detector without any spatial resolution. By using compressed sensing algorithm, we obtain horizontal and vertical edge information of the unknown object with the bucket detector detection results and the known structured speckle patterns. The edge is finally constructed via two-dimensional edge information. The experimental and numerical simulations results show that the proposed scheme has a higher quality and reduces the number of measurements, in comparison with the existed edge detection schemes based on ghost imaging.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Zhang Yinlong   Liang YiZhi   Jin Long   Guan Bai-Ou  

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All-optical ultrasound probe, which contains a photoacoustically based ultrasound generator paired with a photonic acoustic sensor, provide promising imaging modality for diagnostic and MRI compatible applications. Here, we demonstrate the fabrication of a fiber-based all-optical ultrasound probe and its application in pulse-echo ultrasound imaging. The ultrasound generator is fabricated on a 125-μm multimode optical fiber by forming a light-absorbing multiwalled carbon nanotubes (MWCNTs)-polydimethylsiloxane (PDMS) composite coating on its distal end. A peak-to-peak acoustic pressure 0.95 MPa has been achieved at nearly the damage threshold 2.46 μJ, by chemically functionalizing the fiber surface to enable strong nanotube adsorption. Ultrasound reception was performed by a fiber-laser ultrasound sensor which translates ultrasound pressure into differential lasing-frequency changes. By linearly scanning the probe, ex vivo two- and three-dimensional imaging of a segment of swine trachea has been demonstrated, by detecting the echo ultrasound signals and reconstructing the acoustic scatters. The probe presents axial and lateral resolutions at 150 and 62 μm, respectively. The small-sized, side-looking all-fiber ultrasound probe presents a promising approach for assembling an interventional endoscopy.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Huang Junchao   Wang Lingke   Duan Yifei   Huang Yafeng   ye meifeng   Liu Liang   Li Tang  

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We demonstrate frequency stabilization of a 1.55 μm erbium-doped fiber laser by locking it to a 5-km-long optical fiber delay line (FDL). The stabilized laser is characterized via comparison with a second identical laser system. We obtain fractional frequency stability of better than 3*10-15 over timescales of 1–10 s and a laser linewidth of 0.2 Hz, which is the narrowest linewidth of an FDL-stabilized laser observed to date.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

huang wei   cui yulong   Li zhixian   zhou zhiyue   Wang Zefeng  

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We reported here a single-pass 1.56 μm fiber gas Raman laser in a deuterium-filled hollow-core fiber and a 2.86 μm cascade fiber gas Raman laser with methane in the second stage. The maximum output power of 1.56 μm and 2.86 μm is 27 mW and 8.5 mW with Raman conversion efficiency of 30% and 42% respectively. The results offer a new method to produce 1.5 μm fiber source and prove the potential of the cascade fiber gas Raman laser in extending the available wavelength.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Zhang Min   Xu Bo   Li Xiaoyun   Cai Yi   Wu Baojian   Qiu Kun  

      摘要 + 此论文可免费阅读 (可能需要登录)

A novel predictive dynamic bandwidth allocation (DBA) method based on Long Short-Term Memory (LSTM) neural network is proposed for 10-Gigabit-capable passive optical network in mobile front-haul (MFH) links. By predicting the number of packets that arrive at the optical network unit buffer based on LSTM, the round-trip time delay in traditional DBAs can be eliminated to meet the strict latency requirement for MFH links. Our study shows that LSTM has better performance than feed-forward neural network. Based on extensive simulations, the proposed scheme is found to be able to achieve the latency requirement for MFH and outperforms the traditional DBAs in terms of delay, jitter and packet loss ratio.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Lu Chenghao   Zhu Bing   Zhu Chuanyi   Ge Licheng   Liu Yi'an   Chen Yuping   Chen Xianfeng  

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All-optical logic gates including AND, XOR, and NOT gates, as well as a half-adder, are realized based on two-dimensional lithium niobate photonic crystal (PhC) circuits with PhC micro-cavities. The proposed all-optical devices have an extinction ratio as high as 23 dB due to the effective all-optical switch function induced by two-missing-hole micro-cavities. These proposed devices can have potential implementation of complex integrated optical functionalities including all-optical computing in lithium niobate slab or thin film.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Wang Aimin   Yang Wan   Wu Danlei   Wu Runlong   Liu Guanyu   Chen Bingying   Feng Lishuang   Zhang Zhigang  

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We present a Er:fiber based femtosecond laser at 780 nm with 256-MHz repetition rate, 191-fs pulse duration, and over 1-W average power. Apart from the careful third-order dispersion management, we introduce moderate self-phase modulation to broaden the output spectrum of the Er:fiber amplifier and achieve 193-fs pulse duration and 2.43-W average power. Over 40% frequency doubling efficiency was obtained by a periodically poled lithium niobate crystal. Delivering through a hollow-core photonics bandgap fiber, this robust laser becomes an ideal and convenient light source for two-photon autofluorescence imaging.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Zhang Pan   Liu Dean   Yang Aihua   Zhu Jianqiang  

      摘要 + 此论文可免费阅读 (可能需要登录)

A method is proposed to optimize the recording structure of the photorefractive volume grating to compensate the high spatial frequency in the distorted wavefront by optical phase conjugation. Based on coupled-wave equation, the diffraction efficiency of the recorded grating formed by the scattered beams in different recording structures is simulated. The theoretical results show that the recorded modulations with high spatial frequency can be significantly improved in the small recording angle. In experiment, three recording structures with the recording angle 7.5°, 30° and 45° are chosen to verify the compensation effect. Compared with the reconstructed image in the large recording angle 45°, the signal to noise ratio of image recorded in 7.5° increases to 3.2 times.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Sun Xiaocong   Wang Yajun   Tian Long   Zheng Yaohui   Peng Kunchi  

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Squeezed states belong to the most prominent nonclassical resources. They have compelling applications in precise measurement, quantum computation and detection. Here, we report on the direct measurement of 13.8 dB squeezed vacuum states by improving the interference eciency and gain of balanced homodyne detection. By employing an auxiliary laser beam, the homodyne visibility is increased to 99.8%. The equivalent loss of the electronic noise is reduced to 0.05% by integrating a junction eld-eect transistor (JFET) buering input and another JFET bootstrap structure in the balanced homodyne detector.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Miao Runlin   Tong Mingyu   Yin Ke   Ouyang Hao   Wang Zhenyu   Zheng Xin   Cheng Xiangai   Jiang Tian  

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In this work, a soliton mode-locked erbium-doped fiber laser (EDFL) with a high-quality molecular beam epitaxy (MBE) grown topological insulator (TI) Bi2Se3 saturable absorber (SA) is reported. To fabricate the SA device, a 16-layer Bi2Se3 film was grown successfully on a 100 μm thick SiO2 substrate and sandwiched directly between two fiber ferrules. The TI-SA had a saturable absorption of 1.12 % and a saturable influence of 160 MW/cm2. After inserting the TI-SA into the unidirectional ring-cavity EDFL, self-starting mode-locked soliton pulse trains were obtained at a fundamental repetition rate of 19.352 MHz. The output central wavelength/pulse energy/pulse duration/signal to noise ratio (SNR) of radio frequency spectrum were 1530 nm/18.5 pJ/1.08 ps/60 dBm, respectively. These results demonstrate that MBE technique could provide a controllable and repeatable method for the fabrication of identical high-quality TI-SAs, which is critical important for ultrafast pulse generation.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Wang Yan   Lin Nan   Gao Wanli   Song Huanyu   Hu Minglie   Li Haiming   Bao Wenxai   Ma Xiaoyu   Zhang Zhigang  

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We demonstrate a strain compensated long lifetime SESAM with a high modulation depth for fiber lasers. The SESAM was measured to have a damage threshold of 9.5 mJ/cm², a modulation depth of 11.5%, a saturation fluence of 39.3 µJ/cm², and an inversed saturable absorption coefficient of 630 mJ/cm². The SESAM has been applied to a linear cavity mode-locked Yb:fiber laser, which has been working for more than a year without damage of the SESAM.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Sun ShengZhi   Ye Song   Wang Zhenyan   Song Juan   Qian Bin   Qiu Jianrong  

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We report on the elemental redistribution behavior in oxyfluoride glasses with a high repetition rate near-infrared femtosecond laser. Elemental analysis by Electro-Probe Microanalyzer demonstrates that the redistributions of Ca2+ and Yb3+ ions change dramatically with pulse energy, which are quite different compared with previous reported results. Confocal fluorescence spectra of Yb3+ ions demonstrate that the luminescence intensity changes obviously with the elemental redistribution. The mechanism of the observed phenomenon is discussed. This observation may have potential applications in the fabrication of micro-optical devices.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Xu Aopeng   Kong Delong   Fu Zhijie   Wang Zhaoying   Lin Qiang  

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For most of atom interferometers, vibration isolation unit is applied to reduce vibration noise. In our experiment, instead of isolation, the vibration signals are monitored, combining with the sensitive function, the compensation phase shift for the atom interferometer is obtained. We focused on the correction over a wide spectrum rather than on “monochromatic” frequencies. The sensitivity of the atom gravimeter can be upgraded by a factor of more than two. Furthermore, we demonstrated that the atom interferometer can still produce a good measurement result without passive vibration isolation in extremely noisy environments by using vibration compensation.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Li Jian   Xu Yang   Zhang Mingjiang   Zhang Jianzhong   Qiao Lijun   Wang Tao  

      摘要 + 此论文可免费阅读 (可能需要登录)

We propose and experimentally demonstrate a novel Raman-based distributed fiber-optics temperature sensor for improving the temperature measurement accuracy and engineering applicability. The proposed method is based on the double-ended demodulation with a reference temperature and dynamic dispersion difference compensation method, which can suppress the effect of local external physics perturbation and intermodal dispersion on temperature demodulation results. Moreover, the system can omit the pre-calibration process by using the reference temperature before the temperature measurement. The experimental results of dispersion compensation indicate that the temperature accuracy optimizes from 5.6 ℃ to 1.2 ℃, and the temperature uncertainty decreases from 16.8 ℃ to 2.4 ℃. Moreover, the double-end configuration can automatically compensate the local external physics perturbation of the sensing fiber, which exhibits a distinctive improvement.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Zhang Yuxia   Yang Yilun   Zhang Lianhan   Lu Dazhi   Xu Min   Hang Yin   Yan Shishen   Yu Haohai   Zhang Huaijin  

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Praseodymium ion doped gain materials have the superiority of lasing at various visible wavelengths directly. Simple and compact visible lasers are booming with the development of blue laser diodes in recent years. In this paper, we demonstrate the watt level red laser with a single blue laser diode and Pr:YLF crystal. On this basis, the passively Q-switched pulse lasers are obtained with monolayer graphene and Co:ZnO thin film as the Q-switchers in the visible range.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Wang Meng   Wang fan   Feng Suya   Yu Chunlei   Wang Shikai   Zhou Qinling   Zhang Lei   Lou Fengguang   Chen Danping   Hu Lili  

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A large-mode-area (LMA) ytterbium doped photonic crystal fiber (PCF) with core NA of 0.034 and core diameter of 50 μm was made by stack-and-draw technique. The core is formed by Yb3+/Al3+/F-/P5+ co-doped silica glass containing 0.09 mol% Yb2O3 with absorption coefficient at 976 nm up to 3.2 dB/m. The core glass with homogeneous distribution of Yb3+ ions and refractive index difference of 4×10-4 compared with pure silica was prepared by sol-gel method and heat homogenization at 2000°C. Laser power amplification of this LMA PCF was studied using a seed source of 21 picosecond pulse duration and 48.7MHz repetition rate at 1030 nm wavelength. With pump power of 520 W, a maximum 272 W (266 KW peak power) quasi single-mode laser output with M2 of 2.2 was achieved in a 4.7 m fiber length bent at a diameter of 47 cm with slope efficiency of 52%, and no obvious mode instability, SRS or thermal damage on end facet of fiber were observed.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Ruan Cunjun   Kong Deyin   Dai Jun   Chen Kanglong   Guo Sujie   Wu Xiaojun  

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The high-resolution frequency domain spectroscopy (FDS) is set up using coherent and continuous wave terahertz emitter and receiver. Terahertz waves are generated and detected by two photomixers with two distributed feedback (DFB) lasers. Atmospheric water vapor with different relative humidity is systematically investigated by the FDS. A high frequency resolution of ~14 MHz is obtained with the help of Hilbert transformation, leading a well resolved and distinct transmittance characterization of water vapor. Compared with conventional THz time domain spectroscopy (TDS), the high-resolution continuous wave THz spectrometer is one of the most practical system in gas-phase molecular sensing, identification, and monitoring.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Li Zhigang   Yang Rui   Sun Meiyu   Han Jing   Zhang Dengying   chen jiannong   Zhang Dawei   Zhu Linwei  

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In this letter, we propose a simple and effective approach for transforming conventional Talbot array illuminator (TAI) with multilevel phase steps into a binary-phase Talbot array illuminator (BP-TAI) through the detour phase encoding. The BP-TAI is a binary (0 π) phase-only diffractive optical element, which can be utilized to generate a large-scale focal spots array with a high compression ratio. As an example, we design a square BP-TAI with the fraction parameter β=15 for achieving a square multifocal lattice with a high compression ratio β^2. Theoretical analysis and experimental results demonstrate that the detour phase encoding is efficient for designing the BP-TAI, especially with the high compression ratio. Such results may be exploited in practical large-scale optical trapping and X-ray imaging.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Ruan Zuliang   Pei Li   Zheng Jingjing   Wang JianShuai   Wu Liangying   Ning Tigang   Wang Ji  

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A refractive index intensity detecting sensor with long-period grating written in the single mode - thin core - single mode fiber structure is proposed and optimized theoretically. The sensor is composed of two single-mode fibers connected by a section of long period fiber grating fabricated on thin-core fiber. After optimization and benefit from phase matching point, the loss peak of the structure can reach to 62.8dB theoretically. The wavelength of the characteristic peak is fixed at the phase matching point, so the intensity detection can be achieved. The sensitivity can reach to 272.5dB/RIU. The structural optimization of this paper provides a reference for the fabrication of an easy-made all-fiber sensor without extra cladding.

       PDF全文        Chinese Optics Letters ，2019年第17卷第7期 pp.07      

Li Min   Liu Xin   Zhang Ang   Xian Hao  

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The precise alignment of high-performance telescope is a key factor to ensure the imaging quality. However, for telescopes with wide field of view, the images are sometimes under-sampled. To study the effects of under-sampled images on the precision of telescope alignment, numerical simulations are implemented with stochastic parallel gradient descent (SPGD) algorithm. The results show that the alignment program can converge stably and quickly. However, with the reduction of full width at half maximum (FWHM) of images, the relative residual errors increase from 9.5% to 19.5%, and the wavefront errors raise from 0.0972λ to 0.1074λ, indicating the accuracy of alignment decreases.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Zheng Yu   Sun Fang-Wen  

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Forward-scattering-light interferometry has become the most commonly used position detection scheme in optical levi-tation system. Usually, 3-set detectors are required to obtain the 3-dimensional motion information. Here, we simplify the 3-set detectors to one set by inserting a Dove prism. With an optical levitation system in vacuum, we investigate the role of Dove prism in the position measurement process. The relationship between power spectral density and ro-tation angle of Dove prism is experimentally demonstrated and analyzed. This work shows that the Dove prism can much reduce the complexity of experimental setup, which can be applied in the compact optical levitation system for studies in metrology, quantum physics and biology.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Hou Zhi-Shan   Cao Jia-Ji   Li Aiwu   Yang Han  

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Based on natural protein materials, a series of lenses with different height and focal length were assembled on glass substrates by femtosecond laser non-contact, masking and cold processing. This lens array itself possesses unique and characteristic optical performance in three-dimensional parallel imaging and bending imaging. What is more profound is that by using equilibrium swelling of protein-hydrogel, once the lens array was placed in liquid environment, with the change of ion concentration (eg. pH), the refractive index and curvature of the protein-hydrogel would change, which leads to the flex of focal plane of the lens, finally realizes the dynamically tunable of protein microlens. These smart stress device may have great potential in optical biosensing and microfluidic chip integrated field.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Wu Chenchen   Liu Ning   Hu Hai   Guo Xiangdong   Liao Baoxin   Liu Jiaming   Wang Liming   Chen Chunying   Yang Xiaoxia   Dai Qing  

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Abstract: Monitoring the chemical and structural changes in protein side chains and endpoints by infrared spectroscopy is important to study the chemical reaction and physical adsorption process of proteins. However, the detection of side chains and endpoints in nanoscale proteins is still challenging due to its weak infrared response. Here, by designing a double-layered graphene plasmon sensor on MgF2/Si substrate in the IR fingerprint region, we detect the vibrational modes in side chains and endpoints (1397 cm-1 and 1458 cm-1) of monolayer protein. The sensor could be applied on biochemistry to investigate the physical and chemical reaction of biomolecules.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Pan Yijie   Liao Wenhan   Wang He   Yao Yan   Cai Jinhui   Qu Jifeng  

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Atomic Doppler broadening thermometry(DBT) potentially is an accurate and practical approach for the thermodynamic temperature measurement. However, previous reported atomic DBT had a long acquisition time and had only been proved at the triple point of water, 0℃, for the purpose of determination of the Boltzmann constant. This research implemented the Cesium atomic DBT for fast room temperature measurement. Cs133 D1(6S1/2→6p1/2 transition) line was measured by direct laser absorption spectroscopy, and quantity of thermal-induced linewidth broadening was precisely retrieved by the Voigt profile fitting algorithm. The preliminary results showed the proposed approach had a 4 minutes single-scan acquisition time and a 0.2% reproducibility. It is expected that the atomic DBT could be used as an accurate, chip-scale, and calibration-free temperature sensor and standard.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Sun Yuxiang   Wang Mengxia   Wang Xinle   Zhou Ying   Wang Bo   Wang Zhengping   Yu Fapeng   Xu Xinguang  

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With tin diselenide (SnSe2) film as saturable absorber (SA), the passively Q-switched self-frequency doubling (SFD) lasers were realized in Nd3+:ReCa4O(BO3)3 (Re = Y, Gd) crystals. For Nd:YCOB crystal, the maximum average output power at 532 nm was 19.6 mW, and the corresponding pulse repetition frequency, pulse duration, single pulse energy and peak power were 17.6 kHz, 91.9 ns, 1.1 µJ, 12.1 W, respectively. For Nd:GdCOB crystal, these values were 14.5 mW, 22.1 kHz, 48.7 ns, 0.66 µJ and 13.5 W.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Hu Hai   Zhao Jianyang   Wang Weimin   Ho James   Kuang Langxing   Liu Wenbin  

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High power LASER diodes (LD) with a lasing wavelength between 700-780 nm have great potential in various medical use. Here we report our recent efforts in developing InGaAsP/AlGaInP based commercial high power edge-emitting LD which has 755 nm emission peak with a world-record continuous wave (CW) output power of 12.7 W, the highest reported so far. The lack of Al atoms in active region significantly lowers the chance of catastrophic optical damage (COD) during high power laser operation. Meanwhile, with accumulated 3800 running hours, our ongoing aging tests reveal excellent reliability of our devices.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Hu Kai   Yi Lilin   Wei Wei   Hu Weisheng  

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We propose a general guideline on the design of stimulated Brillouin scattering (SBS) based microwave photonic filter (MPF) using directly-modulated pump. Filter gain profiles and passband ripples with the waveform repetition periods of the driving current ranging from 2 ns to 100 ns are measured after transmission of different fiber length. The results show that the filter performance has nothing to do with the fiber length and the DAC bandwidth requirement for the driving current is no more than 500MHz. Therefore the low cost, flexible reconfiguration and miniaturization characteristics make SBS filter using directed-modulated pump a promising choice as MPF.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Lu Hao   Wu Ying   xie wenjing   tang qi   Han Caiqin   Liu Ying  

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The changes of mechanical properties and biological activities of monomeric erythrocytes are studied using the optical tweezers micromanipulation technology. Firstly, the mechanical properties of irradiated erythrocyte membranes are obtained. Weaker power laser irradiation can delay the decay of the mechanical properties of erythrocytes, and promote the biological activity of erythrocytes, while higher power laser irradiation damages erythrocytes. The stronger the laser irradiation is, the more obvious and rapid the damage will be. The temperature of the cell surface will be changed by regulating the laser power and irradiation time, so the biological functions of erythrocyte can be controlled. Secondly, the finite element simulation of the temperature change on the cell surface under the condition of laser irradiation is carried out using a simulation software, and the precise temperature of the cell surface irradiated cumulatively by a laser with different powers is obtained. Finally, the processes of abscission, unfolding and denaturation of hemoglobins in erythrocytes at different temperatures due to the photothermal effect are analyzed using the model. The mechanism of the laser irradiation on the elasticity of erythrocyte membranes is also obtained.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Zhang Haifeng   Long Mingliang   Deng Huarong   Wu Zhibo   Chen zhi'en   Zhang Zhongping  

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Space debris laser ranging was achieved with a 60-W, 200-Hz, 532-nm nanosecond slab, single-frequency green laser at the Shanghai Astronomical Observatory's 60-cm satellite laser ranging system. There were 174 passes of space debris measured in 2017, with the minimum radar cross section (RCS) being 0.25 m², and the highest ranging precision up to 13.6 cm. The RCSs of space debris measured with the farthest distances in 174 passes was analyzed. The results show that the farthest measurement distance (R) and RCS (A) was fitting to R=1388.159A^0.24312, indicating that this laser can measure the distance of 1388.159 km at a RCS of 1 m², which is very helpful to surveillance and research on low-Earth-orbit space debris.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Lu Tingting   Ma Jian   Zhu Xiaolei   Chen Weibiao  

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An external frequency doubling electro-optically Q-switched Nd:YAG 473 nm blue laser was demonstrated. With absorbed pump energy of 48 mJ at 100 Hz repetition rate, about 2 mJ of 473nm blue laser pulse energy was achieved by cascade frequency doubling. The second harmonic conversion efficiency was 64.5% and overall optical-optical efficiency was 4.2%, respectively. The blue laser pulse width was less than 10ns and beam quality factor was less than 2.4.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Song Wei   Zheng Shanguang   Fu Yanan   Min Changjun   Zhang Yuquan   Xie Zhenwei   Yuan Xiao-Cong (Larry)  

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Controlling both amplitude and phase of light in subwavelength scale is a challenge for traditional optical devices. Here we propose and numerically investigate a novel plasmonic meta-hologram, demonstrating broadband manipulation of both phase and amplitude in subwavelength scale. In the meta-hologram, phase modulation is achieved by the detour phase distribution of unit cells, and amplitude is continuously modulated by a T-shaped nano-cavity with tunable plasmonic resonance. Compared to phase-only hologram, such meta-hologram could reconstruct 3D images with higher signal-to-noise ratio and better image quality, and thus offering great potential in applications such as 3D displays, optical communications, and beam shaping.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Luo Peng   Hao Qiang   Fu Hanmei   Zeng Heping  

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We demonstrate here an environmentally stable and extremely compactable Er-doped fiber laser system capable of delivering sub-100-fs temporal duration at repetition rate at 10 MHz. This laser source employs a SESAM mode-locked soliton laser to generate seed pulses. A single-mode-fiber (SMF) amplifier and a double-cladding fiber (DCF) amplifier (both with double-pass configuration) are bridged by a divider and used to manage the dispersion map and boost the soliton pulses. With the help of ×64 replicas, as high as 60-nJ energy within 95-fs duration are obtained at 10 MHz, corresponding to 600-kW peak power.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Yuan 元晴晨 Qingchen   Liang 方亮 Fang   Zhao 赵强 Qiang   Wang 王亚东 Yadong   Mao 毛博 Bo   Khayrudinov Vladislav   Lipsanen Harri   Sun 孙志培 Zhipei   Zhao Jianlin   Gan Xuetao  

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The position-dependent mode couplings between a semiconductor nanowire (NW) and a planar photonic crystal (PPC) nanocavity are studied. By scanning a NW across a PPC nanocavity along the hexagonal lattice's Γ-M and M-K directions, the variations of resonant wavelengths, quality factors, and mode volumes in both fundamental and second-order resonant modes are calculated, implying optimal configurations for strong mode-NW couplings and light-NW interactions. For the fundamental (second-order) resonant mode, scanning a NW along the M-K ( Γ-M ) direction is preferred, which supports stronger light-NW interactions with larger NW-position tolerances and higher quality factors simultaneously. The simulation results are confirmed experimentally with good agreements.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Han Yuxiao   Gu Bing   Zhang Shuai   Rui Guanghao   He Jun   Cui Yiping  

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Understanding the nonlinear optical effect of novel materials plays a crucial role in the fields of photonics and optoelectronics. Herein, we theoretically and experimentally investigate the simultaneous presence of third-order locally refractive nonlinearity and thermally induced nonlocal nonlinearity saturation. We present analytical expressions for the closed-aperture Z-scan trace and the number of spatial self-phase modulation (SSPM) rings, which allows one to unambiguously and conveniently separate the contributions of local and nonlocal nonlinear refraction in the case that both effects occur simultaneously. As a test, we study both the local and thermally induced nonlocal nonlinear refraction in fullerene/toluene solution by performing continuous-wave Z-scan and SSPM measurements at two different wavelengths. This work enriches the understanding of physical mechanism of optical nonlinear refraction effect in solution dispersions of nanomaterials which can be exploited for nonlinear photonic devices.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Mandal Gour   Mukherjee Rahul   Mallick Khaleda   Mandal Paulomi   Patra Ardhendu  

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We have projected and verified a bidirectional intra-/inter-radio-access-technology carrier-aggregation method for next-generation heterogeneous mobile network supported Filter-bank multi-carrier. Successful transmission of intra/inter-band carrier-aggregation between five broadband FBMC signal and three bands 4G-LTE-A signal over 50-km SMF plus 10-m free-space are successfully broadcasted by employing incoherent light-injection scheme in downlink. In uplink, two intra-bands carrier-aggregated WLAN IEEE 802.11g signal is carried over the equal distance. High receiver sensitivity, low EVM, clear constellation diagrams show successful delivery of different wireless services for different consumers. Therefore, proposed hybrid-system should become potential solution for future mobile-fronthaul network because of its low latency and high-capacity.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Qian Guang   Niu Bin   Wu Zhao   Kan Qiang   Gu Xiaowen   Zhou Fengjie   Kong Yuechan  

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In this paper, we reported the preliminary results of an integrating periodically capacitive-loaded travelling wave electrode (CL-TWE) Mach-Zehnder modulator (MZM) based on InP-based multiple quantum well (MQW) optical waveguides. The device configuration mainly includes an optical Mach-Zehnder interferometer (MZI), a direct current (DC) electrode, two phase electrodes and a CL-TWE consisting of a U-electrode and an I-electrode. The modulator was fabricated on 3-inches InP epitaxial wafer by standard photolithography, ICP dry etching, wet etching, electroplating and etc. Measurement results show that the MZM exhibits a 3 dB electro-optic bandwidth of about 31 GHz, a Vπ of 3 V, and an extinction ratio of about 20 dB.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

li long   pan yan   Cui yang   liu rong   yang cheng   liu lan   tian yingzhong   wang bin  

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The Depth of Focus (DFF) is a technique for estimating the depth and 3D shape of an object from a multi-focus image sequence. At present, focus evaluation algorithms based on DFF technology will always cause inaccuracies in deep map recovery from image focus. There are two main reasons behind this issue. The first is that the window size of the focus evaluation operator has been fixed. Therefore, for some pixels, enough neighbor information cannot be covered in a fixed window and is easily disturbed by noise, which results in distortion of the model. For other pixels, the fixed window is too large, which increases the computational burden. The second is the level of difficulty to get the full focus pixels even though the focus evaluation calculation on the actual calculation process has been completed. In order to overcome these problems, an adaptive window iteration algorithm is proposed to enhance image focus for accurate depth estimation. This algorithm will automatically adjust the window size based on gray differences in a window that aims to solve the fixed window problem. Besides that, it will also iterate evaluation values to enhance the focus evaluation of each pixel. Comparative analysis of the evaluation indicators and model quality has shown the effectiveness of the proposed adaptive window iteration algorithm.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Huang Yong   Wu Chuanchao   Xia Shaoyan   Liu Lu   Chen Shanlin   Tong Dedi   Ai Danni   Yang Jian   Wang Yongtian  

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Vascular Doppler optical coherence tomography (DOCT) images with weak boundaries are usually difficult for most algorithms to segment. We propose a modified random walk algorithm (MRW) with a novel regularization for the segmentation of DOCT vessel images. Based on MRW, we perform automatic boundary detection of vascular wall from intensity images and boundary extraction of blood flowing region from Doppler phase images. Dice coefficient, sensitivity coefficient and specificity coefficient were adopted to verify the segmentation performance. Experimental study on DOCT images of the mouse femoral artery, showed the effectiveness of our proposed method, yielding 3D visualization and quantitative evaluation of the vessel.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Xia Huijuan   Yang Shumin   Wang Liansheng   Zhao Jun   Xue Chaofan   Wu Yanqing   Tai Renzhong  

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Achromatic Talbot lithography (ATL) with high resolution has been demonstrated to be an excellent technique for large area periodic nano-fabrication. In this work, the uniformity of pattern distribution in ATL was studied in detail. Two ATL transmission masks with ~50% duty cycle in square lattice were illuminated by a spatial coherent broadband EUV beam with a relative bandwidth of 2.38%. Nonuniform dot size distribution were observed by experiments and FDTD simulations. The sum of the two kind of diffraction patterns, with different lattice direction (45° rotated) and different intensity distribution, results in the final nonuniform pattern distribution.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Song Weitao   Cheng Qijia   Liu Yue   Zheng Yuanjin   lin zhiping   Wang Yongtian  

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We proposed a three-dimensional (3D) image authentication method using binarized phase images in a double random phase integral imaging (InI). Two-dimensional (2D) element images obtained from integral imaging are encoded using a double random phase encryption (DRPE) algorithm. Only part of the phase information is used in the proposed method rather than using all of the amplitude and phase information, which can make the final data spare and beneficial to data compression, storage, and transmission. Experimental results verified the method, and successfully proved the developed 3D authentication process using a nonlinear cross correlation method.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Wang Xiangchuan   Li Shupeng   Jiang Xin   Hu Jintao   Xue Min   Xu Shangzhe   Pan Shilong  

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Optoelectronic components and subsystems such as optically controlled phased array antennas, distributed radar networks, interferometric optical fiber hydrophones and high-speed optoelectronic chips demand for high accuracy optical time delay measurement with large measurement range and capability for single-end and wavelength-dependent measurement. In this paper, the recent advances in the optical time delay measurement of fiber link with high accuracy are reviewed. The general models of the typical time delay measurement technologies are established with the operational principle analyzed. The performance of these techniques is also discussed.

       PDF全文        Chinese Optics Letters ，2019年第17卷第6期 pp.06      

Zhao Zhigang   Kuroda Kenta   Harasawa Ayumi   Kondo Takeshi   Shin Shik   Kobayashi Yohei  

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A monolithic Lens-Window-Prism (LWP) device, made of lithium fluoride (LiF) or magnesium fluoride (MgF2), was proposed. When either of the devices was fixed onto one end of a gas cell filled with Xe, it becomes a “wedge-crystal” like device and was used to convert a 1-MHz femtosecond 347 nm laser to its third harmonic radiation at 10.7 eV. This led to an improved beam profile, a more compact and less lossy configuration. A stable output power of ~11 μW was demonstrated for 2 hours using LiF-LWP. In addition, MgF2-LWP was also verified for its practicability at 10.7 eV.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

chang yawei   jiang tongxiao   Zhang Zhigang   Wang Aimin  

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We demonstrate an all-fiber Yb:fiber frequency comb with nonlinear-amplifying-loop-mirror based Yb:fiber laser oscillator. The fiber-spliced hollow-core photonic bandgap fiber was used as dispersion compensator, which was also directly spliced to a piece of tapered photonic crystal fiber for octave-spanning spectrum. The spectrum of the compressed 107 fs laser pulses was broadened, covering 600 nm to 1300 nm in a high-nonlinearity tapered fiber for f to 2f beating. The signal-to-noise ratio of offset frequency was measured to be 22 dB.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Tsang Peter   Poon T.-C.   Wang William   Zhu Xiuling   Chan Kenny  

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Past research has demonstrated that a sampled phase-only hologram (SPOH) is capable of representing an image without the magnitude component of the hologram. At present, a SPOH can only record and reconstruct a single source image. In this paper we propose, for the first time, a method for representing multiple images with a single integrated SPOH (ISPOH). Subsequently, each image can be retrieved from the ISPOH with a unique key parameter, and displayed as a visible image on a phase-only spatial light modulator.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Wang Haoyu   Zheng Jun   Fu Yifei   Wang Chengliang   Huang Xinran   Ye Zhicheng   Qian Liejia  

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Separating lights into different paths according to the polarization states while keeping respective path's polarizations with high purification is keen for polarization multiplex (PMX) in optical communications. Metallic nanowire gratings (MNGs) with multi-slits in a period are proposed to achieve polarized beam splitters (PBSs) in reflection and diffraction. The setting of multi-slits largely reduces the reflection of photons with transverse magnetific field (TM) via plasmonic waveguiding effect, which leads to highly polarized output lights with extinction ratio (ETR) larger than 20 dB in each channel. The proposed reflection/diffraction PBSs enrich the approaches to control the polarization states with the advantages of wide incident angles and flexible beam splitting angles.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Cheng Ju   Zhang Jia   陆 建   Bian Xintian   Zhang Hongchao   Shen Zhonghua   Ni Xiaowu   Ma Pengcheng   Shi Jin  

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The apatite compound Ca4La6(SiO4)4(PO4)2O2 (CLSPO) was explored as the host material for phosphors used in white light-emitting diodes (wLEDs). The crystal structure of the CLSPO host prepared by the solid-state reaction method was investigated with Rietveld refinement. The Rare-earth ions (Eu3+/ Tb3+/Ce3+, Tb3+/Tb3+, Mn2+) activated CLSPO phosphors were synthesized and their photoluminescence properties, quantum yields as well as thermal stabilities were studied. Under near-ultraviolet excitations, the Eu3+ and Tb3+ doped CLSPO compounds exhibited red and green emissions with high luminescence efficiencies. Besides, tunable emissions from green to orange were obtained by introducing Mn2+ ions into the Tb3+ doped CLSPO samples. The results showed the phosphors studied may have potential applications for wLEDs.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Shisong Wu   Yuanyang Li  

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A 1550-nm all-fiber pulsed laser Doppler vibrometer (LDV) based on time-domain chopping (TDC) techniques is developed to overcome demodulation failures caused by multipath interference. The system adopts an adjustable configuration on pulse duration and pulse repetition frequency according to the distance. An experiment is carried out at a 25 m standoff with a pulse duration of 80 ns, single pulse energy of 0.4 nJ, and pulse repetition frequency of 1 MHz. A waveform and spectrogram of the demodulated voice show that the pulsed LDV system has a good performance in long-range voice listening.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Zhang Quan   Yu Junjie   Shi Biran   Tang Fanchun   Li Jianlang  

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The excitation of high-order Laguerre-Gaussian mode in a Nd:YAG laser resonator was presented by applying the diffraction of a second-order circular Dammann grating (CDG) for annular pumping. In the study, the 808-nm pump light was shaped into double-ring structure by the CDG and matched spatially with that of an ideal LG11 mode. As a result, the laser resonator generated LG11 vortex mode, and the laser power reached 204 mW with 14.5-% slope efficiency. Also, when the cavity mirror was tilted, the laser output could switch to LG01 vortex mode. The results showed the convenience and versatility of CDG in annular-pumped vortex laser.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Sun Licheng   Liu Tinghao   Fu Xing   Guo Yading   Wang Xiaojun   Shao Chongfeng   Zheng Yamin   Sun Chuang   Lin Shibing   Huang Lei  

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In this letter, a 116-actuator deformable mirror (DM) was used to correct the wavefront distortion in a 10.7 J, 10 Hz Nd:YAG slab amplifier. By applying a pump-light homogenizer to transform the 3×1 near-field beam array into an integrated beam, the beam quality was greatly improved from 5.54 times diffraction limited (TDL) to 1.57 TDL after being corrected by the DM. To the best of our knowledge, this is the first investigation on the beam quality control of an arrayed near-field beam in the high-energy diode-pumped solid-state lasers.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Han Xiao-Chuan   Feng Lantian   li yuxuan   Zhang LanXuan   Zhang Yongsheng   Song Junfeng  

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The continuous-time quantum walk (CTQW) is the quantum analogue of the continuous-time classical walk (CTCW), and is widely used in universal quantum computations. Here, taking the advantages of the waveguide arrays, we implement large-scale CTQWs on chips. We couple the single-photon source into the middle port of the waveguide arrays and measure the emergent photon number distributions by utilizing the fiber coupling platform. Subsequently, we simulate the photon number distributions of the waveguide arrays by considering the boundary conditions. The boundary conditions are quite necessary in solving the problems of quantum mazes.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Adzir Mahdi Mohd   Kuen Yao Lau   Pin Jern Ker   Abas Ahmad Fauzi   Alresheedi Mohammed Thamer  

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Saturable absorber is commonly employed to generate ultrashort laser with mode-locking scheme. In an erbium-doped fiber laser system, the laser regimes either 1530 nm or 1550 nm wavelength are procured based on the absorption profile of the erbium-doped fiber. The absorption of erbium-doped fiber is designed to emit at both wavelengths by control the net gain of the laser cavity. Subsequently, simultaneous erbium-doped fiber laser emission is attained at 1533.5 nm and 1555.1 nm with the pulse duration of 910 fs and 850 fs, respectively. Therefore, this work maximizes the output portfolios of mode-locking fiber laser for dual-wavelength ultrashort pulses emission.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

cao zhen   He Hongbo   Hu Guohang   Zhao Yuanan   Yang Liujiang   Shao Jianda  

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A time-resolved high-power laser photometer, which measures the real-time variations of transmission, internal reflection, and scattering simultaneously with picosecond time resolution, was developed to investigate the material response sequence during high-power nanosecond laser irradiation in thick fused silica. It was found that the transient transmission decreased sharply accompanied with an increase in internal reflection at the rising edge of the laser pulse. The transient transmission recovered while laser damage did not occur, but it did not recover if the scattering increased, indicating the occurrence of laser damage. The reason of sharp-decrease of transmission and the relationship between the transmission drop and laser damage were discussed.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

zhang jingang   Nie Yunfeng   Fu Q.   Peng Yifan   Xiang Libin  

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Conventional optical system design employs combinations of different lenses to combat aberrations, which usually leads to considerable volume and weight. In this paper, a tailored design scheme that exploits state-of-the-art digital aberration correction algorithms in addition to traditional optics design is investigated. In particular, the proposed method is applied to the design of refractive telescopes by shifting the burden of correcting chromatic aberrations to software. By enforcing cross-channel information transfer in a post-processing step, the uncorrected chromatic aberrations are well mitigated. Accordingly, a telescope of f-8, 1,400mm focal length, and 0.14° field of view is designed with only two lens elements. The image quality of the designed telescope is evaluated by comparing it to the equivalent designs with multiple lenses in a traditional optical design manner, which validates the effectiveness of our design scheme.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Li Shasha   Shen Baifei   Wang Wenpeng   Bu Zhigang   Zhang Hao   Zhang Hui   Zhai Shuhua  

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Vortex harmonics with fractional average orbital angular momentum are generated when a relativistic fractional vortex beam incidents on and reflects from an overdense plane plasma target. A two-step model is presented to explain the far-field patterns of the harmonics. In the first step, a fundamental spot-shaped hole is produced during the hole-boring (HB) stage, and harmonics are generated simultaneously. In the second step, different order harmonics are diffracted by the hole and propagate to the far-field. This process can be accurately described by Fraunhofer diffraction theory. This work facilitates a basic recognition of fractional vortex beams.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Guo Xi   Xing Zhikun   Qin Huabao   Sun Qizhen   Liu Deming   Zhang Lin   Yan Zhijun  

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We have investigated the whole polarization-extinction-ratio (PER) spectrum and annealing properties of 45°-tilted fiber gratings (45°-TFGs). Experimental results show the PER spectrum of 45°-TFGs is Gaussian-like profile and covers 540nm bandwidth form 1260 to 1800nm, in which the bandwidth with PER greater than 10dB is over 250nm. The output polarization distribution of 45°-TFGs was analyzed by employing a bulk linear polarizer, and the results show a perfect figure “8”, which indicates that the 45°-TFG is a type of linear polarizer. Moreover, the annealing property of 45°-TFGs was measured up to 700 ℃, in which the PER of grating started to decrease at 300℃ and reached to the minimum at 700℃. Based on these results, the 45°-TFGs can be used as ultra-wide bandwidth in-fiber polarizing devices.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

Shi Nuannuan   Li Wei   Zhu Ninghua   Li Ming  

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To overcome the beam squint in wide instantaneous frequency, we review a number of system level optical controlled phase array antenna (OCPAA) for beam forming. The optical delay network based on fiber device in terms of topological structure of N-bit optical switch, fiber grating, high-dispersion fiber, vector-sum technology is discussed, respectively. At last, integrated circuit is simply summarized.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

SHAO DIXIANG   Chen Yao   Zhou T.   Zhang R.   FU ZHANGLONG   Zhuang Songlin   Cao Juncheng  

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Optical frequency combs, which are generated by the cascade of a phase modulator and a Mach-Zehnder intensity modulator, are used as a polychromatic signal source in the terahertz imaging system to improve imaging quality. Interference effect caused by the monochromatic wave has been greatly suppressed. The required optical power in the presented system is as low as ~30% of that in the system using the Er-doped fiber amplifier as source, which can reduce cost and protect photodiodes from damage. This work provides an effective, low power consumption, low cost, and easy way to realize terahertz imaging with high quality, and can be used in the future security inspection.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Yan Dongyu   Liu Bowen   Chu Yuxi   Song Huanyu   Chai Lu   Hu Minglie   Wang Qingyue  

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We report a hybrid femtosecond laser system based on a femtosecond Yb-doped fiber laser and an Yb:KGW regenerative amplifier. To match the central wavelength of the seed source, an Yb:KGW crystal is used in the regenerative amplifier for Np-polarization. We study and optimize the dynamics of nonlinear amplification to alleviate the gain narrowing effect. With optimization, the system can output 270-fs pulses with 21-μJ pulse energy at a 60-kHz repetition rate.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Zhan Yueying   He Jianhua   Wang Fei   Wang Liqian  

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In our paper, we selected several commercial optical transceivers, which consist of single-channel transceiver modules, parallel transmitting and receiving modules, and EPON OLT and ONU modules, to do the total ionizing dose (TID) testing via gamma-ray radiation method. The changing of current and receiver sensitivity of optical transceivers are discussed and analyzed. Based on the TID testing exposed to a total ionizing dose of 50 krad (Si) at a dose rate of about 0.1 rad (Si)/s, the performance of single-channel transceivers and parallel receiving modules have not changed after 50 krad (Si) exposed, the parallel transmitting and EPON ONU modules have not worked after 40 krad (Si) and 47 krad (Si) exposed, the EPON OLT module has bit error in the process of irradiation and it can work well after annealing, and the reason for the error of OLT is analyzed. Finally, based on the theoretical analyzed and testing results, this paper provides several design suggestions to improve the reliability for optical transceivers, which can be referenced by satellite system designation for various space missions.

       PDF全文        Chinese Optics Letters ，2019年第17卷第5期 pp.05      

zhang yanjun   Li Yunchao   Hu Xuwen   Zhang Lu   Liu Zhaojun   Zhang Kaifang   Mou Shihao   Zhang Shougang   Yan Shu-Bin  

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As the key part of chip-scale atomic clocks (CSACs), the vapor cell directly determines the volume stability and power consumption of the CSAC. The reduction of the power consumption and CSAC volumes demands the manufacture of corresponding vapor cells. However, their micro-fabrication is challenging. This overview presents the research development of vapor cells of the past few years and analyzes the shortages of the current preparation technology. By comparing several different vapor cell preparation methods, we successfully realized the micro-fabrication of vapor cells using anodic bonding and deep silicon etching. The microelectromechanical system (MEMS) fabrication process is presented in detail. It is simple and avoids weak bonding strengths caused by alkali metal volatilization during anodic bonding under high temperatures. Finally, the vapor cell D2 line was characterized via optical absorption resonance. According to the results, the proposed method is suitable for CSAC.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Sun Han   wang Lan   Zhang Yaxin   Liang Shixiong   Han Jiaguang   Lan Feng   Zhou Xinlan   Yang Ziqiang  

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This paper presents a double layer structure combined with cracked cross meta-surface and grating surface to realize arbitrary incident linear THz wave polarization conversion. The arbitrary incident linear polarization THz wave will be induced the same resonant modes in the unit-cell, which results in polarization conversion insensitive to the linear polarized angel. Moreover, the zigzag-shaped resonant surface current leads to a strong magnetic resonance between the meta-surface and gratings, which enhanced the conversion efficiency. The experimental results show more than 70% conversion rate can be achieved under arbitrary linear polarized within a wide frequency band. Moreover, around 0.89THz nearly perfect polarization conversion is realized.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Li Hui   Zhao Qingchao   Jiang Shaodong   Ni Jiasheng   Wang Chang  

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A fiber Bragg grating (FBG) and Fabry-Perot (FP) cavity cascaded fiber sensing system was manufactured for temperature and pressure sensing. Temperature high up to 175 ℃ sensing was performed by FBG for the linear variation of FBG wavelength with temperature. After temperature was sensed, the demodulation system can find the original FP cavity length and its pressure-cavity length correlation coefficient, thus the ambient pressure would be calculated. The sensing pressure can be as high as 100 MPa with a repeatability of 1/10000 and high stability. This kind of fiber sensor has been used in Shengli Oil Field.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Gong Dejing   Yuan Yinquan   Liang Lei   Yang Minghong  

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Using theoretical simulations for optical fiber surface plasmon resonance (SPR) sensor and prism based SPR sensor coated with negative permittivity material (NPM), we investigated the effect of the permittivity of NPM on the transmitted spectrum of optical fiber SPR sensor and the reflected spectrum of prism based SPR sensor, and then obtained optimum permittivity of the NPM which can excite the sharpest SPR spectrum in white light region (400-900 nm).

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Shahzadi Mahnoor   Zhang W. L.   Talha Muhammad  

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Exciton-polaritons offer an exceptional platform for future photoelectronic and quantum information applications. The influence of optical Stark effect on exciton-polariton in microcavity embodied with a monolayer WS2 is studied. A polarization dependent model is proposed to study the change of strongly coupled excitons and photons in WS2 microcavity. It is revealed through both steady and dynamical states analysis that an outside optical Stark pulse can effectively vary the polariton characteristics such as dispersion, exciton and photon fractions through blue shifting of excitonic resonance. Thus, the analysis and control of excitons-polaritons in a WS2 microcavity via spin-selective trigger could be achievable.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Ma Yuxuan   Meng Fei   Wang Yan   Wang Aimin   Zhang Zhigang  

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We demonstrate a 0.95 GHz repetition rate fully stabilized Yb:fiber frequency comb without optical amplification. Benefitted from the high mode power and high coherence, this comb achieved 35 dB to 42 dB signal to noise ratio on the direct heterodyne beat signals with at least 6 continuous wave lasers (at 580nm, 679nm, 698nm, 707nm, 813nm and 922 nm) while keeping >40 dB carrier envelop frequency signal. It can be used for the direct measurement of optical frequencies in visible and near-infrared wavelengths, and has a great potential on simultaneous comparison of multiple optical frequencies.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Qian Qizhang   Wang Nan   Zhao Shengzhi   Li Guiqiu   Li Tao   Li Dechun   Yang Kejian   Zang Jie   Ma Houyi  

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Gold nanorods (GNRs) with two different aspect ratios were successfully utilized as saturable absorbers (SAs) in passively Q-switched Nd:LLF laser emitting at 1.34 μm. Based on the GNRs with an aspect ratio of 5, a maximum output power of 1.432 W was achieved, and the narrowest pulse width was 328 ns with a repetition rate of 200 kHz. But in the case of the GNRs with the aspect ratio of 8, a maximum output power of 1.247 W was achieved, and the narrowest pulse width was 271 ns with a repetition rate of 218 kHz. Our experimental results reveal that the aspect ratios of GNRs have different saturable absorption effects at a specific wavelength. In other words, for passively Q-switched lasers at a given wavelength, we are able to select the most suitable GNRs as an SA by changing their aspect ratio.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Li Zhuang   lv xiaoyi  

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Echinococcosis—a parasitic disease caused by Echinococcus granulosus or Echinococcus multilocularis larvae—occurs in many regions in the world. This disease can pose a serious threat to public health and thus requires a convenient and cost-effective method for early detection. So we developed a novel method based on visual saliency and scale-invariant features, that detects the tapeworm parasites .This method improves upon existing bottom-up computational saliency models by introducing a visual attention mechanism. The results indicated that the proposed method offers a higher level of both accuracy and computational efficiency when detecting Echinococcus granulosus protoscoleces, which in turn could improve early detection of echinococcosis.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Xiong Baoxing   Gao Fan   Zhang Xiang   Yuan Xiao  

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The two-dimensional angular filter based on volume Bragg gratings in photothermorefractive glass for ns laser pulse is demonstrated. The experimental results show that the near-field beam quality of laser pulse was effectively improved. The near-field modulation and contrast ratio were improved 1.75 and 4.48 times, respectively. The PSD curves showed that the spatial frequencies more than 0.9mm-1 in x direction and 1.2mm-1 in y direction were effectively suppressed.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

YAN Xu   郭 立新   Chen Minjian   Chai Shuirong  

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Vortex splitting is one of the main causes of instability in orbital angular momentum (OAM) modes transmission. Recent advances in OAM modes free-space propagation have demonstrated that abruptly autofocusing Airy vortex beams (AAVBs) can potentially mitigate the vortex splitting effect. However, different modes of vortex embedding will affect the intensity gradients of the background beams, leading to changes in the propagation characteristics of vortex beams. This study presents the unification of two common methods of coupling autofocusing Airy beams with vortices by introducing a parameter (m) which also controls the intensity gradients and focusing properties of the AAVBs. We demonstrate that vortex splitting can be effectively reduced by selecting an appropriate value of the parameter (m) according to different turbulence conditions. In this manner, the performance of OAM-based free-space optical (FSO) systems can be improved.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Cao Yun   Xiong Jichuan   Liu Xuefeng   Xia Zhiying   Wang Weize   Yadav N.P.   Liu Weiping  

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This paper tackles the issue of non-contact detection of ultrasonic fields by utilizing a novel optical method based on the parametric indirect microscopic imaging (PIMI) technique. A general theoretical model describing the three-dimensional anisotropic photoelastic effect in solid was developed. The mechanism of polarization status variations of light passing through the stress and strain fields was analyzed. Non-contact measurements of ultrasonic field propagating in an isotropic quartz glass have been fulfilled using the PIMI technique under different ultrasonic excitation conditions. PIMI parameters such as sinδ, Φ and the Stokes parameters have been found sensitive to ultrasonic fields.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Liu kai   Wei Qi   Huang Yongqing   Duan Xiaofeng   Wang Qi   Ren Xiaomin   Cai Shiwei  

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An integrated optoelectronic chip pair which can transmit and receive optical signals simultaneously are proposed in this paper. The design and optimization of its key structure, the VCSEL's DBR, is presented. Analysis is also done for its influence on the integrated chip's performance. Moreover, the chip pair's performance under dynamic conditions are analyzed. Their 3 dB modulation bandwidths are higher than 10 GHz and their 3 dB photo-response bandwidths are around 23 GHz. Their applications will further improve the performances of the optical interconnects

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Zhu Lida   Wang Yi   Yuan Yi   Zhou Hongxian   Zhao Yuqian   Ma Zhenhe  

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We demonstrated a method for CCT measurement with a sub-micrometer sensitivity using a spectral domain optical coherence tomography (SD-OCT) system without needing a super broad bandwidth light source. By combining the frequency and phase components of Fourier transform (FT), the method is capable of measurement of a large dynamic range with a high sensitivity. Absolute phases are retrieved by comparing the correlations between the detected and simulated interference fringes. The phase unwrapping ability of the present method was quantitatively tested by measuring the displacement of a piezo linear stage. The human CCTs of six volunteers were measured to verify its clinical application. It provides a potential tool for clinical diagnosis and research applications in ophthalmology.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

chen minghui   jia wenyu   he jintao   geiser martial   zheng gang  

      摘要 + 此论文可免费阅读 (可能需要登录)

This study introduced the research into, and development of, a portable, miniaturised system for the measurement of the refractive index of sub-microlitre liquid based on a microfluidic chip. A technical method, namely, double-beam interference, was proposed for use in the measurement. Based on this, by using a laser diode as a light source, changes in refractive index were calculated by utilising a complementary metal-oxide-semiconductor (CMOS) to detect the movement of interference fringes of the liquid. Firstly, this study simulated the effects of influencing factors on the interference infringes of two Gaussian beams, such as their spot sizes, distance between two beam spots, and detection range. Secondly, this research introduced the system design and construction of the double-beam interference method and analysed the results of refractive index tests on sub-microlitre aqueous glucose solutions with different concentrations therewith. The measurement accuracy reached 10-4 RIU. This system has a compact structure and is rendered portable by using batteries for its power supply. The entire system is designed to be a double Z-shaped structure with a length of about 15 cm, a width of 5 cm, and height of about 10 cm: it can be used to measure changes in refractive index of sub-microlitre to nanolitre liquids based on the use of a microfluidic chip.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Guo Yujian   Alkhazragi Omar   Kang Chun   SHEN CHAO   Mao Yuan   Sun Xiaobin   Ng Tien   Ooi B. S.  

      摘要 + 此论文可免费阅读 (可能需要登录)

This tutorial focuses on devices and technologies that are part of laser-based visible light communication (VLC) systems. Laser-based VLC systems have advantages over their light-emitting-diode-based counterparts, including having high transmission speed and long transmission distance. We summarize terminologies related to laser-based solid-state lighting and VLC, and further review the advances in device design and performance. The high-speed modulation characteristics of laser diodes and superluminescent diodes, the on-chip integration of optoelectronic components in the visible color regime, such as the high-speed integrated photodetector, were introduced. The modulation technology for laser-based white light communication systems, and the challenges for future development were then discussed.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Chen Menglin   Luo Zhijun   Liu Yanan   Gan Zongsong  

      摘要 + 此论文可免费阅读 (可能需要登录)

Fractional density of states (FDOS) hinders the accurate measuring of the overall spontaneous emission (SE) control ability of a three-dimensional (3D) photonic crystal (PC) with the current widely used SE decay lifetime measurement systems. Based on analyzing the FDOS property of a 3D PC from theory and simulation, the excitation focal spot position averaged FDOS with a distribution broadening parameter were proposed to accurately reflect the overall SE control ability of the 3D PC. Experimental work was done to confirm that our proposal is effective which can contribute to comprehensively characterize the SE control performance of photonic devices with quantified parameters.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Yan Wen   Yao Yuan   Sun Yuxin   Hoyt Chad   Jiang Yanyi   Ma Longsheng  

      摘要 + 此论文可免费阅读 (可能需要登录)

We study a Zeeman slower using the magnetic field generated by a coil pair for a magneto-optical trap. The efficiency of the Zeeman slower is shown to be dependent on the intensity and the frequency detuning of the laser light for slowing the atoms. With the help of numerical analysis, optimal experimental parameters are explored. Experimentally, the optimal frequency detuning and intensity of the slowing beam are explored, and 4.2 × 107 ytterbium atoms are trapped in the magneto-optical trap.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Ge Aichen   Liu Bowen   Chen Wei   Tian Haochen   Song Youjian   Chai Lu   Hu Minglie  

      摘要 + 此论文可免费阅读 (可能需要登录)

We demonstrate a coherent synthesis system based on femtosecond Yb-doped fiber laser technology. The output pulse of the amplification system is divided into two replicas, and seeded into photonic crystal fibers of two parallel branches for nonlinear pulse compression. Because of the different nonlinear dynamics in the photonic crystal fibers, the compressed pules show different spectra which can be spliced to form a broad coherent spectrum. The integrated timing jitter between the pulses of two branches is less than one tenth of an optical cycle. By coherently synthesizing pulses from these two branches, 8-fs few-cycle pulses are produced.

       PDF全文        Chinese Optics Letters ，2019年第17卷第4期 pp.04      

Shang Jimin   Zhang Shuai   Wang Yongqiang   Wen Hongyu   Wei Zhongming  

      摘要 + 此论文可免费阅读 (可能需要登录)

The electronic and optical properties of the ZrS2/SnS2 van der Waals heterostructure have been investigated. We find out the formed heterostructure has an intrinsic type-I band alignment. Moreover, the characteristics of optical absorption in heterostructure can be enhanced to the amount of 10^6 in ultraviolet light region. In addition, the tuning electronic properties of ZrS2/SnS2 heterostructure are very interesting, due to the transitions from type-I to type-II band alignment can be occurred by applying an external electric field. These results suggest that the atomically thin materials ZrS2/SnS2 heterostructure will be utilized for the flexible optoelectronic applications.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

wang taijin   wang jiang   Wang Yonggang   yang xiguang   liu sicong   lv ruidong   Chen Zhendong  

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A single output Q-switched Nd: GdVO4 laser with a reflective graphene oxide (GO) saturable absorber was demonstrated. The shortest pulse duration in Q-switched laser is 115 ns and the output power ranges from 1.23 W at 1.71 MHz to 2.11 W at 2.50 MHz when the pump power rises from 7.40 W to 10.90 W, with the utilization of GO Langmuir-Blodgett (LB) films based on the convenient and low-cost LB technique. To the best of our knowledge, It’s the highest output power in Q-switched laser with GO saturable absorber.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Yang Huashan   Zhang Fuling   Leng Lemeng   Zeng Zhaobang   Shao Yue   Zhang Hui   Yang Nan   Chen Xiangning  

      摘要 + 此论文可免费阅读 (可能需要登录)

A simple method improving grating couplers’ coupling efficiency without any extra micro fabrication processes is proposed. This method can improve the coupling efficiency with 1.69dB by utilizing the combined interference in cladding layer and air gap between the cladding surface and the paralleled angle polished fiber facet. The proposed method can be applied to various kinds of on-chip grating couplers. Back reflection, 1-dB bandwidth and fiber alignment tolerance has been also improved at the same time.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Wang Hua   Du Tuanjie   Li Yanhong   Zou Jinhai   Wang Kaijie   Zheng Fuyong   Fu Junfeng   Yang Jihai   Fu Hongyan   Luo Zhengqian  

      摘要 + 此论文可免费阅读 (可能需要登录)

We demonstrated a 2080 nm long-wavelength mode-locked Tm-doped fiber laser operating in the dissipative soliton resonance (DSR) regime. The compact all-fiber dumbbell-shaped laser is simply constructed by a 50/50 fiber loop mirror (FLM), a 10/90 FLM and a piece of large-gain Tm-doped double-clad fiber pumped by a 793 nm laser diode. The 10/90 FLM is not only used as an output mirror, but also acts as a periodical saturable absorber for initiating DSR mode locking. The stable DSR pulses are generated at the center wavelength as long as 2080.4 nm, and the pulse duration can be tunable from 780 ps to 3240 ps as the pump power is increased. The maximum average output power is 1.27 W, corresponding to a pulse energy of 290 nJ and a nearly constant peak power of 93 W. This is, to the best of our knowledge, the longest wavelength for DSR operation in mode-locked fiber laser.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

shan chong   Zhao Yuanan   Gao Yanqi   Zhao Xiaohui   Hu Guohang   Ma Weixin   Shao Jianda  

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The spatial resolved method, which measures the laser-induced damage fluence by identifying the location of damage point at the Gaussian beam three-dimensional direction, is demonstrated. The advantages and practicality of this method has been explained. Taking a triple frequency beam splitter as an example, the defect damage fluence can be calculated by the spatial resolved method accurately. The different defect damage performance of the triple frequency splitter was distinguished under irradiations of 355nm laser only and 532nm laser only. The spatial resolved method provides a way to obtain precise information of optical film defect information.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Zhao Junhao   Xiao Gang   Zhang Xingchen   Bavirisetti Durga Prasad  

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By improving the long-term correlation tracking algorithm (LCT), an effective object tracking method (ILCT) is proposed to address the issue of occlusion. If the object is judged being occluded by the designed criterion, which is based on the characteristic of response value curve, an added re-detector will perform re-detection and the tracker is ordered to stop. Besides, a filtering and adoption strategy of re-detection results is given to choose the most reliable one for the re-initialization of the tracker. Extensive experiments are carried out under the conditions of occlusion and the results demonstrate that ILCT outperforms some state-of-the-art methods in terms of accuracy and robustness.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Zhao Yanting   Song Zixuan  

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We report the observation of ultralow-power absorption saturation in a tapered optical nanofiber（TOF）mounted in a hot cesium vapor in a vacuum chamber. The small optical mode area of TOF produces a great influence on optical properties, allowing optical interactions with nanowatt-level power. The comparison of transmission characteristic for the TOF system and free-space vapor is investigated at different input power and atomic density. The unique performance of the Cs-TOF system makes it promising candidate in resonant nonlinear optical applications with ultralow power.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

liu mengli   Yuyi Ouyang   Hou Huanran   Liu Wenjun   Wei Zhiyi  

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Compared with the extensively studied MoS2 and WS2, tungsten telluride (WTe2) owns smaller bandgap, which is applicable to near-infrared system in photodetectors, communications and ultrafast optic. In this work, the WTe2 SA with the tapered fiber structure is prepared by the magnetron-sputtering technology, which enable the prepared SA to be low in cost and has strong nonlinearity. The modulation depth of prepared WTe2 SA is measured as 31.06%. The Q-switched fiber laser operating at 1.5 μm is successfully investigated by incorporating the proposed SA into the prepared ring cavity. As far as we know, this is the first attempt of WTe2 in the Q-switched fiber laser at 1.5 μm yet.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Jiang Leyong   Tang Jiao   Wang Qingkai   Wu Yuexiang   Zheng Zhiwei   xiang yuanjiang   Dai Xiaoyu  

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Optical Tamm state (OTS), which exists generally at the interface between metal and dielectric Bragg mirror, has been studied extensively in the visible and near infrared spectra. Nevertheless, OTS in the terahertz region is normally received far less attention. In this paper, we demonstrate the physical mechanism of OTS at the interface between graphene and dielectric Bragg mirror in the terahertz frequency by applying the transfer matrix method and dispersion characteristics. Based on such mechanism, we propose an efficient method that can precisely generate and control OTS at a desired angle and frequency. Moreover, we show that the OTS is dependent on the optical conductivity of graphene, making the graphene-dielectric Bragg mirror to be a good candidate for dynamic tunable OTS device in the THz frequency range.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Tang Jiao   Xu Jiao   Zheng Zhiwei   Dong Jun   Dong Hu   Qian Shenyou   Guo Jun   Jiang Leyong   Xiang Yuanjiang  

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In this paper, we have shown that giant Goos-Hänchen shift of light beam reflected at terahertz frequencies can be achieved by using a composite structure where monolayer graphene is coated on one-dimensional photonic crystal separated by a dielectric slab. This giant Goos-Hänchen shift originates from the enhancement of the electrical field owing to the excitation of optical Tamm states at the interface between the graphene and one-dimensional photonic crystal. It is shown that the Goos-Hänchen shift in this structure can be significantly enlarged negatively and can be switched from negative to positive due to the tunability of graphene’s conductivity. Moreover, the Goos-Hänchen shift of the proposed structure is sensitive to the relaxation time of graphene and the thickness of the top layer, making this structure a good candidate for dynamic tunable optical shift device in terahertz regime.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Xiong Huai   Tang Yongxing   Hu Lili   Li Haiyuan  

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A λ/4–λ/4 broadband antireflective coating is developed using a sol-gel dip coating method. By adding SAR-5 organosilicon resin into a base-catalyzed silica sol top layer and treating at 300°C, a broadband antireflective coating used for blast-shields with a high average transmission of 99.34% (450–950 nm) and good hydrophobicity (with a water contact angle of 119°) was obtained. After being subjected to rubbing 50 times and being maintained at a relative humidity of around 95% for 50 d, the average transmission of the coating decreased by 0.29% and 0.04%, respectively. This indicates that the organically modified silica broadband antireflective coating has good abrasion resistance and humidity stability.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Zhang Yixuan   Gao Chunqing   Wang Qing   Na Quanxin   Zhang Meng   gao mingwei   Huang Shuai  

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A novel 1 kHz single-frequency Q-switched Er:YAG laser pumped by a 1470 nm laser diode (LD) is demonstrated. The 500 ns, 5.52 mJ single-frequency diffraction-limited pulses are obtained by using a ‘Ramp-fire’ injection-seeding technique and an optical feedback architecture. The half-width of the pulse spectrum is measured to be 1.47 MHz by using the heterodyne technique. The beam quality M2 factors are measured to be 1.18 and 1.24 in x and y directions, respectively.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

ZOU Xihua   Li Peixuan   Pan Wei   Yan Lianshan  

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As a key figure-of-merit for high-performance microwave filters, the out-of-band noises rejection is of critical importance in a wide range of applications. This paper overviews the significant advances in the photonic microwave filters (PMFs) having ultra-high rejection ratio for out-of-band noise suppression over the last ten years. Typically, two types of PMFs, the bandpass and bandstop ones, are introduced with fundamental principles, detailed approaches, and then the cutting-edge results for noises rejection. Ultra-high noise rejection ratios of ~80 dB and >60 dB have been demonstrated for single-passband and single-stopband PMFs respectively, which are comparable with the state-of-art electronic filters operating in stringent conditions. These PMSs are also characterized by wide frequency coverage, low frequency-dependent loss, and strong immunity to electromagnetic interference, due to the intrinsic features from advanced photonics technology.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Li Ziqi   Li Rang   Pang Chi   Zhang Yuxia   Yu Haohai   Chen Feng  

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Graphene and other extraordinary two-dimensional materials together with recent advances in optical modulators have set the foundations for the widespread applications of next-generation optoelectronic devices. In this paper, we report on the high-performance fundamentally mode-locked waveguide laser modulated by CVD-grown WSe2 as a saturable absorber. By incorporating WSe2 sample into a monolithic Nd:YVO4 waveguide platform, 6.526 GHz picosecond pulsed laser generation have been achieved at the wavelength of 1 μm with pulse duration as short as 47 ps. This work indicates promising applications of WSe2 for the development of on-chip ultrafast photonics devices.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Yuan Shuai   Wang Lirong   Liu Fengjiang   Zhou Fengquan   Li Min   Xu Hui   Nie Yuan   Nan Junyi   Zeng Heping  

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We report a universal approach based on the surface plasmon resonances (SPRs) attained in filamentation in water doped with gold nanoparticles for enhancing the nonlinear refractive index. The filament-induced supercontinuum spectrum in water overlaps with SPRs of gold nanospheres, which further leads to a modification on the Kerr nonlinear refraction index. In our experiment, the measured nonlinear refractive index (n2) in water doped with gold nanoparticles increases six times as compared with that in pure water. Such enhancement may be useful for filament-induced nonlinear applications with modest incident intensity.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Li Miao   Chen Gui   Leng Jinyong   Chen Jinbao   Li Jinyan  

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In this work, non-isothermal bleaching of Yb-Li co-doped fiber was investigated. The Yb-Li co-doped fiber was beneficial to reduce the photodarkening (PD)-induced excess loss, and had no bad effect on the temperature of thermal bleaching (TB). Photodarkened fibers were bleached with different temperature ramp rates. The higher the ramp rate, the higher the complete bleaching temperature. The activation energy of the bleaching of Yb/Al/Li fiber was calculated by fitting, which was similar to that of Yb-doped fiber. It indicated that the mechanism of mitigating PD by Li co-doping was different from that of TB, and was not subject to temperature.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Li Guangji   Zhang Hongchao   Wang Chengmin   Pan Yunxiang   Lu Jian   Zhou Dayong  

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The photoelectric properties of In_0.3Ga_0.7As solar cell applied in laser wireless power transmission(LWPT) was studied when irradiated by 1070nm continuous(CW) laser of various intensities. The influences of laser intensity on solar cell parameters extracted by pollination algorithm were analyzed quantitatively. Results show that conversion efficiency of the cell rose to the maximum and then decreased rapidly in the laser intensity range of 50-900mW/cm². With higher energy laser irradiation, the rise of ideality factor and reverse saturation current would lead to the degradation of voltage at maximum power point, which was the main reason for the decrease of conversion efficiency. The results provide basis for choosing the appropriate input energy in the case of different transmission systems.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Zhang Qi   Ren Juanjuan   Duan Xueke   Hao He   Gong Qihuang   Gu Ying  

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Enhancing light-matter interaction in cavity quantum electrodynamics has aroused widespread interests in on-chip quantum information processing. Here we propose a hybrid nanotoroid-nanowire system to enhance photon-exciton interaction. A nanoscale gap is formed by placing a dielectric nanowire close to a dielectric nanotoroid, where the coupling coefficient between photon and emitter can achieve 5.55 times of that without nanogap. Meanwhile, the cavity loss and the spontaneous emission of the emitter will remain at small value to guarantee the realization of strong coupling. The method might hold promise for the research of nanophotonics, quantum optics and novel optical devices.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Khan Humayun   Haneef Muhammad   Bakhtawar Bakhtawar  

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We report a theoretical demonstration for the creation of space time holes based on birefringence of reflection, transmission and the Goos H\"{a}chen shifts from a chiral medium. We observed space time holes in the reflection, transmission and their corresponding GH-shifted beams. Two space time holes are clearly detected in the regions of $0<t\leq5\tau_0$ and $-5w\leq y\leq 5w$ as well as in the regions of $-5\tau_0\leq t\leq0$ and $-5w\leq y\leq 5w$. These space time holes hide objects and information contents from observers and hackers. The objects and information contents are completely undetectable, thus events can be cloaked. The results of this paper have potential applications in invisibility of drone technology and secure communication of information in telecom industries.

       PDF全文        Chinese Optics Letters ，2019年第17卷第3期 pp.03      

Fu Zhijie   Wang Qiyu   Wang Zhaoying   Bin Wu   Cheng Bing   Lin Qiang  

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The first Asia-Pacific Comparison of Absolute Gravimeters (APMP.M.G-K1) was organized by the National Institute of Metrology (NIM) of China during from December 21st, 2015 to March 25th, 2016 in Changping, Beijing. Our compact cold atom gravimeter (CCAG) was transported from Hangzhou to Beijing with a long distance of about 1200 km to participate in this comparison. The CCAG is the only one which based on the principle of atom interferometry among all the instruments. The absolute gravity in the indicated three test sites has been measured as requested by the organizer. The sensitivity of our CCAG is estimated to be 90 μGal/√Hz even when the measurements are carried out without any vibration isolation. Besides, the accuracy of this gravimeter has been evaluated to be about 19 μGal by considering the significant system errors. Our results show a good agreement with the given reference value.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Jiang Tian   Miao Runlin   Zhao Jie   Xu Zhongjie   Zhou Tong   Wei Ke   You Jie   Zheng Xin   Wang Zhenyu   Cheng Xiangai  

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Broadband transient reflectivity traces were measured for Bi2Se3 thin films with various substrates via a 400 nm pump-white light probe setup. We have verified the existence of a second Dirac surface state in Bi2Se3 and qualitatively located it by properly analyzing the traces acquired at different probe wavelength. Referring to the band structure of Bi2Se3, the relaxation mechanisms for photo-excited electrons with different energies are also revealed and studied. Our results show a second rise of the transient reflection signal at the time scale of several picosecond. The types of substrate can also significantly affect the dynamics of the rising signal. This phenomenon is attributed to the effect of lattice heating and coherent phonon processes. The mechanism study in this work will benefit the fabrication of high-performance photonic devices based on topological insulators.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Jia Yuechen   Chen Feng  

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Over the last years there has been tremendous progress with compact pulsed lasers based on various solid-state gain media such as crystals and glasses doped with laser-active ions. With the integration of increasingly colorful saturable-absorber materials, these small sources are capable of delivering stable pulses with duration as short as femtosecond and repetition rate exceeding ten gigahertz. These promising sources are known as solid-state waveguide lasers, which have become synonymous with miniaturization, integration, and functionality. This article overviews the progress in the development of passively Q-switched and mode-locked solid-state waveguide lasers employing diverse saturable absorbers. The most commonly used laser configurations, the state-of-the-art waveguide fabrication techniques and the experimental demonstrations of pulsed waveguide lasers are summarized and reviewed. Selected well-noted topics which may shape the future directions in this field are also presented.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

He Zhiwen   Zheng Yang   Liu Hongyan   Li Mingkun   Lu Hua   Zhang Heze   Feng Qingliang   Mao Dong  

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We demonstrate an all-fiber Q-switched cylindrical vector laser based on a black phosphorus saturable absorber and a transverse mode converter. The saturable absorber is prepared by incorporating the polyvinyl alcohol with anti-oxidized black phosphorus nanosheets exfoliated in aqueous poly dimethyldiallyl ammonium chloride solutions. The mode converter is composed of tapered two-mode fiber and single-mode fiber, and it can excite switchable azimuthally and radially polarized beams by modulating the input polarization. By enhancing the pump power from 64.68 mW to 174.82 mW, the repetition rate of Q-switched azimuthally/radially polarized laser enlarges from 16.72/19.25 kHz to 30.71/37.82 kHz.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

wang cong   Peng Qian   Xin Linlin   Liu Jie  

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Two-dimensional (2D) materials have attracted intense attention in photonics and optoelectronics for their excellent nonlinear characteristics and is applied for the generation of laser pulse. Here, a active-passive Nd:GdVO4 1.3 μm laser is realized by using an acousto-optic modulator and gold nanobipyramids absorber. The pulse width of 150.5 ns is obtained in the doubly Q-switched laser. The compression ratio and enhancement time are 82.6 % and 16. The doubly Q-switched technology compresses the pulse width, improves the peak power and stabilizes the pulse, illustrating the doubly modulation technology opens the door of controllable ultrafast lasers based on 2D materials.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Liu Beiyun   You Congya   Zhao Chen   Shen Gaoliang   Liu Yawei   Li Yufo   Yan Hui   Zhang Yongzhe  

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Graphene, as a novel 2D material, has attracted great of interest in optoelectronics owing to its high carrier mobility and broadband absorption. However, Graphene photodetector exhibits low photoresponsivity because of its low light absorption. In this work, we designed a graphene/MoSe₂ heterostructure photodetector, which exhibits photoresponse ranging from visible to near infrared and an ultrahigh photoresponsivity up to 1:3× 10⁴A/W at 550nm. The electron-hole pairs are excited in a few layered MoSe₂ and separaed by the built-in electric field. Large number of electrons shifted to graphene while holes remain in the MoSe₂, which creates a photogating effect. Moreover, the lifetime of electrons can be greatly extended because the trap of holes in MoSe₂ delays the recombination in the circuit. This photodetector represents powerful performance in the near-infrared wavelength regime and have the potential application in many area.

       PDF全文        Chinese Optics Letters ，2019年第17卷第2期 pp.02      

Cai Yuancheng   Ling Yun   Gao Xiang   Xu Bo   Qiu Kun  

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We propose and investigate the use of Kramers–Kronig (KK) receiver in single sideband orthogonal frequency division multiplexing radio over fiber (SSB-OFDM-RoF) link based on optical remote heterodyne solution. This scheme is effective in eliminating the signal-to-signal beating interference (SSBI) introduced by square-law detection of photo-detector (PD) in SSB-OFDM-RoF link. We extensively studied the influences of different carrier-to-signal power ratios (CSPRs), laser linewidths and transmission distances on our proposed scheme. It is proved that the KK-based receiver can reduce optimal CSPR by more than 5 dB and provide about 1.1 dB gain over the conventional mixer-based receiver scheme with CSPR of 11 dB after 75 km fiber transmission.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Li Jiakun   Feng Qibo   Bao Chuanchen   Zhang Bin  

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We report a method for simultaneously and directly measuring all the six-degrees-of-freedom motion errors of a rotary axis. Such method combines the principles of laser interferometry and laser collimation measurement. One reference rotary axis and two retro-reflectors are used to achieve simultaneous sensitivity to all six errors in a full-circle measuring range. As no separation models are required, our method is capable to dynamically measure these errors in real time and conveniently determine the origin of the errors. An automatic measuring device was built. The effectiveness of our method is experimentally demonstrated.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Li Chun   Leng Yuxin   Huo Jinjin  

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This study investigates the applicability of a few-layer structure ReSe2 as a saturable absorber (SA) for demonstrating a passively Q-switched pulse laser. The ReSe2 SA had a modulation depth of 6.86%. The Q-switched experiment was successful in delivering a maximum average output power of 180 mW at the wavelength of 1906.5 nm. The optimal pulse train had a pulse width of 1.61 μs and a repetition rate of 28.78 kHz. The experiment results verify that the few-layer structure ReSe2 could behave as an excellent SA at all-solid-state lasers, increasing the selection of SA at near 2 μm laser.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Kharmyssov Chingis   Ko Match   Kim Jong R.  

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We propose a fast and accurate automated algorithm to segment retinal pigment epithelium and internal limiting membrane layer from spectral-domain optical coherence tomography (SDOCT) B-scans images. A hybrid algorithm, which combines intensity thresholding and graph-based algorithms, was used to process and analyze SDOCT radial scans (a hundred and twenty B-scans) images obtained from twenty patients. The relative difference in position of the layers segmented by the proposed hybrid algorithm and by clinical expert was 1.49% ± 0.01%. The processing time of the hybrid algorithm was 9.3 s for six B-scans. The Dice’s coefficient of the hybrid algorithm was 96.7%±1.6%. The proposed hybrid algorithm for the segmentation of SDOCT images had good agreement with manual segmentation and reduced processing time.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Zhou Yong   Gao Panyun   Zhang Xiu   Wang Peng   Chen Liang   Gao Weiqing  

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We propose a switchable multi-wavelength erbium-doped fiber laser based on a four-mode fiber Bragg grating. The four-mode fiber Bragg grating is fabricated in a hydrogen pre-loaded fiber by the phase mask method which can support four linearly polarized modes around 1550 nm. The five operation wavelengths are at 1547.5, 1546.8, 1546.0, 1545.1 and 1544.2 nm, respectively. Through adjusting the polarization state and the lateral offset coupling in cavity, the laser can be switched into the operation state of single, dual or triple wavelengths. The proposed laser has the advantages of simple configuration, stable operation and easy adjustment.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Meng Xin   Yang Zhongming   Du Jinyu   Fan Guobin  

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A double-pass grating imaging spectrometer is proposed and demonstrated. The traditional entrance slit is replaced by a middle reflective slit which is used as a spectral filter rather than a spatial filter. The light from the scene passes through the same dispersive grating twice. The full image of the scene can be obtained with snapshot. Therefore the stripe noise and images distortion caused by image mosaicking can be eliminated. Besides, the target is easier to be captured and focused just like using a camera. This method can be used to obtain clearer spectral images of the scene conveniently and quickly.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Bai Zhengyang   Zhang Qi   Huang Guoxiang  

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Electromagnetically induced transparency (EIT), a typical quantum interference effect, has been extensively investigated in coherent atomic gases. In recent years, it has been recognized that plasmonic analog of atomic EIT, called plasmon-induced transparency (PIT), is a fruitful platform for the study of EIT-like propagation and interaction of plasmonic polaritons. Many proposals have been presented for realizing PIT in various metamaterials, which possess many unique characters, including the suppression of absorption of electromagnetic radiation, the reduction of propagation velocity, etc. Especially, nonlinear PIT metamaterials, obtained usually by embedding nonlinear elements into meta-atoms, can be used to acquire enhanced Kerr effect resulted from the resonant coupling between radiation and the meta-atoms, and to actively manipulate structural and dynamical properties of plasmonic metamaterials. In this article, we review recent research progress on nonlinear PIT metamaterials, elucidate their interesting properties and promising applications. In particular, we give a detailed description on the propagation and interaction of nonlinear plasmonic polaritons in metamaterials via PIT, which are promising for chip-scale applications in information processing and transmission.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Ma Huiliang   Jia Xin-Hong   Lin Kai   Xu Cong  

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For Brillouin optical time-domain analysis (BOTDA) based on distributed Brillouin amplification (DBA), constant Brillouin response achieved by the exponentially variable bandwidth/intensity pump modulation suffers from the much lower pumping efficiency for long-range sensing, which counterbalances the merit of DBA. In this letter, pump modulation by multiple constant bandwidths was proposed and demonstrated. ~98.9 km sensing with ~5 m spatial resolution and no use of optical pulse coding (OPC) was achieved by ~8 dBm Brillouin pump, which is lower by ~9 dB in theory by comparison with exponentially increased bandwidth modulation. Compared with traditional DBA-BOTDA, signal-to-noise ratio (SNR) enhancement with > 4.6 dB was obtained. The flattened standard deviation (STD) of Brillouin frequency shift (BFS) (less than ~2 MHz) along the whole fiber was demonstrated.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Amin Md Ziaul  

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In erbium doped fiber amplifier (EDFA), erbium ions act as a three-level system. Therefore, much higher pump energy is required to achieve the population inversion in an erbium doped fiber (EDF). This higher pump energy requirement complicates the efficient design of an EDFA. However, efficient use of the pump power can improve the EDFA performance. The improved performance of an EDFA can be obtained by reducing the doping radius of the EDF. A smaller doping radius increases pump-dopant interactions and subsequently increases the pumpphoton conversion efficiency. Decreasing the doping radius allows a larger proportion of dopant ions, which are concentrated near the core, to interact with the highest pump intensity. However, decreasing the doping radius beyond a certain limit will bring the dopant ions much closer and introduce detrimental ionion interaction effects. In this paper, we show that an optimal doping radius in EDF can provide the best gain performance. Moreover, we have simulated the well-known numerical aperture (NA) effects on EDFA gain performance to support our claim.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Zhang Zexia   Chang Jun   Ren Hongxi   Fan Kaiyuan  

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This letter proposes a snapshot imaging spectrometer, which obtains the spectral information and spatial information in one “shot”. The device proposed can achieve the datacube size of 21*29*40 between the waveband 400-800nm. The core element of this system is the microlens array, which contains 60*60 microlens in a square arrangement, each microlens has an aperture of 125μmX125μm, and F number is 15. The microlens array is mounted in a rotation mount which provides 360° of rotation around the optical axis to maximize the spectral resolution. The final resolution of the system is about 10nm.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Zhang Faxiang   Wang Chang   Zhang Xiaolei   Jiang Shaodong   Ni Jiasheng   Peng Gangding  

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We present a highly sensitive fiber Bragg grating (FBG) based microphone with a flat response and static pressure equalization. A very high dynamic sensitivity is achieved by a pressure sensing structure based on a carbon fiber diaphragm. Static pressure equalization is realized by a balance structure with a capillary glass tube. The resonances of the sensor are suppressed by air damping structures, and a broadened flat response is achieved. Acoustic-solid interaction model was used to analyze the response characteristics of the microphone. A sensor prototype was produced and tested, and the results are well consistent with the design. The tested sensitivity was -10 dB re 1 pm/Pa from 10 Hz to 2.5 kHz, with a fluctuation of less than ±1.5 dB. Combined with the PGC (Phase Generated Carrier)-based coherent detection scheme, the microphone can achieve a sound resolution of mPa level. The static pressure sensitivity is measured to be -0.27 pm/atm, which is 100 dB lower than the dynamic sensitivity.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Diao Zhihui   Kong L   Yan Junliang   Guo Junda   Liu Xiaofeng   Xuan Li   Yu Lei  

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In this letter, we present an electrically tunable holographic waveguide display (HWD) based on two slanted holographic polymer dispersed liquid crystal (HPDLC) gratings. Experimental results show that a see-through effect is obtained in the HWD that both the display light from HWD and the ambient light can be clearly seen simultaneously. By applying an external electric field, the output intensity of the display light can be modulated, which is attributed to the field-induced rotation of the liquid crystal molecules in the two HPDLC gratings. We also show that this electrically tunable performance enables the HWD to adapt to different ambient light condition. This study provides some ideas towards the development of HWD and its application in augmented reality.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Hu Jinhua   Fu Jia   Liu Xiuhong   Ren DanPing   Zhao JiJun   Huang Yongqing  

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We present a perfect graphene absorber with compound waveguide grating at near infrared. The analytical approach is mainly based on the coupled leaky mode theory, which turns the design of absorber to finding out the required leaky modes supported by the grating structure. Perfect absorption occurs only when the radiative loss of the leaky mode match the intrinsic absorption loss, which is also named as critical coupling condition. Furthermore, we also demonstrate that the critical coupling of the system can be robustly controlled, and the perfect absorption wavelength can be easily tuned by adjusting the parameters of compound waveguide grating.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Sun Fangyuan   Zhao Yufei   Shu Shili   Hou Guanyu   Lu Huanyu   Zhang Xin   Wang Lijie   Tian Sicong   Tong Cunzhu   Wang Lijun  

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A modified spectral beam combining (SBC) approach based on double asymmetrical filters was proposed. By using this scheme, the high-order lateral modes at the edge of the far-field pattern can be suppressed in the external cavity, and the beam quality in the slow-axis direction was improved from 16.1 to 13.4 compared to the conventional SBC. In the meanwhile, the electrical-to-optical efficiency from the modified SBC was more than 40% with an output power of 34.1 W, which was similar to that of the conventional SBC.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Li Guiyun   Gu Liyuan   Hu Jingpei   Zhu Linglin   zeng Aijun   Huang Huijie  

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Single layer graphene deposited on the metal substrate can hardly be imaged by the optical microscope. In this paper, a large field-of-view imaging ellipsometer is introduced to image the single layer graphene which is deposited on metal substrate. By adjusting the polarizer and the analyzer of imaging ellipsometer, the light reflected from surfaces of either single layer graphene or Au film substrate can extinguish, respectively. Thus the single layer graphene can be imaged correspondingly under brightfield or darkfield imaging mode. The method can be applied to imaging large-area graphene on metal substrate.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Zhao Huijie   Xing Jian   Gu Xingfa   Jia Guorui  

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A method for calculating atmospheric parameters measurement accuracy requirement based on polarized reflectance retrieval is proposed. The at-sensor polarization states with different atmospheric parameters content are simulated based on atmospheric radiative transfer model in order to select the key parameter affecting the polarization observation. Accuracy requirement of atmospheric parameters is derived through the polarized reflectance retrieval method. Experiment results show that retrieval accuracy of polarized reflectance of typical ground objects can be up to 90%. And the atmospheric parameters measurement accuracy requirement when the retrieval accuracy is more than 75% is derived.

       PDF全文        Chinese Optics Letters ，2019年第17卷第1期 pp.01      

Shi Junkai   Li Yao   Gao Shuyuan   Pan Yingling   Wang Guoming   Ji Rongyi   Zhou Weihu  

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In this paper, we report on a novel architecture for self-starting mode-locked figure-8 erbium-doped fiber laser using a loss-imbalanced nonlinear optical loop mirror (NOLM) with a bidirectional output coupler. All polarization-maintaining structure is adopted. A 2×2 optical coupler with splitting ratio of 50:50 is used at the junction to form a NOLM. Another coupler with splitting ratio of 10:90 is introduced at one end of fiber loop. The 10:90 coupler plays two roles: power attenuator and bidirectional output coupler. This architecture can achieve both large modulation depth and good self-starting ability simultaneously. With this architecture, the self-starting mode locking operation is achieved easily with pump power above threshold. The clockwise and counter-clockwise mode locked output powers are 10.1 mW and 10.3 mW, respectively, with the repetition rate of 3.63 MHz. The spectral bandwidths of the clockwise and counter-clockwise mode locked output pulses are 7.4 nm and 2.9 nm, and the corresponding pulse widths of the direct outputs are 530.6 fs and 1.55 ps, respectively.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Dai Bo   Wang Huansi   Xu Qiao   Li Zhenqing   Tao Chunxian   Zhang Dawei  

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A rapid and cost-effective method for fabricating mini lens arrays is proposed. The lenses are made of silicone oil droplets and filled inside a polydimethylsiloxane (PDMS) elastomer. The lens array of different initial focal length and aperture can be fabricated by using the droplets of different volume. Due to good elastic behavior of PDMS, the droplet lenses can be flexibly deformed and focal length and numerical aperture can be tuned by applying an external force on the PDMS elastomer. Furthermore, an apparatus for focal length tuning is designed and employed in the imaging system.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Yu Yi   Gong Shaobo   Xu Min   Yuan Boda   Wu Yifan   Nie Lin   Ke Rui   Ye Minyou   Duan Xuru  

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System validation and density fluctuation calibration of Phase Contrast Imaging (PCI) on HL-2A tokamakare presented. Signals from different channels show not only a pronounced modulation of incident laser beam induced by sound wave but also an excellent magnification and low image distortion of optics. Frequency-wavenumber spectrum is achieved by using two-dimensional Fourier transform of time series signals. Conversion relationship between detected signal amplitude and chord integral plasma density fluctuation is 2.35×1013m-2/mV, which promises a suitable signal level at the order of Volts of the PCI in typical HL-2A discharges.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Xie Hongqiang   Li Guihua   Yao Jinping   Chu Wei   Chen Zhiming   Cheng Ya  

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We report on an experimental investigation on the dynamic decoherence process of molecular rotational wavepackets during femtosecond laser filamentation based on time-dependent mean wavelength shifts of a weak probe pulse. Details of periodic revival structures of transient alignment can be readily obtained from the measured shifted spectra due to the periodic modulation of molecular refractive index. Using the method, we measured the decoherence lifetimes of molecular rotational wavepackets in N₂ and O₂ under different experimental conditions. Our results indicate that the decoherence lifetimes of molecular rotational wavepackets are primarily determined by the relative population of rotational states in the wave packet and intermolecular collisions, rather than the focusing intensity.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Ahmad Harith   Aidit Siti Nabila   Ing Ooi   Cheak Tiu  

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The interest in tunable ultrafast fiber lasers operating at the 1.3 µm region has seen a significant increase due to ever rising demands for bandwidth and the zero-dispersion characteristic of silica fiber. In this work, a tunable mode-locked Praseodymium-doped fluoride fiber (PDFF) laser using single-walled carbon nanotubes (SWCNT) as a saturable absorber (SA) is demonstrated. The mode-locked pulses are generated at center wavelength of 1302 nm with a pulse repetition rate of 5.92 MHz, and pulse width of 1.13 ps. The tunability of the mode-locked PDFF laser covers a tuning range of 11 nm.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Yu Lei   Zou Weiwen   Yang Guang   Li Xinwan   Chen Jianping  

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This Letter theoretically and experimentally studies the response of photonic switching in a channel-interleaved photonic analog-to-digital converter (PADC) with high sampling rate and wide input frequency range. A figure of merit (FoM) is introduced to evaluate the switching response of the PADC when a dual-output Mach-Zehnder modulator (MZM) is served as the photonic switch to parallelize the sampled pulse train into two channels. After the optimization of the FoM and utilization of channel-mismatch compensation algorithm, the system bandwidth of PADC is expanded and the signal-to-distortion ratio (SDR) is enhanced.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Shi Qianqian   Zhang Yan   Wang KunPeng   Wang Chenglin   Zhao Peng  

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The impact pendulum and torsion pendulum are mostly applied in impulse coupling experiments of high energy laser irradiation on space debris. It is difficult to achieve multi-pulse experiment and thus hard to analyze the multi-pulse impulse coupling effect. Here, we designed a new recoil impulse experimental measurement system of non-contact, multi-degree of freedom and multi-pulse irradiation is designed. The system used a low-pressure and low-temperature vacuum chamber to simulate the space environment, the pinning effect of magnetic levitation to achieve aluminum target suspension and high-speed cameras to record the displacement over time to calculate the impulse of target. Then the impulse coupling experiment of multi-pulse laser irradiation on aluminum target was performed. The result shows that the multi-pulse impulse coupling effect is not the linear accumulation of coupling results by every single pulse and mul-ti-pulse coefficient decreases with the increase of the number of pulses, and eventually stabilizes as the decrease getting smaller and smaller.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

xia kaiye   Zhai Xiaohui   Xie Zhaoheng   Zhou Kun   Feng Yutao   Zhang Guangjie   Li Changhui  

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Photoacoustic (PA) tomography (PAT) breaks the barrier for high resolution optical imaging in strong light scattering medium, having a great potential for both clinical implementation and small animal studies. However, many organs and tissues lack enough PA contrast or even hinder the propagation of PA waves. Therefore, it is challenging to interpret pure PAT images, especially PA three-dimensional (3D) images for deep tissues without enough structural information. To overcome this limitation, in this study, we integrated PAT with X-ray computed tomography (CT) in a standalone system. PAT provides optical contrast and CT gives anatomical information. We performed agar, tissue phantom and animal studies, and the results demonstrated that PAT/CT imaging system can provide accurate spatial registration of important complementary contrasts.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Zhang Yumin   Ren Yue   Dong Mingli   Meng Fanyong   zhu lianqing  

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The Letter reports the thermal stability and strain response of Fabry-Perot (FP) cavity under different high temperatures. The FP cavity was made by thermal regeneration of two identical cascaded fiber Bragg gratings (FBGs). It is demonstrated that the FP cavity is capable of measuring temperature from 300 °C to 900 °C, with a temperature sensitivity of 15.97 pm/°C. The elongation of fiber was observed through the drifted Bragg wavelength at 700 °C or above when weight was loaded. The elongation was further inferred by the slight change in interference spectra of FP cavity at 900 °C.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

yan lulu   zhang yanyan   tai zhaoyang   zhang pan   zhang xiaofei   guo wenge   Zhang Shougang   jiang haifeng  

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By taking advantage of PDH frequency stabilization technique, frequency instability of most ultrastable laser systems is mainly limited by the thermal noise of the high reflection mirrors. In this letter, we demonstrate a proposal of making an ultrastable laser referenced to a multi-cavity, enabling a lower thermal noise limit due to the larger equivalent beam size. The multi-cavity consists of a few pairs of mirrors and a common spacer. One can stabilize the laser frequencies on these cavities, and average the laser frequencies with an optical synthesizer. In comparison with a single cavity system, relative frequency instability of the synthesized laser can be improved by a factor of the squire root of the cavity number (n). To proof this proposal, we perform an experiment to simulate a two-cavity system with two independent ultrastable lasers. These laser exhibits a frequency instability at 7E-16 for short term. Experimental results show that the relative frequency instability (Allan deviation of Δν/ν) of the synthesized laser is 5E-16 improved by a factor of √2 from a signal cavity stabilized laser. The measured noise effect of optical synthesizing is at E-17 level limited by synchronization of frequency counters, it reaches E-18 level while the lasers have lower noise level. This technique is compatible with other techniques; thus, it can gain a factor of √n on the frequency instability based on the current ultrastable lasers at the state-of-the-art level.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Liu Jing   Li Lei   Shi Xiangchun   chen rufeng   Wang Jianlei   Chen Weibiao  

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A high beam quality diode-pumped Nd:YAG active mirror laser amplifier was demonstrated. The size of Nd:YAG crystal was 48 mm x 42 mm x 11 mm with 0.6 at.% doped. When the pump energy was 26.8 J and the input energy was 0.3 J, the output pulse energy reached 5.4 J, the pulse width of 11.3 ns at 5 Hz repetition rate was obtained for the two gain modules in three-pass amplification, corresponding optical-to-optical efficiency was 21.2%. The beam quality was measured as M_x^2=2.48, and M_y^2=2.43 in horizontal and vertical directions, respectively.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Hu Jiashun   Zhang Zaichen   Wu Liang   Dang Jian   Zhu Guanghao  

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The average bit-error rate performance is studied for a coherent free-space optical communication system employing differentially encoded quadrature phase shift keying with the Mth-power phase estimation method. A closed-form expression, considering the combined effects of the M turbulence fading, pointing errors and phase estimation errors, is derived in terms of the Meijer's G function. Numerical and Monte Carlo simulation results are presented to verify the derived expression.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Barcelo-Chong Arturo   Estrada-Potrillo Brian   Canales-Benavides Arturo   Lopez Aguayo Servando  

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We report the generation of asymmetric Mathieu optical lattices: invariant intensity optical profiles that can described by three parameters. The first one describes the amount of ellipticity, the second one takes into account the degree of asymmetry of the profile, and the third parameter denotes the angular position where is localized the respective asymmetry. We propose a simple angular spectrum to generate these nondiffracting beams, and we report how changes their distribution of power and orbital angular momentum in function of their ellipticity and degree of asymmetry. We confirm the existence of these invariant beams by propagation in an experimental setup.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Hu Dongxia   Tao Yudong   Ma Jingui   Wang Jing   Zhu Heyuan   Qian Liejia  

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Quasi-parametric chirped-pulse amplification (QPCPA) can improve the signal amplification efficiency and stability by inhibiting the back conversion, in which the idler absorption plays a critical role. This paper theoretically studies the impacts of idler absorption on the QPCPA performance in both the small-signal and saturation regimes. We demonstrate that there exists an optimal idler absorption that enables the achievement of maximum pump depletion within a minimum crystal length. To overcome the reduction in small-signal gain induced by idler absorption, the configuration of gradient idler absorption is proposed and demonstrated as a superior alternative to constant idler absorption. The results provide guidelines to the design of state-of-the-art QPCPA lasers.

       PDF全文        Chinese Optics Letters ，2018年第16卷第12期 pp.12      

Zhang Zhiming   Wei Wei   Tang Liqin   Yang Jie   Guo Jiewei   Ding Lei   Li Yigang  

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An all fiber femtosecond vortex laser based on common fiber components is constructed. It can produce femtosecond orbital angular momentum modes whose pulse width of time is 398fs. The topological charge of output OAM modes from this setup can be adjusted among 0, +1, -1 easily while it is also easy to convert between continuous OAM modes and pulse OAM modes.

       PDF全文        Chinese Optics Letters ，2018年第16卷第11期 pp.11      

Yao Jie   Yu Ya-fei   Zhang Zhiming  

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We introduce a Casimir force in a conventional optomechanical system to study the high-order sideband generation. In this system, a nanosphere is placed nearby the moveable mirror of the conventional optomechanical system. The moveable mirror is coupled to the cavity field and the nanosphere by the optomechanical interaction and the Casimir interaction, respectively. We find that the amplitude and cutoff order of the high-order sideband can be enhanced by decreasing the sphere-mirror separation ( increasing the Casimir force) and increasing the optomechanical coupling strength. Our proposal provides an alternative method for generating the high-order sidebands, and for measuring the Casimir force.

       PDF全文        Chinese Optics Letters ，2018年第16卷第11期 pp.11      

Wang Feili   Lou Cibo   Liang Yi  

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We numerically investigate the propagation properties of ring Airy Gaussian beams (RAGBs) with cosine modulated optical vortices (CMOV). In comparison to the common RAGBs without any modulation, the dynamic propagation of RAGBs with CMOV exhibits a unique feature: the rings of RAGBs with CMOV will gradually shrink into several main lobes with the increase of the propagation distance. The number of lobes and the peak intensity of each lobe are determined by the factors of cosine modulated function. By designing the initial phase, we can easily change the transversal location of the peak intensity. Our results may find potential applications in optical manipulations.

       PDF全文        Chinese Optics Letters ，2018年第16卷第11期 pp.11      

Cui Peng   Zhang Wentao   Song Ying  

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In this paper, a vertical-pendulum-based inclinometer based on Fiber Bragg Grating Fabry-Perot (FBG-FP) cavity is proposed. A low-damping rotation structure is used to reduce the mechanical frictions of the pendulum system and induce wavelength shift of FBG-FPs. We find that the sensitivity can be maximized by optimizing the parameters of the inclinometer. Using high-resolution demodulation system, a sensitivity of 179.9 pm/° and a resolution better than 2.0×10-2 ″ can be achieved. Experiments also show that the proposed inclinometer has good linearity and repeatability.

       PDF全文        Chinese Optics Letters ，2018年第16卷第11期 pp.11      

Gao Wanli   Liu Guanyu   Zhang Zhigang  

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44.6 fs pulses from a 257 MHz, mode-locked non-PM Er-doped fiber laser based on biased nonlinear amplifying loop mirror (NALM) is reported. The output power is 104 mW and the single pulse energy is 0.4 nJ. The minimum pulse duration of the direct output is 44.6 fs, which is the shortest in this kind of laser.

       PDF全文        Chinese Optics Letters ，2018年第16卷第11期 pp.11      

Deng Suhui   Xiao Yiping   Hu Jie   Chen Jianfang   Wang Yuhao   Liu Mingping  

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The fluorescence from out-of-focus region excited by the side lobes of Bessel beam is the major concerns for the light-sheet fluorescence microscopy (LSFM) with Bessel beam plane illumination. Here, we propose a method of applying the subtractive imaging to overcome the limitation of the conventional LSFM with Bessel beam plane illumination. In the proposed method, the sample is imaged twice by line-scanning using the extended solid Bessel beam and the ring-like Bessel beam. By subtracting between the two images with similar out-of focus blur, the improved image quality with the suppression of the Bessel beam side lobes and enhanced sectioning ability with improved contrast is demonstrated.

       PDF全文        Chinese Optics Letters ，2018年第16卷第11期 pp.11      

Kang Kai   Zhang Liangliang   Wu Tong   Li Kai   Zhang Cunlin  

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We report the terahertz (THz) wave generation from single color scheme modulated by pre-ionized air plasma via an orthogonal pumping geometry. It is found that the amplitude of the THz signal generated by the pump beam tends to decrease gradually with the increase of the modulation power. We believe that the ponderomotive force plays an important role in the process of the interaction between the pump beam and pre-ionization beam. The hydrostatic state of the electrostatic separation field caused by modulation beam will directly affect the generation efficiency of the THz wave. Our results contribute to further understanding of the theoretical mechanism and expanding of the practical applications of terahertz THz wave generation and modulation.

       PDF全文        Chinese Optics Letters ，2018年第16卷第11期 pp.11      

tianbo zhao   fenglan fan   ying liu   yifan hong   jinliang zang   guoguo kang   Tan Xiaodi  

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A novel composite materials are synthesized by incorporating N-acryloylmorpholine (ACMO) in highly-concentrated phenanthrenequinone (PQ) doped poly-(methyl methacrylate) (PMMA). The photosensitizer concentration of PQ was increased from 0.7wt% to 1.8wt%. The doping of ACMO component results in a higher diffraction efficiency and photosensitivity than typical PQ/PMMA system. The enhanced performance of material may stem from the ACMO molecules which might open a new route for improving the holographic performance of PQ/PMMA photopolymer..

       PDF全文        Chinese Optics Letters ，2018年第16卷第11期 pp.11