Wang Fangyu   Yuan Yuhao   Sun Qiang   Dai Ming   Ai Li   Lu Fake  

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We report on two strategies to design and implement the galvanometer-based laser-scanning mechanisms for the realization of reflection confocal microscopy (RCM) and stimulated Raman scattering (SRS) microscopy systems. The RCM system uses a resonant galvanometer scanner driven by a home-built FPGA circuit with a novel dual-trigger mode and a home-built high-speed data acquisition card. The SRS system uses linear galvanometers with commercially available modules. We demonstrate video-rate high-resolution imaging at 11 frames per second (fps) of in vivo human skin with the RCM system and label-free biomolecular imaging of cancer cells with the SRS system. A comparison of the two strategies for controlling galvanometer scanners provides scientific and technical reference for future design and commercialization of various laser scanning microscopes using galvanometers.

       PDF全文        Chinese Optics Letters ，2020年第18卷第12期 pp.12      

Wang Rui   Xu Shaofu   Chen Jianping   Zou Weiwen  

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We demonstrate a photonic architecture to enable the separation of ultra-wideband signals. The architecture consists of a channel-interleaved photonic analog-to-digital converter (PADC) and a dilated fully convolutional network (DFCN). The aim of the PADC is to perform ultra-wideband signal acquisition, which introduces the mixing of signals between different frequency bands. To alleviate the interference among wideband signals, the DFCN is applied to reconstruct the waveform of the target signal from the ultra-wideband mixed signals in the time domain. The channel-interleaved PADC provides a wide spectrum reception capability. Relying on the DFCN reconstruction algorithm, the ultra-wideband signals which are originally mixed up are effectively separated. Additionally, experimental results show that the DFCN reconstruction algorithm improves the average bit error rate (BER) by nearly three orders compared with that without the algorithm.

       PDF全文        Chinese Optics Letters ，2020年第18卷第12期 pp.12      

Ozeki Yasuyuki  

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The recent development of stimulated Raman scattering (SRS) microscopy allows for highly sensitive biological imaging with molecular vibrational contrast, opening up a variety of applications including label-free imaging, metabolic imaging, and super-multiplex imaging. This paper introduces the principle of SRS microscopy and the methods of multicolor SRS imaging, and describes an overview of biomedical applications.

       PDF全文        Chinese Optics Letters ，2020年第18卷第12期 pp.12      

Garza-Rivera Anel   Gomez-Correa J. E.   Renero-Carrillo Francisco   Treviño-Gutierrez Juan   Coello-Cardenas Victor  

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In this paper, a Gabor Superlens with variable focus is presented. This configuration uses tunable liquid lenses in the third microlens array of the Gabor Superlens. By applying voltage, the radius of curvature of the micro-tunable doublet arrays changes, and the Gabor conditions are fulfilled at different focal planes. As a consequence, the magnification of the image at the focal planes changes and a zoom effect is observed. The marginal depth plane for this system goes from 0.86 to 0.89 mm. The optical simulation, the calculations and the results of the simulated optical system performance are presented.

       PDF全文        Chinese Optics Letters ，2020年第18卷第12期 pp.12      

Nakamura Akinao   Mizuta Tomoki   Shimotsuma Yasuhiko   Sakakura Masaaki   Otobe Tomohito   Shimizu Masahiro   Miura Kiyotaka  

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Suppression of stress and crack generation during picosecond laser processing in transparent brittle material such as glass was successfully demonstrated by the picosecond laser pulse with temporal energy modulation. The origin of deterioration in processing accuracy could be interpreted in terms of the discontinuous movement of plasma in the vicinity of focus. To reveal the effectiveness of the temporal energy modulation for smooth machining, such plasma motion was simulated by FDTD. Furthermore, the photoinduced birefringence has been also observed by using high speed polarization camera.

       PDF全文        Chinese Optics Letters ，2020年第18卷第12期 pp.12      

Sheng Jie   Xie Jianlan   Liu Jianjun  

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Based on the triangular lattice two-dimensional photonic crystal (PC), the lattice spacing along the transverse direction to propagation is altered and a gradient PC (GPC) flat lens is designed. The band structures and equal frequency curves (EFCs) of the GPC are calculated, then the imaging mechanism and feasibility are analyzed. The imaging characteristics of the GPC flat lens is investigated. It is observed that the GPC can achieve multiple types of super-resolution imaging for point source. This GPC lens is allowed to be applied to imaging and other fields such as filtering and sensing.

       PDF全文        Chinese Optics Letters ，2020年第18卷第12期 pp.12      

Shang Kejun   Lei Ming   Xiang Qiang   Na Yonglin   Zhang Lizhe   Yu Huaiyong  

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We present a near-navigation grade interferometric fiber optic (IFOG) based on integrated optical chip (IOC). The chip comprises a light source, a photodiodes and a 3-dB coupler within an area of 48 mm2. By interrogating with a integrated optical modulator (IOM), a small diameter sensing coil, the IFOG is realized. This allows for a significant reduction in size, weight, power consumption and cost (SWaP-C). Preliminary performance data of a gyro prototype exhibits 0.018 deg/h bias stability.

       PDF全文        Chinese Optics Letters ，2020年第18卷第12期 pp.12      

Nie Liming   Duan Fei   Ma Haosong   Zhang Jinde   Li Shi   Li Honghui   Wu Zhiyou   Hong Fengqiu   Zeng Lvming  

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Photoacoustic imaging has been developed to image the immune study at macro-scale. Macrophages play diverse roles in the acute response to infection and tissue repair. However, macrophages activities in acute inflammation at microscopic level still remain challenging. In this work, we proposed optical-resolution photoacoustic microscopy to promptly monitor the labeled macrophages activities in normal and inflammatory groups. The result showed that many labeled macrophages emerged around the vessels firstly, then exuded into tissue and finally disappeared in inflammatory group injected with labeled macrophages. In summary, our method allows to exactly image and track the immune cells of inflammatory diseases.

       PDF全文        Chinese Optics Letters ，2020年第18卷第12期 pp.12      

Niu Yunfei   Yang Lei   dongjie guo   Chen Yan   Li Xiaoyang   Zhao Gang   Hu Xiaopeng  

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Abstract: We report efficient generation of 671-nm red light based on quasi-phase-matched second harmonic generation of 1342 nm in LiNbO₃ waveguides. The design method and fabrication process of the high-quality annealed proton-exchanged periodically poled channel waveguides were presented. Continuous-wave 1.71 mW red light was obtained with a single-pass conversion efficiency of 47%·W^-1·cm^-2, which is 88% that of the theoretical value. While for 1 mW quasi-continuous laser input, the conversion efficiency reached up to 60%. Our results indicate that annealed proton-exchanged periodically poled LiNbO₃ waveguide is promising for high-efficiency and low power consumption nonlinear generation of visible light.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Wang Chaofan   Li Guoqiang   Hu Fangchen   Zhao Yiheng   Jia Junlian   Zou Peng   Lu Qiuyi   Chen Jiang   Li Zhongya   Chi Nan  

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Visible light communication (VLC) shows great potential in Internet of Vehicle (IOV) applications. A single-input multi-output (SIMO) visible light communication (VLC) system for Vehicle to Everything (V2X) is proposed and demonstrated. A commercial car headlight is used as transmitter. With a self-designed 2×2 PIN array, 4 independent signals are received and equalized by deep-neural-networks (DNN) post-equalizers respectively. Maximum-ratio combining (MRC) brings signal-noise ratio (SNR) and data rate gain. The transmission data rate reaches 1.25Gb/s at 1m and exceeds 1Gb/s at 4m. To the best of our knowledge, it is the first-time demonstration of beyond 1Gb/s employing a commercial car headlight.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Zhang Tianqi   Wang Mudong   Xue Yang   Xu Jinlong   Xie Zhenda   Zhu Shining  

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We demonstrated the efficient Plasmon-induced nonlinear absorption of liquid metal GaInSn nanospheres prepared by a facile liquid-phase method. With GaInSn as saturable absorbers, passively Q-switching operation was obtained at both 1.3 and 2 μm. The pulse width of 32 ns was achieved at 1.3 μm with repetition rate of 44 kHz, single pulse energy of 51.9 μJ and output power of 425 mW. Meanwhile, 510 ns and 92 kHz pulses with energy of 36.1 μJ and output power of 2.48 W were obtained at 2 μm. This work provides the potential of liquid metal for improving metal functions and flexible optical devices.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Peng Mian   Bai Li  

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Nonsequential double ionization (NSDI) of noble gas atoms in counter-rotating two-color circularly polarized (CRTC) laser fields is investigated. A scaling law is concluded by qualitative and quantitative comparing the momentum distributions of two electrons from NSDI in CRTC laser fields for different atoms with different parameters. The scaling law indicates that the momentum distributions from an atom driven by CRTC laser frequency ω1, ω2 and laser intensity I are the same as that from another atom irradiated by CRTC laser frequency kω1, kω2 and laser intensity I×k^3. This study can provide an avenue to research of two-color laser field ionization.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Khan Muhammad   Khan Muhammad Usman   Zhao Yongpeng   Zhao Dongdi   Cui Huaiyu   Cao Ziyue   An Bo   Zhang Fefei  

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In this paper, we firstly demonstrated the influence of prepulse current and delay time on the intensity of a discharge pumped Ne-like Ar soft X-ray laser operating at 46.9nm laser with 4.8mm by employing alumina capillary having an inner diameter of 4.8mm. Specifically, the delay time was changed from 8 to 520µs in small intervals. The predischarge current was increased from 25A to 250A through small steps while keeping the main discharge current constant. Usually, a small predischarge current is applied to Ar-filled capillary to attain a plasma column having sufficient preionization before the injection of the main current. The predischarge current of 140A was declared as the best current to obtain lasing with 4.8mm diameter capillary. The laser spots were captured at best time delays for the predischarge currents of 25, 45, 80, 140 and 250A which support the experimental results. We observed that by applying the predischarge current of 140A, the laser spot exhibits small divergence, higher symmetry, and uniformity, which is clear evidence of strong amplification. The laser spot obtained at 140A is cylindrically symmetric and have well structure than those reported by all other groups in the literature. Hence, the laser spot indicates that the laser beam is highly focusable and beneficial for 46.9nm laser application. Results of this paper might open a new way to enhance applications of 46.9nm capillary discharge soft X-ray laser.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Li Gongqing   Duan Xiaofeng   Huang Yongqing   Liu kai   Ren Xiaomin  

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We proposed a method to form a flat transmitted serrated-phase high-contrast-index subwavelength grating (HCG) beam splitter (SP-HBS) for all dielectric materials which is to alternately arrange two kind of grating bars with a phase difference of π. Comparing to the typical linear-phase HCG beam splitter (LP-HBS) which consist of two symmetrical deflecting grating, the SP-HBS is extensible in size, can achieve excellent splitting abilities regardless of normal incidence or small-angle oblique incidence with large deflection angles and higher diffraction efficiency, lower energy loss and higher tolerance of fabrication accuracy. Furthermore, the incident light can be split in half at any part of the SP-HBS, and the output beams of light maintain the original shape. In this paper, we designed an SP-HBS with a 44.8° deflection angle and a 90.28% transmissivity.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Zhou Heng   Gao Chunqing   Fu Shiyao   Zhai Yanwang   Zhang Jianqiang  

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We experimentally demonstrated an approach to generate arbitrary total angular momentum (TAM) states by using two liquid crystal devices. Photons’ TAM, the sum of spin and orbital angular momentum (SAM/OAM) under paraxial ap-proximation, have found many applications in optics, and attached increasing attention in recent years. Our approach is based on the orthogonality of two eigen SAM components, that arbitrary TAM states will be produced through encoding different holograms in one system. The comparison with theoretical predications yields excellent agreement, including both separable state and non-separable state. The proposed scheme takes a step forward for generating complex structured fields, and also broaden its application to various fields like laser processing, large capacity data-transmission and so on.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Fang Yuwei   Cheng Junjie   Wang Shengbo   Gu Chun   Zou Gang   Ming Hai   Xu Lixin  

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A range-extended acidity detector based on Nile red was designed and analyzed in this work. In light of the good lasing property and solvatochromism characteristic of Nile red/ethanol solution, we have obtained laser spectra of sulfuric acid in different concentrations doped in this substrate. Moreover, to expand the acidity detection range, we proposed a tandem cuvette system containing Rhodamine 6G/ethanol and Nile red/ethanol. Consequently, the detection range could be enlarged from 26 nm to 40 nm, not only by the wavelength peak but also by the intensity ratio of dual-wavelength laser output. In addition, by changing the detection and substrate material the whole detection range could be expanded, and therefore a wide range of applications in polarity and acidity detection could be implemented via this method.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

ZENG Chunhong   Lin Wenkui   He Tao   Zhao Yukun   Sun Yuhua   Cui Qi   Zhang Xuan   Lu Shulong   Zhang Xuemin   Xu Yameng   Kong Mei   Zhang Baoshun  

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A monolithic integrated ultraviolet-infrared (UV-IR) dual-color photodetector based on graphene/GaN heterojunction was fabricated by vertically integrating GaN nanowire array on silicon substrate with monolayer graphene. The device detects ultraviolet and infrared lights by different mechanisms. The ultraviolet detection is accomplished by the forbidden band absorption of GaN, and the infrared detection is realized by the free electron absorption of graphene. At peak wavelengths of 360 nm and 1540 nm, the detector has responsibilities up to 6.93 A/W and 0.11 A/W, detection efficiencies of 1.23×10¹² cm·Hz^1/2W^-1 and 1.88×10¹⁰ cm·Hz^1/2W^-1, respectively, and a short response time of less than 3 ms.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Li Dongdong   Mo Jianye   Wang Chong   Liu Wei   Ge Haibo   Han Dongdong   Hao Aihua   Chai Baoyu   She Jianbo  

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Li ions affect the upconversion efficiency by changing the local crystal field of luminescent center. Herein, in order to improve the upconversion efficiency of NaYF4:Yb3+/Eu3+, a series of NaYF4:Yb3+/Eu3+ micro-particles with different Li+ doping concentration were synthesized by hydrothermal synthesis method respectively. Firstly, the structure and morphology of NaYF4:Yb3+/Eu3+ upconversion micro-particles (UCMPs) with different doping concentration were analysized by X-ray diffraction and scanning electron microscope (SEM). SEM results show that the UCMPs are not only highly crystallized, but also hexagons with different Li+ concentration of NaYF4:Yb3+/Eu3+. X-ray diffraction shows that the crystal field around Eu3+ changes with the increase of Li+ concentration. Then the fluorescence spectrum of NaYF4:Yb3+/Eu3+ was studied under the irradiation of 980nm laser. The results show that the fluorescence intensity of NaYF4:Yb3+/Eu3+ with 2% Li+ is the strongest, which is twice stonger the NaYF4:Yb3+/Eu3+ without Li+. Finally, the fluorescence imaging analysis of NaYF4:Yb3+/Eu3+ with 2% Li+ concentration was carried out. The upconversion micro-particles are used to screen printing to evaluate the imaging effect on different sample surfaces. The results show NaYF4: Yb3+/Eu3+ (with 2% Li+) have great application prospects in anti-counterfeiting recognition.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Feng Zhao   Yu Jianjun   Li Jingling  

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We proposed and demonstrated a new scheme for simultaneous generation independent wired and wireless signals employing an integrated polarization multiplexing modulator. In the experimental system, a 10 Gb/s wired signal is imposed on the original optical carrier with one polarization, while a wireless signal with bit rate lager than 4 Gb/s is carried on the generated millimeter wave with 76.44 GHz which has the polarization is orthogonal to the wired signal. The dual services are successfully delivered over a 15km standard single mode fiber, while the power penalties of the wired and wireless signals are around 0.4 dB and 1.5 dB, respectively.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Fan Li   Wang Xiaoyu   Zhao Xiaodong   Wang Jianhui   Shen Jun   Fan Huibo   Zhu Jun   Shen Mingya  

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A continuous-wave Nd:YVO4/BaWO4 Raman laser generating simultaneous multi-wavelength 1st-Stokes and 2nd-Stokes emissions is demonstrated for the first time. Investigations concerning different pump spot sizes and crystal lengths were conducted to improve thermal effect and pump absorption. Three 1st-Stokes lasers at 1103.6, 1175.9, 1180.7 nm and two 2nd-Stokes lasers at 1145.7, 1228.9 nm are obtained simultaneously using the Raman shifts of 925 cm-1, 332 cm-1 in BaWO4 and 890 cm-1 in YVO4. At the incident pump power of 23.1 W, 1.24 W of the maximum Raman output power is achieved, corresponding to an optical conversion efficiency of 5.4%. We also present a theoretical analysis of the competition between different Stokes lines.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Zhou Changhe  

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It is well-known that Chirped Pulse Amplification (CPA) technique is awarded by 2018 Nobel Physical Prize to Mourou and Strickland. The compression and stretch using gratings is the essence of CPA technique for amplifying femtosecond laser pulse. It seems less introduced to the public that there are also other structures for compression and stretching of femtosecond laser pulses using other diffractive gratings, such as doubled-density gratings, deep-etched gratings. Therefore, from the view of diffractive optics, CPA technique is reviewed with different approaches and experimental implementations which are not only useful for a more comprehensive retrospective overview of CPA, but also for the prospective of the CPA technique in the future.

       PDF全文        Chinese Optics Letters ，2020年第18卷第11期 pp.11      

Tong Jiang   Si Gao   ZhenNan Tian   Zhang Hanzhuang   LiGang Niu  

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A 400 nm femtosecond laser was used to ablate the surface of HPHT diamond, and the subwavelength surface microstructures with a period of 100 nm were achieved. A variety of micro-nano composite surface structures were prepared by changing the polarization direction and laser scanning direction. By dynamically adjusting the laser polarization and the laser scanning tracks, a maskless direct writing fabrication of micro-nano complex structures was realized. The micro-nano patterning on ultra-hard and super-stability diamond provides a new idea for the preparation of friction reducing surfaces, nano imprint transfer templates, SERS test substrates, and micro-nano optical structures.

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Wang Xinkun   Xiong Kedi   Jin Xin   Yang Sihua  

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The previous methods to measure flow speeds by photoacoustic microscopy solely focused on either the transverse or the axial flow component, which did not reflect absolute flow speed. Here we present absolute flow speed maps by combining Doppler bandwidth broadening with volumetric photoacoustic microscopy. Photoacoustic Doppler bandwidth broadening and photoacoustic tomographic images were applied to measure the transverse flow component and the Doppler angle, respectively. Phantom experiments quantitatively demonstrated that a range of 55º to 90º Doppler angle, and 0.5 to 10 mm/s of flow speed can be measured. This tomography-assisted method provides the foundation for further measurement in vivo.

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Chang Hongxiang   Xi Jiachao   Su RongTao   Ma Pengfei   Ma Yanxing   Zhou Pu  

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Coherent beam combining (CBC) of 60 fiber lasers by using stochastic parallel gradient descent (SPGD) algorithm has been demonstrated. The functions of pinhole(s) on the power distributions in the far-field have been systematically simulated on both in-phase and out-of-phase modes. Only one photoelectric detector was used to detect the combined power in the far-field central lobe of in-phase mode state. When the phase controller was in closed loop, the contrast of the far-field intensity pattern was as high as ~97% with residual phase error of ~λ /30, and ~34.7% of the total power was contained in the central lobe.

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Liu Chenxi   Liu Kun   Wang Xiaorun   Wu Luyan   Li Jian   Wang Qin  

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Nonlocal correlations observed from entangled quantum particles imply the existence of intrinsic randomness. Normally, local projective measurements performed on a two-qubit entangled state can only certify one-bit randomness at most. While non-projective measurement can certify more randomness with the same quantum resources. In this paper, we carry out an experimental investigation on quantum randomness certification through a symmetric, informationally complete, positive operator-valued measurement, which in principle can certify the maximum randomness through an entangled qubit. We observe the quantum nonlocal correlations that are close to the theoretical values. In the future, this work can provide a valuable reference for the research on the limit of randomness certification.

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Sun Fei   Liu Yichao   Yang Yibiao   Chen Zhihui   He Sailing  

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A novel way to design arbitrarily-shaped retro-reflectors by optic surface transformation is proposed. The entire design process consists of filling an optic-null medium between the input and output surfaces of the retro-reflector, on which the points have 180 degree reverse corresponding relations. The retro-reflector can be designed to be very thin (a planar structure) with high efficiency. The effective working angles of our retro-reflector are very large (from -80 degrees to +80 degrees), which can in principle be further extended. Layered metal plates and zero refractive index materials are designed to realize proposed retro-reflector using for a TM polarized beam.

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Chen Xi   Zhou Ciming   Fan Dian   Qian Li   Pang Yandong   Wei Cong   Zhao Chenguang   Liang Sijing   Li Yuxiao  

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We propose a novel modified frequency-shifted interferometer (MFSI) where a Mach-Zehnder interferometer (MZI) is added in order to obtain wavelength information. We use the Hilbert transform(HT) to extract the wavelength information from the phase of the interference pattern and construct the relationship between phase and wavelength. The laser wavelength measurement experiment is used to verify the compound interferometer.Experimental results demonstrated that our method could obtain the wavelength from the phase, which is of great significance for demodulation Fiber Bragg Grating( FBG) based on frequency-shifted interferometer (FSI).

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Zhang Hai   Shang Jianyu   Liu Xiujuan   Wang Feiru   Sun weimin   Liu Yongjun  

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This paper presents a new type of optical fiber probe used to detect temperature, whose structure is very simple. The optical fiber probe is filled with cholesteric liquid crystals (CLCs) whose reflected light varies with temperature. The experimental results show that the proposed sensor can achieve a temperature sensitivity of 5.64 nm/°C. The sensor has the advantages of simple structure, low cost and easy to mass manufacture. Its size is very tiny (the tapered structure, 125 μm in maximum diameter and <300 μm in length) and easy to integration and measure. Meantime, the tapered structure of the probe is also ideal for measuring small samples such as cells and microfluidic channel, which will be a promising candidate for monitoring temperature fluctuations in small spaces.

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Qu Zhiyuan   Lu Ping   Li Yujian   Fu Xin   Zhang Wanjin   Liu Deming   Zhang Jiangshan  

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In this letter, a low-frequency acoustic sensor based on extrinsic Fabry-Pérot (FP) interferometer with silicon nitride (Si3N4) membrane is demonstrated. Using micromachining techniques, the 800 nm thick Si3N4 membrane is deposited on a 8 mm×8 mm×400 μm silicon (Si) substrate. All the assembly procedures of the sensor are focused on the substrate to avoid any damage to the membrane itself, compared to general membrane transfer methods. The frequency response of the proposed sensor is discussed theoretically and experimentally demonstrated. The sensor performs an excellent flat response to the tested acoustic frequency range of 1 Hz to 250 Hz. The phase sensitivity is around -152 dB re. 1 rad/μPa with sensitivity fluctuation less than 0.8 dB. The frequency response characteristic shows a promising potential of the sensor in low frequency acoustic signal sensing applications.

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Wu Jiaqi   Zheng Yinhui   Zeng Zhinan   Li Ruxin  

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High-order harmonic generation originated from zigzag graphene nanoribbons (ZGNR) induced by intense laser pulses is investigated theoretically. During the interaction between the intense mid-infrared laser with the ZGNR, we find that localized edge states mainly contribute to the generation of the low-order harmonics, while cutoff harmonics result from the other confined states. Our result shows that the edge state effect of ZGNR with narrow width can enhance the conversion efficiency of low-order harmonics, rather than the higher harmonics extended to the cutoff region.

       PDF全文        Chinese Optics Letters ，2020年第18卷第10期 pp.10      

Chen Yung-Fu   Lee C. C.   Wang C. H.   Hsieh M. X.  

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The study of structured laser beams has been one of the most active fields of research for decades, particularly in exploring the laser beams with orbital angular momentum. The direct generation of structured beams from laser resonators is deeply associated with the formation of transverse modes. The wave representations of transverse modes of spherical cavities are usually categorized into Hermite-Gaussian (HG) and Laguerre-Gaussian (LG) modes for a long time. Enormous experimental results have revealed that the generalized representation for the transverse modes is the Hermite-Laguerre-Gaussian (HLG) modes. We make a detailed overview for the theoretical description of the HLG modes from the representation of SU(2) in the Jordan–Schwinger map. Furthermore, we overview how to derive the integral formula for the elliptical modes based on the Gaussian wave-packet state and the inverse Fourier transform. The relationship between the HLG modes and elliptical modes is linked by the quantum Fourier transform. The most striking result is that the HLG modes can be exactly derived as the superposition of the elliptical modes without involving Hermite and Laguerre polynomials. Finally, we discuss the application of the HLG modes in characterizing the propagation evolution of the vortex structures of HG beams transformed by astigmatic mode converter. This overview certainly provides not only a novel formula for transverse modes but also a pedagogical insight into quantum physics.

       PDF全文        Chinese Optics Letters ，2020年第18卷第9期 pp.09      

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      

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      

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      

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      

chen minghui   jia wenyu   he jintao   geiser martial   zheng gang  

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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.  

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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      

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

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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  

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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      

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

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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      

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      

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      

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      

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      

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      

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      

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      

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      

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 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      

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      

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      

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      

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      

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      

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      

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      

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      

Xu Yongchi   Peng Huanfa   Guo Rui   Du Huayang   Hu Guoqing   Zhu Lixin   Chen Zhangyuan  

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A wideband tunable optoelectronic oscillator (OEO) based on a tunable single-bandpass microwave photonic filter (MPF) and a recirculating delay line (RDL) is proposed and experimentally demonstrated. The MPF is formed by cascading a finite impulse response filter and an infinite impulse response filter, which can enhance the quality-factor of the MPF and suppress the side modes of the OEO. Frequency response of the tunable MPF is theoretically analyzed. By placing the MPF into OEO, tunable microwave signal from 10.3GHz to 26.7GHz and 100MHz-step tunability are experimentally demonstrated. The phase noise is -113 dBc/Hz@10kHz. The results agree well with the theory.

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

Zhang Xiaotong   Yuan Tingting   Yang Xinghua   Guan chunying   Yang Jun   Liu Zhihai   Deng Hongchang   Yuan Libo  

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In-fiber integrated optics is an attempt to use silica fiber as a substrate, integrating various optical paths or optical components into a single fiber, to build a functional optical device or component, to realize a micro optical system, achieving various functions. In-fiber integrated optics is expected to be a new branch of photonics integration. This integration technique enables conve-nient light beams control and manipulation inside in one fiber. It also provides a research platform with micro and nano scale for interaction between lightwave and microfluidic maters. In this paper, we briefly summarize the main ideas and key technologies of the in-fiber integrated optics by series integration examples.

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

Luo Binbin   Lu Huafeng   Shi Shenghui   Zhao Mingfu   Lu Jiao   Wang Yajie   Wang Xing  

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We demonstrate a fiber refractive index (RI) sensor based on excessively tilted fiber grating (ExTFG) immobilized by large-size plasmonic gold nanosells(GNSs). The GNSs are covalently linked on ExTFG surface. Experimental results demonstrate that both the intensity of transverse magnetic (TM) and transverse electric (TE) mode of ExTFG are significantly modulated by the localized surface Plasmon resonance (LSPR) of GNSs due to the wide-range absorption band. The wavelength RI sensitivities of TM and TE mode in the low RI range of 1.333~1.379 are improved by ~25% and ~14% after GNSs immobilization, respectively, and the intensity RI sensitivities are ~599%/RIU and ~486%/RIU, respectively.

       PDF全文        Chinese Optics Letters ，2018年第16卷第10期 pp.10      

Liu Jingsong   Cheng Qiyuan   Yue Daguang   Zhou Xucong   Meng Qingtian  

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In this paper, we study the molecular alignment and orientation driven by two elliptically polarized laser pulses. It is shown that the field-free molecular alignment can be achieved in a three-dimensional(3D) case while the field-free molecular orientation only along the x and y directions, and that the field-free alignment and orientation along different axes is related to the populations of the rotational states. It is demonstrated that changing the elliptic parameter is efficient for controlling both in-pulse and post-pulse molecular alignment and orientation. And the delay time also has an influence on the field-free molecular alignment and orientation.

       PDF全文        Chinese Optics Letters ，2018年第16卷第10期 pp.10      

Sun Xiaoyan   Cui Dongmei   Hu Youwang   Chu Dong kai   Chen Guowei   Yu Jinlong   Zhou Jianhang   Duan Ji'an  

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In order to improve the morphology of microchannels fabricated by femtosecond laser ablation, the thermal process was introduced into the post-treatment processing. It was found that thermal process can not only decrease the roughness but also the width and depth of the microchannel. The change rates of width, depth, and roughness of microchannel increases with processing temperature. When we prolong the time of constant temperature, the change rate of width decreases at beginning, and then it tends to be stable. However, the change rates of depth and roughness increase, and then they tend to be stable. In this paper, we discuss the reasons of the above phenomena.

       PDF全文        Chinese Optics Letters ，2018年第16卷第10期 pp.10      

Xing Jianfei   Wen Jianxiang   Wang jie   pang fufei   Chen Zhenyi   Liu Yunqi   Wang Tingyun  

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A few-mode erbium doped fiber (FM-EDF) is fabricated using MCVD in combination with liquid solution, and the core and cladding diameters of the fiber are approximately 19.44 and 124.12 μm, respectively. The refractive index difference is 0.98%, numerical aperture (NA) is 0.17, and normalized cut-off frequency V at 1550 nm is 6.81. Therefore, it is a five-mode fiber, and can be used as gain medium of higher order mode. Furthermore, a long period of fiber grating (LPFG) is fabricated, which can convert LP01 mode to LP11 mode, and its conversion efficiency is up to 99%. And the first order orbital angular momentum (OAM) is also generated by combining LPFG and polarization controller (PC). Then, an all-fiber amplification system based on FM-EDF and LPFG, for LP11 mode and first order OAM beams, is built up. Its On-Off gain of LP11 mode beam is 37.2dB at 1521.2 nm. And the variation, which transverse mode field intensity of first order OAM is increased with the increasing of pumping power, is obvious. These show that both LP11 mode and first order OAM beams are amplified in the all-fiber amplification system. This is a novel all-fiber amplification, which can be used in the optical communication fields.

       PDF全文        Chinese Optics Letters ，2018年第16卷第10期 pp.10      

Ge Xulei   Yuan Xiaohui   Yuan Fang   Wei Wenqing   Yang Su   Liu Feng   chen min   Zhao Li   Sheng Zhengming   Zhang Jie  

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The temporal profiles of high-power short-pulse lasers reflected from self-induced plasma mirrors (PM) were measured with high temporal resolution in the sub-picosecond window. The leading front shape of the laser pulse is found to depend sensitively on the laser fluence on PM surface. The spectral modulation is found to play a key role in pulse profile shaping. Our finding will extend our knowledge on properly using plasma mirror.

       PDF全文        Chinese Optics Letters ，2018年第16卷第10期 pp.10      

Zhang Li   Li Fangye   Wang Shuai   Wang Qi   Luan Kairan   Chen Xi   liu xiuhuan   Qiu Lingying   Chen Zhanguo   Zhao Ji-Hong   Hou Lixin   Gao Yanjun   jia Gang  

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In this paper, we have demonstrated significant electric field induced (EFI) optical rectification (OR) effects existing in the surface layers of germanium (Ge), and measured the distributions of EFI OR signals along the normal directions of surface layers of Ge samples. Based on the experimental results, the ratios of the two effective second-order susceptibility componentsχ_zzz^((2eff))/χ_zxx^((2eff)) for Ge(001) , Ge(110) and Ge(111) surface layers can be estimated to be about 0.92, 0.91, and 1.07, respectively. The results indicated that the EFI OR can be used for analyzing the properties on surface layers of Ge, which has potential applications in Ge photonics and optoelectronics.

       PDF全文        Chinese Optics Letters ，2018年第16卷第10期 pp.10      

zhou linjie   Wang Xinyi   Lu Liangjun   Chen Jianping  

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Optical delay lines (ODLs) are one of the key enabling components in photonic integrated circuits and systems. They are widely used in time-division multiplexing, optical signal synchronization and buffering, microwave signal processing, beam forming and steering etc. The development of integrated photonics pushes forward the miniaturization of ODLs, offering improved performances in terms of stability, tuning speed and power consumption. The integrated ODLs can be implemented using various structures, such as single or coupled resonators, gratings, photonic crystals, multi-paths switchable structures, recirculating loop structures. The delay tuning in ODLs is enabled by either changing the group refractive index of the waveguide or changing the length of the optical path. This paper reviews the recent development of integrated ODLs, with a focus on their abundant applications and flexible implementations. The challenges and potentials of each type of ODLs are pointed out.

       PDF全文        Chinese Optics Letters ，2018年第16卷第10期 pp.10      

Liu Jiao   Liu Yang   Tang Xiaojun   Wang Chao  

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We demonstrate a high-efficiency and high-power quasi-three-level laser based on a trapezoidal composite slab architecture with a 270 μm-thick Yb-doping surface. The design of surface-doped slab architecture, temperature effects, laser oscillator model and laser oscillator experiments with surface-doped slab as laser host media have been presented. By theoretical calculation, the temperature rise in the surface-doped slab is only seventh of that is in the bulk doped slab at the same maximum pump power of 30 kW. Finally, in the laser oscillator experiments, the output energy of 21.6 J is obtained when the pump energy is 48 J with the repetition rate of 5 Hz and pulse width of 1 ms. The optical-optical efficiency is 45%.

       PDF全文        Chinese Optics Letters ，2018年第16卷第10期 pp.10      

He Xi   Liu Cheng   Zhu Jianqiang  

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We propose a novel on-line beam diagnostic method based on beam splitting single-shot phase retrieval. The incident beam to be measured is diffracted into many replicas by a Dammann grating and then propagate through a weakly scattering phase plate with known structure, the exiting beams propagate along their original direction and form an array of diffraction pattern on the detector plane. By applying the intensity of diffraction patterns into an iterative algorithm and calculating between grating plane, weakly scattering plane, and the detector plane, the complex field of incident beam can be reconstructed rapidly, the feasibility of this method is verified experimentally with wavelength of 1053nm and 632.8nm.

       PDF全文        Chinese Optics Letters ，2018年第16卷第9期 pp.09      

Guo Xin   Ding Jinbin   Zhou Yi   Wang Yu  

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The ablation of Sintered Silicon Carbide Ceramics by ArF excimer laser were studied. Three zones are generated: the ablation zone presented molten morphology and composed by Si and C phase; the condensation zone formed by vaporized SiC; the oxidation zone showed the characteristics of thermal oxidation. The ablation depth and oxidation range increase linearly with fluence and pulses within 0.5-4J/cm2, but the normalized ablation efficiency is constant (3.60±0.60). The theoretical photochemical ablation depth supplies 25% of the total depth at 1J/cm2 but decreases to 16% at 4J/cm2. The ablation is dominated by photothermal effect and conforms to thermal evaporation mechanism.

       PDF全文        Chinese Optics Letters ，2018年第16卷第9期 pp.09      

Wang Kejia   Gu Xinyang   Zhang Zhenwei   Yang Zhengang   Liu Jinsong   Wang Shenglie  

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Previous research shows that few-cycle laser (FCL) pulses with low energy and without a bias field can be used to coherently detect terahertz (THz) pulses. As we know, it is very difficult to stabilize the carrier envelop phase (CEP) of FCL pulses, i.e. there are some random fluctuations for the CEP. Here we theoretically investigate the influence of such instability on the accuracy of THz detection. Our results show that although there is an optimum CEP for THz detection, the fluctuations of CEP will lead to terrible thorns on the detected THz waveform. In order to solve this problem, we propose an approach via using two few-cycle laser pulses with opposite CEPs, i.e. their CEPs are differed by <i>π</i> .

       PDF全文        Chinese Optics Letters ，2018年第16卷第9期 pp.09      

Sulaiman Abdul Hadi   Abdul kadir Muhammad Zamzuri   YUSOFF NELIDYA   Cholan Noran Azizan   Abdullah Fairuz   Abas Ahmad Fauzi   Alresheedi Mohammed Thamer   Adzir Mahdi Mohd  

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We demonstrate a broad bandwidth multiwavelength laser based on a bidirectional Lyot filter and semiconductor optical amplifier with a mechanism of intensity dependent loss as the flatness agent. A wide bandwidth of multiwavelength spectrum of 32.9 nm within 5 dB uniformity is obtained under optimized polarization parameters. For this case, the number of generated lasing lines is 329 with a fixed wavelength separation of 0.1 nm. The power stability of this multiwavelength laser is less than 1.35 dB within 200 minutes time frame. This shows that the bidirectional Lyot filter provides an alternative option for multiwavelength generation in laser systems.

       PDF全文        Chinese Optics Letters ，2018年第16卷第9期 pp.09      

zhou daibing   Zhao Lingjuan  

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We report 20 Gb/s transmission of 4-level pulse amplitude modulation (PAM) signal using a directly modulated tunable distributed Bragg reflector (DBR) laser, Transmission distance over 20 km was achieved without using optical amplifiers and optical dispersion compensation modules. A wavelength tuning range of 11.5 nm and the 3-dB bandwidth greater than 10 GHz over the entire wavelength tuning range was obtained.

       PDF全文        Chinese Optics Letters ，2018年第16卷第9期 pp.09