Zhuang Wei   Zhao Yang   Wang Shaokai   Fang Zhanjun   Fang Fang   Li Tianchu  

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An ultranarrow bandwidth Faraday atomic filter is realized based on cold 87Rb atoms. The atomic filter operates at 780 nm on the 52S1/2, F=2 to 52P3/2, F’=3 transition with a bandwidth of 7.1(8) MHz, which is approaching the natural linewidth of the transition. The peak transmission achieves 2.6(3)% by the multi-pass probe method. This atomic filter based on cold atoms may find potential applications in self-stabilizing lasers in future.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Hussain Sajid   Raza Ahmad   Saeed Fawad   Parveen Abida   Sikhai Yan   Din Nasrud   Elemike Elias E.   Huang Qianqian   Subramanian Alagesan   Khan Qasim   Lei Wei  

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The optoelectronic applications based on the perovskites always face challenges due to the inherent chemical composition volatility of perovskite precursor. The efficiency of perovskite-based light-emitting diodes (Pe-LED) can be enhanced by improving the perovskite film via solvent engineering. A dual solvent post-treatment strategy was applied to the perovskite film which provides a synchronous effect of passivating surface imperfections and reduces exciton-quenching, as evidenced by improved surface morphology and photoluminance. Thus, the optimized Pe-LEDs reaches 17866 cd m-2 maximum-brightness, 45.8 cd A-1 current efficiency and 8.3% external quantum efficiency, and relatively low turn-on voltage (VT) of 2.0 V. Herein, we present a simple technique for the fabrication of stable and efficient Pe-LEDs.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zeng Li   Sun Xiaoyan   Chang Zikun   Hu Youwang   Duan Ji'an  

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A phase-shifted fiber Bragg grating (PS-FBG) based on microchannel was proposed and realized by combining point-by-point scanning method with chemical etching. The PS-FBG composes of a fiber Bragg grating (FBG) and a microchannel through the fiber core. The microchannel can introduce phase shift into FBG. What is more important is that it exposes the fiber core to external environment. The phase shift peak is sensitive to liquid refractive index, and it shows linear refractive index response wavelength and intensity sensitivity of 2.526 nm/RIU and -111 dB/RIU, respectively. Therefore, such gratings can be used as sensors or tunable filters.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Saeed Muhammad   Khan Imad   Shah Wajid Ali   Ali Akbar   Khan Qasim   Rehman Shafiq Ur  

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Structural geometry, electronic band gaps, density of states, optical and mechanical properties of double perovskites halides Cs2InBiX6 (X = F, Cl, Br, I) are investigated using density functional functional theory (DFT). These compounds possess genuine perovskite stoichiometry, evaluated using various geometry-based indices like tolerance factor, octahedral factor and formation energy. The fundamental electronic band gaps are direct and valued in the range 2.79-0.80 eV. These compounds have narrow band gaps (except Cs2InBiF6) due strong sp coupling of the cations. The valence band maximum and conduction band minimum are confirmed to be essentially of In 5s and Bi 6p character respectively. The splitting of Bi 6p bands due to strong spin-orbit coupling causes reduction in the band gaps. These compounds have large dispersion in their bands and very low carrier effective masses. The substitution of halogen atoms have great influence on the optical properties. The mechanical properties reveal that Cs2InBiX6 (X = F, Cl, Br, I) satisfy the stability criteria in cubic structure.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zou Ningmu   Zhou Tong   Ding Zhewen   Wang Feng   Zhang Yixin   Zhang Xuping  

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A simple and effective interference fading suppression method for Φ-OTDR using optimal peak-seeking is proposed. This method can reconstruct the vibration signal with high fidelity under the premise of using only ordinary single-mode sensing fiber without changing the structure of the traditional Φ-OTDR system. Based on the data after interference suppression, we applied different machine learning models to recognize the invasive events category. The promising results show potential applications of Ф-OTDR equipment and future implementation with machine learning algorithms.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zhang Meng   Chu Yuxi   Zhao Jun   Yan Dongyu   Li Yongzhi   Bi Genyu   Liu Bowen   Hu Minglie  

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On the basis of a home-made femtosecond Yb-doped fiber laser, we designed a compact and efficient third harmonic generation scheme by a simple compensation plate of β-BaB2O4 (BBO) crystal. The compensation plate is optimized through its thickness and cutting angle to reverse both spatial and temporal walk-off. By optimizing the parameters of the compensation plate and incident light intensity, a maximum output of 2.23 W with a repetition rate of 1 MHz at 345 nm is obtained, which implies a conversion efficiency of 23% from infrared to ultraviolet (UV).

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Yang Zixin   Han Lili   Yang Qi   Ren Xianghe   Zaheer Ud Din Syed   Zhang Xiaoyan   Leng Jiancai   Zhang Jiabao   zhang baitao   Yang Kejian   He Jingliang   Li Chunlong   Wang Jun  

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Two-dimensional (2D) Te nanosheets were successfully fabricated through the liquid-phase exfoliation (LPE) method. The nonlinear optical properties of 2D Te nanosheets were studied by the open-aperture Z-scan technique. Furthermore, the continuous wave mode-locked (CWML) Nd:YVO4 laser was successfully realized by using 2D Te as saturable absorber (SA) for the first time. The ultrashort pulses as short as 5.8 ps were obtained at 1064.3 nm with an output power of 851 mW. This primary investigation indicates that 2D Te SA is a promising photonic device in the fields of ultrafast solid-state lasers.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Zhang Zongjie   Li Wei   Ma Nan   Huang Xiaoyong  

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Bright Eu3+-activated double-perovskite Sr2LaTaO6 red-emitting phosphors were successfully synthesized by high-temperature solid-state method. Under near-ultraviolet excitation at 394 nm, the optimal Sr2LaTaO6:0.2Eu3+ phosphors emitted high-brightness red light around 613 nm with the CIE chromaticity coordinates (0.650, 0.349). Notably, the color purity can reach 92%. Impressively, the favorable thermal stability of the Sr2LaTaO6:0.2Eu3+ phosphors were characterized by temperature-dependent emission spectra at different temperatures from 303 to 463 K and the emission intensity at 423 K remained 73% of its value at 303 K. All the results suggested that the as-prepared Sr2LaTaO6:0.2Eu3+ phosphors can be used in near-ultraviolet-excitable white light-emitting diodes as red-emitting color converter.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Shaomin Li   Liqun Sun  

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Natural Logarithm Wavelength Modulation Spectroscopy (ln-WMS) is demonstrated in this letter. Unlike the conventional WMS-2f technique, it is a linear method even for large absorbance, which is the core advantage of ln-WMS. The treating method used in ln-WMS is to take the natural logarithm of the transmitted intensity. In order to determine the proper demodulation phase, the η-seeking algorithm is introduced, which minimizes the absolute value of the first harmonic within the non-absorbing region. Subsequently the second harmonic of the absorption signal is extracted by setting the demodulating phase as 2η. To illustrate the validity of ln-WMS, it was applied to water vapor experimentally. The result shows that even if the absorbance (base-e) is between 1.60 and 6.26, the linearity between ln-WMS-2f and volume fraction is still established. For comparison, measurement with conventional WMS-2f was also done, whose response no longer kept linearity. The η values retrieved in continuous measurements and the residuals were shown so as to evaluate the performance of the η-seeking algorithm. Time consumed by this algorithm was roughly 0.28s per measurement. As an alternative WMS strategy, ln-WMS has a wide range of potential applications, especially where the absorbance is large or varies over a wide area.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Dai Jie   Huang Lihua   Zhu Xinran   Guo Kai   ling liqing   Huang Huijie  

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This paper reports a detection method of two-dimensional (2D) enhancement and three-dimensional (3D) reconstruction for subtle traces with reflectance transformation imaging, which can effectively locate the trace area of interest and extract the normal data of this area directly. In millimeter- and micron-scale traces, during 3D construction, we presented a method of data screening, conversion, and amplification, which can successfully suppress noise, improve surface and edge quality, and enhance 3D effect and contrast. The method not only captures 2D and 3D morphologies of traces clearly but also obtains the sizes of these traces.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

Guo Bo   Guo Xin-Yu   Tang Li-Ge   Yang Wen-Lei   Chen Qiu-Mei   Ren Zhong-Yao  

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We propose and demonstrate the cascaded multi-wavelength mode-locked erbium-doped fiber laser (EDFL) based on ultra-long-period grating (ULPG) for the first time, to the best of our knowledge. Study found that, the ULPG can be used as both a mode-locker for pulse-shaping and a comb filter for multiwavelength generation simultaneously. Using the dual-function of ULPG, three-, four-, five-, six- and seven-wavelength mode-locked pulses are obtained in EDFL, seven of which are the largest number of wavelengths up to now. For the four-wavelength mode-locked pulses, its pulsewidth is about 7.8 ps. In experiment, the maximum average output power and slope efficiency of these pulses are 8.4 mW and 2.03%, respectively. Besides the conventional pulses, hybrid soliton pulses composed of four-wavelength pulse and single soliton are also observed. Finally, the effect of cavity dispersion on the multiwavelength mode-locked pulses is also discussed. Our findings indicate that apart from common sensing and filtering, the ULPG may also possess attractive nonlinear pulse-shaping property for ultrafast photonics application. © 2020 SIOM

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Dang Zhiya   Luo Yuqing   Wang Xue-Sen   Imran Muhammad   Gao Pingqi  

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The instability of lead halide perovskites in various application-related conditions is a key challenge to be resolved. We investigated the formation of metal nanoparticles during transmission electron microscopy (TEM) imaging of perovskite-related metal halide compounds. The metal nanoparticle formation on these materials originates from stimulated desorption of halogen under electron beam, and a subsequent aggregation of metal atoms. Based on shared mechanism, the TEM-based degradation test can help to evaluate the material stability against light irradiation.

       PDF全文        Chinese Optics Letters ，2021年第19卷第3期 pp.03      

ma xiang   Zheng Shuang   Liu Jia   Chen Quanan   lu qiaoyin   Guo Weihua  

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We propose a design of single-mode orbital angular momentum (OAM) beam laser with high direct-modulation bandwidth. It’s a microcylinder/microring cavity interacted with two types of second-order gratings: the complex top grating containing the real part and the imaginary part modulation and the side grating. The side grating etched on the periphery of the microcylinder/microring cavity can select a whispering gallery mode with a specific azimuthal mode number. While the complex top gratings can scatter the lasing mode with travelling-wave pattern vertically. With the cooperation of the gratings, the laser works with a single mode and emits radially polarized OAM beams. With an asymmetrical pad metal on the top of the cavity, the OAM on-chip laser can firstly be directly modulated with electrical pumping. Due to the small active volume, the laser with low threshold current is predicted to have a high direct modulation bandwidth about 29 GHz with the bias current of ten times the threshold from the simulation. The semiconductor OAM laser can be rather easily realized at different wavelengths such as the O band, C band and L band.

       PDF全文        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Deng Aihua   Zeng Zixuan   Deng Jianliao  

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We demonstrate a two-component detection of a coherent population trapping (CPT) resonance based on virtually-imaged phased array (VIPA). After passing through a VIPA, the two coupling lights with different frequencies in the CPT experiment are separated in space and detected individually. The asymmetric lineshape is observed experimentally in the CPT signal for each component and the comparison with the conventional detection is presented. The shift of the CPT resonant frequency is studied with both the two-component and one-component detections. Our scheme provides a convenient way to further study the CPT phenomenon for each frequency component.

       PDF全文        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Li Ruonan   Sun Lifei   Cai Yangjian   Ren Yingying   Liu Hongliang   Mackenzie Mark D   Kar AK  

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Optical channel waveguides with depressed cladding configurations have been produced in Nd,Gd:CaF2 laser crystals by using ultrafast laser inscription. Waveguide properties are investigated in terms of guiding behaviors and localized laser-induced lattice damages. Under optical pump of 808 nm light, continuous-wave waveguide lasing at 1.06 μm is achieved, with a single-mode operation and a minimum lasing threshold of 98.8 mW. Furthermore, the visible emissions of Nd3+ with short wavelengths ranging from 415 nm to 550 nm and long wavelengths from 550 nm to 625 nm are observed upon 808 nm laser excitation via the up-converted process. The intensity ratios of two wavelength ranges are proved to be tunable through changing the pumping polarizations.

       PDF全文        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Guo Ya   Cai Qiang   Jia Zhiwei   Xu Bingjie   Gao Zhensen   zhang qianwu   Zhang Ruonan   Adonis Bogris   Alan Shore K   Wang Yuncai   Li Pu  

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All-optical analog-to-digital conversion is a paramount issue in modern science. How to implement real-time and ultrafast quantization to optical pulses with different intensities in an all optical domain is a central problem. Here, we report a real-time demonstration of all-optical quantization scheme based on slicing the supercontinuum in a nonlinear fiber. In comparison with previous schemes through off-line analysis of the power of different optical spectral components in the supercontinuum, this, as far as we are aware, is the first demonstration of such functionality online in the time domain. Moreover, the extinction ratio among the quantized outputs can exceed 10 dB, which further confirms the feasibility of the proposed quantization scheme. The current 3-bit resolution in the proof-of-principle experiment is limited by the current experimental condition, but can be expected to be greatly enhanced through improving both the spectral width of the generated supercontinuum and the number of filtering channels used.

       PDF全文        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Zha Songqing   Chen Yujin   Li Bingxuan   Lin Yanfu   Liao Wenbin   Zou Yuqi   Huang Chenhui   Lin Zhanglang   Zhang Ge  

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End-pumped by a 976 nm diode laser, a high-repetition-rate Er:Yb:YAl3(BO3)4 microchip laser passively Q-switched by a Co2+:MgAl2O4 crystal is reported. At a quasi-continuous-wave pump power of 20 W, a 1553 nm passively Q-switched laser with repetition rate of 544 kHz, pulse duration of 8.3 ns and pulse energy of 3.9 µJ was obtained. To our knowledge, the 544 kHz is the highest reported value for the 1.5 µm passively Q-switched pulse laser. In the continuous-wave pumping experiment, the maximum repetition rate of 144 kHz with pulse duration of 8.0 ns and pulse energy of 1.7 µJ was obtained at the incident pump power of 6.3 W.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Liu Hui   Xie Boyang   Cheng Hua   Tian Jianguo   Chen Shuqi  

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Topological photonics provide a new opportunity for the examination of novel topological properties of matter in which energy band theory and ideas in topology are utilized to manipulate the propagation of photons. Since the discovery of topological insulators in condensed matter, researchers have studied similar topological effects in photonics. Topological photonics can lead to materials that support the robust unidirectional propagation of light without back reflections. This ideal transport property is unprecedented in traditional optics, and may lead to radical changes in integrated optical devices. In this review, we present the exciting developments of topological photonics and focus on several prominent milestones of topological phases in photonics, such as topological insulators, topological semimetals, and higher-order topological phases. We conclude with the prospect of novel topological effects and their applications in topological photonics.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Han Tianwen   Chen Hao   Li Wenwan   Wang Bing   Lu Peixiang  

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We investigate the Airy-Talbot effect of an Airy pulse train in time-dependent linear potentials. The parabolic trajectory of self-imaging depends on both the dispersion sign and the linear potential gradient. By imposing linear phase modulations on the pulse train, the Airy-Talbot effects accompanied with positive and negative refractions are realized. For an input composed of stationary Airy pulses, the self-imaging follows straight lines and the Airy-Talbot distance can be engineered by varying the linear potential gradient. The effect is also achieved in symmetric linear potentials. The study provides opportunities to control the self-imaging of aperiodic optical field in time dimension.

       PDF全文        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Wang Yurong   Wang Linli   Wu Chenyi   Li Zhaohui   Yang Lei   Wu Guang  

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We report a method to reduce the detection delay temperature drift for a single-photon detector based on the avalanche photodiode (SPAD). Both the SPAD and the comparator were temperature stabilized, resulting in an ultra-low temperature drift as 0.01 ps/℃. A stable time deviation as 0.15 ps @1000 s was realized, while the ambient temperature fluctuated rapidly from 24℃ to 44℃. To our knowledge, this is the first report on the ultra-stable delay SPAD detector in case of rapid increase or decrease of ambient temperature. It is helpful to improve the stability of onboard detectors for the optical laser time transfer between ground and space.

       PDF全文        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Xu Shaofu   Zou Weiwen  

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We propose an optical tensor core (OTC) architecture for neural network training. The key computational components of the OTC are the arrayed optical dot-product units (DPUs). The homodyne-detection-based DPUs can conduct the essential computational work of neural network training, i.e. matrix-matrix multiplication. The dual-layer waveguide topology is adopted to feed data into these dot-product units with ultra-low insertion loss and cross talk. Therefore, the OTC architecture allows a large-scale dot-product array and can be integrated into a photonic chip. The feasibility of the OTC and its effectiveness on neural network training is verified with numerical simulations.

       PDF全文        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Lu Yudong   Hu Dejiao   Zhang Mingsi   Li Xiangping   Cao Yaoyu   Li Jiafang   Yang Lechen  

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Plasmonic structural colors have plenty of advantages over traditional colors based on colorants. Pulsed laser provides an important method generating plasmonic structural colors with high efficiency and low cost. Here we present plasmonic color printing Al nanodisc structures through curvature-driven shape transition. We systematically study the mechanism of morphologic evolution of Al nanodisc below the thermal melting threshold. Multi-pulse induced accumulated photothermal effect and subsequent curvature-driven surface atom diffusion model is adopted to explain the controllable shape transition. The shape transition and corresponding plasmonic resonances of nanodisc can be independently and precisely modulated by controlled irradiations. This method opens new ways towards high-fidelity color prints in a highly-efficient and facile laser writing fashion.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Li Junyan   Qian Na   Hua Shiyu   Zou Weiwen  

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A microwave-chip-based coherent multi-frequency RF driver is developed for a channel-interleaved photonic analog-to-digital converter (PADC) system, which comprises a multi-class optical demultiplexer and supports a sampling speed of 40 GSa/s. The generated signals from the RF driver are adjustable in both amplitude and phase. We analyze the relationship between the characteristics of generated RF driver signals and the demultiplexing performance in theory based on the OSDR. It is the most effective parameter to evaluate the performance of the demultiplexer in a PADC system without an EADC. By precisely adjusting the amplitude and phase of signals, the OSDR is optimized. The results verify the compatibility between the RF driver and the PADC system.

       PDF全文        Chinese Optics Letters ，2021年第19卷第8期 pp.08      

Wen Qin   Cui Wenwen   Geng Yong   Zhou Heng   Qiu Kun  

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We demonstrate a novel method to control the free spectral range (FSR) of silica micro-rod resonator precisely. This method is accomplished by iteratively applying laser annealing on the already-fabricated microrod resonators. Fine and repeatable increasing of resonator FSR is demonstrated and the best resolution is smaller than 5 MHz, while the resonator Q-factor is only slightly affected by the iterative annealing procedure. Using the fabricated micro-rod resonators, single dissipative Kerr soliton microcombs are generated, and soliton repetition frequencies are tuned precisely by iterative annealing process. The demonstrated method can be used for dual-comb spectroscopy and coherent optical communications.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

MAO Jie   chao wang   xiang Hong   Yu Yong Ji  

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We demonstrate a three-nanosecond equidistant sub-pulse multi-step Q-switched Nd: YAG laser. In the time interval of 100ns-1000ns, three pulses with the same nanosecond interval and the same peak power are obtained at the pulse width of 24ns, 28ns and 36.6ns, respectively. The energy is 32.5mJ and the optical efficiency is 10.8%.The multi-step Q-switched method does not require to insert other optical elements into the traditional Q-switched laser, it is very suitable to obtain pulse group output with several nanosecond pulse intervals.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Peng Lingzhi   Hong Lihong   Chen Baoqin   He Peng   Li Zhiyuan  

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We use the nonlinear coupled-mode theory to theoretically investigate Second-harmonic generation (SHG) in subwavelength x-cut and z-cut lithium niobate (LN) thin-film waveguide and derive the analytical formula to calculate SHG efficiency in x-cut and z-cut LN thin-film waveguide explicitly. Under the scheme of optimal modal phase matching (MPM), two types of LN thin-film can achieve highly efficient frequency doubling of 1064nm laser with a comparable conversion efficiency due to very consistent modal field distribution of the fundamental wave and second harmonic wave and efficient overlap between them. Such a robust MPM for high-efficiency SHG in both subwavelength x-cut and z-cut LN thin-film waveguides are further confirmed in a broad wavelength range, which might facilitate design and application of micro-nano nonlinear optical devices based on subwavelength LN thin-film

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Yin Cheng   Kan xue fen   Guo Kun   Wang Tao   Xu Jiangmin   Han Qingbang   Wu Jian   Cao Zhuangqi  

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In modern optics, particular interest is devoted to the phase singularities which yield complicated and twisted phase structures by photons carrying optical angular momentum (OAM). In this paper, the traditional M-line method is applied to vortex beam (VB) by a symmetric metal cladding waveguide (SMCW) chip, which can host numerous oscillating guided modes via free space coupling. These ultrahigh order modes (UOMs) result in high angular resolution due to the high finesse of the resonant chip. Experiments show that the reflected pattern of a VB can be divided into a series of inner and outer rings, whilst both of them are highly distorted by the M-lines due to the UOMs’ leakage. Taking the distribution of the energy flux into account, a simple ray optics based model is proposed to simulate the reflected pattern by calculating the local incident angle over the cross-section of the beam. The theoretical simulations fit well with the experimental results and the proposed scheme may enable new applications in imaging and sensing complicated phase structures.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Sun Lin-Shan   Zhao Bo   Yuan Jia-Qi   Zhang Yan-Rong   Kang Ming   Chen Jing  

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We show that inhomogeneous waveguides of slowly varied parity-time (PT) symmetry support localized optical resonances. The resonance is closely related to the formation of exceptional points separating exact and broken PT phases. Salient features of this kind of non-Hermitian resonance, including the formation of half-vortex flux and the discrete nature, are discussed. This investigation highlights the unprecedented uniqueness of field dynamics in non-Hermitian systems with many potential adaptive applications.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Shi Yujiao   zhang zhenhui  

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We proposed a nonlinear photoacoustic (PA) technique as a new imaging contrast mechanism for tissue thermal-nonlinearity characterization. When a sine-modulated Gaussian temperature field is introduced by a laser beam, in view of the temperature dependence of the thermal diffusivity, nonlinear PA effect occurs which leads to the production of second-harmonic (SHPA) signals. By extracting the fundamental frequency photoacoustic (FFPA) and SHPA signal amplitudes of samples through lock-in technique, a parameter that only reflects nonlinear thermal diffusivity characteristics of the sample then can be obtained. The feasibility of the technique for thermal-nonlinearity characterization has been studied on phantom samples. In vitro biological tissues have been studied by this method to demonstrate its medical imaging capability, prefiguring great potential of this new method in medical imaging applications.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Long Jun   Cai Ping   Liu Chiyue   Qu Wei   Yan Hao  

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Aperture synthesis is an important approach to improve the lateral resolution of digital holography (DH) technique. The limitation of the accuracy of registration positions between sub-holograms affects the quality of the synthesized image and even causes the failure of aperture synthesis. It is a major issue in aperture synthesis of DH. Currently intensity images are utilized to find the registration positions of sub-holograms in aperture synthesis. To improve the accuracy of registration positions, we proposed a method based on similarity calculation of the phase images between the sub-hologram, instead of intensity images. Furthermore, a quantitative indicator, degree of image distortion (DID), was applied to evaluate the synthetic results. Experiments are performed and the results verify that the proposed phase-image based method is better than the state-of-the-art intensity-image based techniques in the estimation of registration positions and provides a better synthesized final 3D shape image.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Deng Lijun   Chen Qi   Bai Yang   Liu Guodong   Zeng Lvming   Ji Xuanrong  

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Photoacoustic microscopy (PAM) has quickly developed into a noninvasive biomedical imaging technique to achieve the detection, diagnosis, and monitoring. Compared with Q-switched Nd: YAG or OPO lasers, using a low cost and small size laser diode (LD) as an alternative light source, is conducive to achieve the miniaturization and integration for preclinical transformation. However, LD’s low peak output power needs the high numerical aperture objective to attain tight focus, which limits the working distance (WD) of the system in only 2-3 millimeters, resulting in not achieving the backward coaxial confocal mode. Here, we present a compact visible LD-based PAM system with a reflective objective to achieve a 22 mm long WD and a 10 µm lateral resolution. Different depth subcutaneous microvascular networks in label-free mouse ears have been successfully reappeared in vivo with a SNR up to 14 dB by a confocal alignment. It will be a promising tool to develop into a handy tool for subcutaneous blood vessel imaging.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Zhao Yi   Huang Qiuping   Cai Honglei   Lin Xiaoxia   He Hongchuan   Cheng Hao   Ma Tian   Lu Yalin  

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In this paper, we experimentally demonstrate ultrafast optical control of slow light in the THz range, by combing the electromagnetically induced transparency (EIT) metasurfaces with the cut wire made of P⁺-implanted silicon with short carrier lifetime. Employing the optical-pump terahertz-probe spectroscopy, we observed that the device transitioned from a state with a slow light effect to a state without a slow light effect in an ultra-fast time of 5 ps and recovered within 200 ps. A coupled oscillator model is utilized to explain the origin of controllability. The experimental results agree very well with the simulated and theoretical results. This EIT metasurfaces have the potential to be used as an ultrafast THz optical delay device.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Yan Ming   Wang Yinqi   Wang Xiaoyue   Peng Junsong   Huang Kun   Zeng Heping  

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In this paper, we demonstrated a series of short-living mode-locking (ML) states (each lasting a few to a hundred of s) that happened before a fiber laser reaching a steady ML state. With time-stretched dispersion Fourier transform spectroscopy, a rich diversity of transient multi-pulse dynamics were revealed spectrally and temporally. As a result, we found that the formation of the short-living ML states was related to abundant pump power and their decaying evolution dynamics were possibly governed by gain depletion and recovery. Our results revealed unexpected transient lasing behaviors of a soliton laser and thus might be useful to understand the complex dynamics of mode-locked lasers.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Li Ke   Gao Yantao   Zhang Haipeng   Du Guohao   Huang Hefei   Xu Hongjie   Xiao Tiqiao  

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Carbon fiber (CF)/pyrolytic graphite (PG) composites are promising structural materials for molten salt reactors because of their superior performance. Due to the minor density difference between CF and PG, existing methods are impractical for efficient three-dimensional characterization of CF/PG composites. Therefore, in this study, a method based on in-line phase-contrast X-ray microtomography was developed to solve the aforementioned problem. Experimental results demonstrate that the method is suitable for comprehensive characterization of CF/PG composites. The relationship between the microporous defects and fiber orientations of such composites was also elucidated. The findings can be useful for improving the manufacturing process of CF/PG composites.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Chen Jian   Chen Guoliang   Zhan Qiwen  

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A fiber-based source that can be exploited in stimulated emission depletion (STED) inspired nanolithography setup is presented. Such a source maintains the excitation beam pulse, generates ring-shaped depletion beam and automatically realizes dual-beam co-axial alignment that is critical for two beam nanolithography. The mode conversion of depletion beam is realized by using customized vortex fiber, which converts the Gaussian beam into donut-shaped azimuthally polarized beam. The pulse width and repetition frequency of the excitation beam remain unchanged and its polarization states can be controlled. According to the simulated point spread functions of each beam in the focal region, the full-width at half-maximum of the effective spot size in STED nanofabrication could decrease to less than 28.6 nm.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Xin Chenguang   Qi Jie   Zhang Rui   Jin Li   Zhou Yanru  

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Based on transversal second harmonic generation (TSHG) effect, we demonstrate a method for in-situ modal inspection of nonlinear micro/nanowaveguides. Pumping light are equally split and coupled into two ends of a single CdS nanobelt (NB). As pumping light counterpropagating along the NB, transverse second-harmonic (TSH) interference patterns are observed. The influence of multimode interaction on TSHG effect is discussed in detail. Using fast Fourier transform (FFT), TSH interference patterns are analyzed, indicating the existence of at least four modes inside the NB. Experimental beat lengths are found to be in well agreement with calculated results.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Tang Jiu   Zhang Guizhong   He Yufei   Ding Xin   Yao Jianquan  

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The spiderlike structures in the photoelectron momentum distributions (PMDs) of ionized electrons from the hydrogen atom are numerically simulated by using a semiclassical rescattering model (SRM) and solving the time-dependent Schrödinger equation (TDSE), focusing on the role of the phase of the scattering amplitude. With the SRM, we find that the spiderlike legs will shift to positions with smaller transverse momentum values with increasing the phase. The spiderlike patterns obtained by SRM and TDSE will be in good agreement upon considering this phase. In addition, the time differences in electron ionization and rescattering calculated by SRM and the saddle-point equations are either in agreement or show very similar law of variation, which further corroborates the significance of the phase of the scattering amplitude.

       PDF全文        Chinese Optics Letters ，2021年第19卷第7期 pp.07      

Lin Jiaming   Du Zihao   Yu Chuying   Ge Wenmin   Lyu Weichao   Deng Huan   ZHANG CHAO   CHEN XIAO   Zhang Zejun   Xu Jing  

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Due to the proliferation of underwater vehicles and sensors, underwater wireless optical communication (UWOC) is a key enabler for ocean exploration with a strong reliance on short-range bandwidth-intensive communications. A stable optical link is of primary importance for UWOC. A compact, low-power, and low-cost acquisition, pointing, and tracking (APT) system is proposed and experimentally demonstrated to realign the optical link within 0.04 seconds, even when the UWOC transmitter and receiver are in relative motion. The system successfully achieves rapid auto-alignment through a 4 m tap-water channel with a relatively large number of bubbles. Furthermore, the required minimum illumination value is measured to be as low as 7.1 lx, implying that the proposed APT scheme is robust to dim underwater environments. Meanwhile, mobility experiments are performed to verify the performance of the APT system. The proposed system can rapidly and automatically align moving targets in complex and unstable underwater environments, which can potentially boost the practical applications of UWOC.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Li Ying   Di Jianglei   Li Ren   Zhao Jianlin  

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We present a deep learning approach for living cells mitosis classification based on label-free quantitative phase imaging with transport of intensity equation methods. In the approach, we applied a pretrained deep convolutional neural network using transfer learning for binary classification of mitosis and non-mitosis. As a validation, we demonstrated the performances of the network trained by phase images and intensity images, respectively. The convolutional neural network trained by phase images achieved an average accuracy of 98.9% on the validation data, which outperforms the average accuracy 89.6% obtained by the network trained by intensity images. We believe that the quantitative phase microscopy in combination with deep learning enables researchers to predict mitotic status of living cells noninvasively and efficiently.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Wang Zhe   Wu Chaohua   Fang Zhiwei   Wang Min   Lin Jintian   Wu Rongbo   Zhang Jianhao   Yu Jianping   Wu Miao   Chu Wei   Lu Tao   Chen Gang   Cheng Ya  

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We demonstrate high quality (intrinsic Q factor ~2.8×10^6) racetrack microresonators fabricated on lithium niobate thin film with a free spectral range (FSR) of ~86 pm. By integrating microelectrodes alongside the two straight arms of the racetrack resonator, the resonance wavelength around 1550 nm can be red shifted by 92 pm when the electric voltage is raised from -100 V to 100 V. The microresonators of the tuning range spanning over a full FSR is fabricated using photolithography assisted chemo-mechanical etching (PLACE).

       PDF全文        Chinese Optics Letters ，2021年第19卷第6期 pp.06      

Wang Yajun   Tian Yuhang   Sun Xiaocong   Tian Long   Zheng Yaohui  

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Our previous work had proved a pump eld noise coupling in the seed eld injected optical parametric amplier (OPA) at a certain analysis frequency. Inspired by this noise coupling mechanism, the frequency dependent squeezing factor due to the excess pump noise was experimentally demonstrated. Apart from a reduced squeezing level with an increased noise, the results also proved that a broadband squeezing noise spectral is not frequency dependent on the amplitude modulated pump eld, but limited by the bandwidth of the amplitude modulator and OPA resonator, the effective measurement is carried out in the frequency range from 2-10 MHz. It provides a guidance to design a broader-bandwidth, higher-level bright squeezed light.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Li Huicong   Zhang Wentao   Huang Wenzhu   Yanliang Du  

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We develop a low frequency fiber Fabry-Perot (F-P) seismometer based on transfer function analysis. The seismometer structure and demodulation system accuracy are limitations of low frequency seismic monitoring. The transfer function of F-P seismometer is analyzed and the mass displacement spectrum (MDS) is introduced. MDS provides guidance for mechanical structure design and optical interferometer analysis to achieve low noise. The F-P seismometer prototype is built. The experiment shows that prototype has an average noise of 6.74 ng/√Hz below 50 Hz, and its noise is less than global New High Noise Model (NHNM) within 0.16-50 Hz, whose potential is considerable.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Wang Yunzheng   Wu Qing   Wang Huide   Liu Jiefeng   Zheng Zheng   zhang meng   Zhang Han  

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Efficiently tuning the output intensity of an optical device is of vital importance for the establishment of optical inter-connects and networks. Thermo-optical modulation is an easy-implementation and convenient approach and has been widely employed in photonic devices. In this paper, we proposed a novel thermo-optical modulator based on microfiber knot resonator (MKR) and graphene heater. Upon applying voltage to graphene, the resonant property of MKR could be thermally tuned with maximum phase shift of 2.1 π. Intensity modulation shows fast optical response time thanks to the high thermal con-ductivity of graphene and the thin microfiber diameter of MKR.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Ma Mingyi   Cui Liang   Li Xiaoying  

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Using the quantum interference of photon pairs in N-stage nonlinear interferometers (NLI), the contour of joint spectral function can be modified into islands pattern. We perform two series of experiments. One is that all the nonlinear fibers in pulse pumped NLI are identical; the other is that the lengths of N pieces nonlinear fibers are different. We not only demonstrate how the pattern of spectral function changes with the stage number N, but also characterize how the relative intensity of island peaks varies with N. The results, well agree with theoretical predictions in Ref. [1], reveal that the NLI with N pieces nonlinear fibers following binomial distribution can provide a better active filtering function. Our investigation shows that the active filtering effect of multi-stage NLI is a useful tool for efficiently engineering the factorable two-photon state – a desirable resource for quantum information processing.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Wang Haoyu   Zhang Zhiyu   Zhao Kun   Liu Wen   Wang Pei   Lu Yonghua  

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Phase carried by two orthogonal polarizations can be manipulated independently by controlling both geometric size and orientation of the dielectric nanopost. With this characteristic, we demonstrate a novel multifunctional metasruface, which converts part of the incident linearly polarized light into its cross-polarization and encodes phase of the two orthogonal polarizations independently. A beam splitter and a bifocal metalens were realized in a single-layer dielectric metasurface by this approach. We fabricated the bifocal metalens and demonstrated that two focal spots in orthogonal polarizations can be separated transversely or longitudinally at will. The proposed approach shows a new route to design multifunctional metasurface with various applications in holography, three-dimensional display.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Zhong Jie   Zhou Ji   Gao Shecheng   Liu Weiping  

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This paper firstly proposed 2D encryption based on Arnold transformation for implementing a secure DC-biased optical Orthogonal time-frequency multiplexing (DCO-OTFM) in optical-wireless communications (OWC). The encrypted data is transformed to the particular 2D matrix and decrypted by the only right key to get the correct information. Meanwhile, the number of keys in 2-dimension encryption is enormous, which prevent eavesdropper from exhaustive searching secret keys rapidly to find out the right decryption. Numerical results demonstrate that the secure DCO-OTFM based on 2-dimension encryption can effectively prevent signal decryption from the eavesdropper, which has good secure performance for applying in OWC.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Zhang Xingyu   Guan chunying   Wang Keda   Cheng Lin   Yang Jing   Shi Jinhui   Liu Hongchao   Liu Zhihai   Yuan Libo  

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A multifocal optical fiber lens is numerically demonstrated based on an all-dielectric metasurface structure. The metasurface consists of an array of rectangular silicon resonators with varying widths in order to obtain the required phase distribution. The core diameter of the multimode fiber is large enough to contain sufficient resonance units. The spatial distribution of the dielectric resonators is dictated by spatial multiplexing, including interleaving meta-atoms and lens aperture division, to achieve multi-focus properties. The proposed optical fiber metalens can produce two or three focal points along the longitudinal direction with high focusing efficiency. The size of every focal point is close to the diffraction limit and the relative intensity on each focus can be controlled by adjusting the number of the respective resonators. The proposed optical fiber lens will have a great potential in the fields of integrated optics and multifunctional micro/nano devices.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Li Xun   Li Ming   Liu Hongjun  

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An effective and simple method is proposed for fabricating the micro/nano hybrid structures on metal surfaces by adjusting femtosecond laser fluence, scanning interval and polarization. The evolution of surface morphology with the micro/nano structures was discussed in details. Also, the mechanism of light absorption by the micro/nano hybrid structures is revealed. Compared with the typical periodic light-absorbing structures, this type of micro/nano hybrid structures has ultra-low average reflectivity of 2% in the 250-2300nm spectral band and the minimum 1.5% reflectivity in UV band. By employing this method, large area of the micro/nano hybrid structures in high consistency could be achieved.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Li Kanglin   Du Jiangbing   Shen Weihong   Liu Jiacheng   He Zuyuan  

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We report a low fabrication-complexity and wideband fiber lens, which is formed by fiber facet etching and filled high refractive index UV-adhesive. The optical field can be significantly shrunk by the facet lens, so as to obtain improved optical coupling. Numerical simulations were carried out for different coupling conditions, on both fundamental mode and high order mode, for a nine-mode fiber. The fundamental mode area can be reduced from 152.17 to 12.57 μm2, and the coupling loss between the fiber lens and a photonic waveguide can be reduced to -2.9 dB with over 1000-nm 3-dB bandwidth.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Liang Chunhao   Monfared Yashar   Liu Xin   Qi Baoxin   Wang Fei   Korotkova Olga   Cai Yangjian  

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We suggest tailoring of the illumination’s complex degree of coherence for imaging of specific two- and three-point objects with resolution far exceeding the Rayleigh limit. We first derive a formula for the image intensity via the pseudo-mode decomposition and the fast Fourier transform valid for any partially coherent illumination (Schell-like, non-uniformly correlated, twisted) and then show how it can be used for numerical image manipulations. Further, for Schell-model sources, we show the improvement of the two- and three-point resolution to 0.2dR and 0.4dR, respectively, dR being the classic Rayleigh distance.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Li Shangqing   Ma Jinglong   Wu Xiaojun   Zhang Baolong   Ouyang Chen   Wang Tianze   Wang Dan   Wang Xuan   Li Yutong  

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We propose a spatial diffraction diagnostic method via inserting a millimeter-gap double slit into the collimated terahertz beam to monitor the minute variation of the terahertz beam in strong-field terahertz sources, which is difficult to be resolved in conventional terahertz imaging systems. To verify the method, we intentionally fabricate tiny variations of the terahertz beam through tuning the iris for the infrared pumping beam before the tilted-pulse-front pumping (TPFP) setups. The phenomena can be well explained by the theory based on tilted pulse front technique and terahertz diffraction.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Hou A-hui   Yihua Hu   Nanxiang Zhao   Fang Jiajie   Xu Shilong   Zhou Quan  

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The first photon bias of photon detection results in distortion of the photon waveform, which seriously affected the accurate acquisition of target information. A rapid universal recursive correction method is proposed, which is suitable for multi-trigger and single-trigger modes of photon detection. The calculation time is 2 to 3 orders of magnitude faster than Xu's method. In the experiment, we have obtained good correction results for area targets and the targets with varying depth. When the average number of echo photons is 0.89, the correlation distance of the correction waveform is reduced by 85%.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

Liu Kexuan   He Zehao   Cao Liangcai  

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The bidirectional error diffusion (BERD) algorithm is free from random phase modulation that introduces speckle noise on the reconstructed images, compared with other computer-generated phase-only hologram (POH) approaches. During the POH generation process, the amplitudes of all pixels are traditionally set to one for diffusing the errors to their neighborhood unprocessed pixels. In this paper, we reveal that the reconstruction quality depends on the uniform amplitude value for different object pattern. The pattern-adaptive bidirectional error diffusion (PA-BERD) algorithm is proposed for high-quality holographic reconstruction. The optimized amplitude value can be acquired for each object pattern and each propagation distance. The PA-BERD based POHs have shown higher reconstruction quality than traditional BERD based POHs in simulations as well as optical experiments.

       PDF全文        Chinese Optics Letters ，2021年第19卷第5期 pp.05      

jiang zengshun   An Xingqi   Zhang Yuqin   Liu Xuan   Qin Xifeng   Zhao Yanjie   Wang Huilin   Liu Guiyuan   song hongsheng  

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After the 3D self-affine fractal random surface simulated, we use the optical scattering theory to calculate the deep Fresnel region speckle (DFRS) under considering the more strict shadowing effect. The evolution of DFRS with the scattering distance and the intensity probability distribution were studied. It is found that the morphology of the scatterer has an antisymmetric relationship with the intensity distribution of DFRS, and the effect of micro-lenses on the scattering surface causes the intensity probability distribution of DFRS to deviate from the Gaussian speckle in the high light intensity area.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Zhao Yuqing   Wang Qiangguo   Meng Lihua   Yao Yongping   Liu Shande   Cui Na   su liangbi   Zheng Lihe   Zhang Huiyun   Zhang Yuping  

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The anisotropy of thermal property in Yb,Nd:Sc₂SiO₅ crystal are investigated from the temperature of 293 to 573 K. Based on the systematical study of thermal expansion, thermal diffusivity and specific heat, the thermal conductivity in Yb,Nd:Sc₂SiO₅ crystal orientated at (100), (010), (001) and (406) is calculated to be 3.46, 2.60, 3.35 and 3.68 W/(m·K), respectively. The laser output anisotropy of continuous-wave (CW) and tunable laser are characterized, accordingly. A maximum output power of 6.09 W is achieved in Yb,Nd:Sc₂SiO₅ crystal with (010) direction, corresponding to a slope efficiency of 48.56 %. The tuning wavelength ranges in Yb,Nd:Sc₂SiO₅ crystal orientated at (100), (010) and (001) is 68, 67 and 65 nm, separately. The effects of thermal properties on CW laser performance are discussed.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Qiu Feng   Han Yu  

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Electro-optic (EO) ring resonator modulators have a number of telecommunications and scientific applications, including analog optical links, optical signal processing, and frequency comb generation. Among the EO materials used to fabricate ring modulators, EO polymer has many promising characteristics, including a high EO coefficient of 100-200 pm/V (3-7 times larger than that of LiNbO3), an ultrafast EO response time (<10 fs), a low dielectric constant (3 to 4) with very little dispersion up to at least 250 GHz and a straightforward spin-coating fabrication process. These inherent characteristics will be able to combine excellent EO properties with simple processing to achieve exceptional performance in a variety of high-speed optical modulation and sensing devices. This review focuses on the research and recent development of the ring resonator modulators based on EO polymer. The first part describes the operation principle of EO ring resonator modulators, such as modulation mechanism, EO tunability and 3-dB bandwidth. Subsequently, the emphasis is placed on the discussion of the ring modulators with EO polymer as the waveguide core and the improvement of EO modulation by using EO polymer / titanium dioxide hybrid core. At the end, a series of EO polymer on silicon platforms including slot modulators, etching-free modulators and athermal modulators are reviewed.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Shi Qiangshi   Shi Qiangshi   Jin Xia   Wu Qiannan   Huang Cheng   Sun Baoyin   Gao Lei   Xu Yadong   Fu Yangyang  

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In this work, inspired by advances in twisted two dimensional materials, we design and study a new type of optical bi-layer metasurface system, each based on subwavelength metal slit arrays with phase gradient modulation, referred as metagratings (MG). It is shown that due to the found reversed diffraction law, the interlayer interaction that can be simply adjusted by the gap size, can produce a transition from optical beam splitting to high-efficiency asymmetric transmission of incident light from two opposite directions. Our results provide new physics and some advantages for designing subwavelength optical devices to realize efficient wavefront manipulation and one-way propagation.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Cao Jiayuan   Li Na   Bai Ya   Liu Peng   Li Ruxin  

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We present a velocity-gauge model for the generation of even-order high harmonics, and reveal that the even-order harmonics originate from the multiple-step transitions among the energy bands in momentum space, while the odd-order harmonics mainly from the direct transitions. The lower valence band is found vital for the generation of even harmonics. Relative intensity of even-order harmonics versus the odd orders is calculated and shows a growing trend as the laser field amplitude increases.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Li Siqiao   Zhang Tiantian   Qiao Yaojun   Zhou Ji  

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This paper proposed a hybrid layered asymmetrically clipped optical single-carrier frequency-division multiplexing (HLACO-SCFDM) scheme for dimmable visible light communication. It designs a signal structure that combines LACO-SCFDM and negative LACO-SCFDM in proportion for improving the inherent weaknesses of orthogonal frequency division multiplexing (OFDM)-based dimmable schemes and further enhancing the system performance. Compared to HLACO-OFDM-based dimming scheme, it obtains lower bit error ratio and enables efficient communication over broader dimming range. Its spectral efficiency realizes 2.875 bit/s/Hz within the dimming range of 30%-70%, and the attainable average spectral efficiency gains exceed at least 19.21% compared to other traditional dimmable schemes.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Meng Fangyuan   Yu Hongyan   Zhou Xuliang   Li Yajie   Wang Mengqi   Yang Wenyu   Chen Weixi   Zhang Yejin   Pan Jiaoqing  

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Gas sensing for measurement of gas component, concentrations and other parameters plays an important role in many fields. In this letter, a micro-ring resonator laser used for gas sensing is experimentally demonstrated. The multi-quantum-wells micro-ring laser based on whispering-gallery modes (WGMs) with an annular resonator and an output waveguide was fabricated. A single-mode laser with a wavelength of 1746.4 nm was fabricated for the first time experimentally. The output power of 1.65 mW under 40 mA injection current was obtained with a side-mode suppression ratio (SMSR) over 33 dB.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Pan Long   Deng Chenjin   yu cuiping   yue shuai   Gong Wenlin   Han Shensheng  

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The influence of the sparsity of random speckle illumination on traditional ghost imaging (GI) and ghost imaging via sparse constrains (GISC) in noise environment is investigated. The experiments demonstrate that both GI and GISC obtain their best imaging quality when the sparsity of random speckle illumination is 0.5, which is also explained by some parameters such as detection signal to noise ratio and mutual coherence of measurement matrix.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Wang Senyu   Ma Yiwei   Xiaoyang Li   Yi Yang   Sun Cuiting   Lin Jingyu   Chengguo Tong   Li Yuxiang   Geng Tao   Sun weimin   Yuan Libo  

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In this Letter, we propose and investigate a compact optical fiber sensor which aims to measure the torsion in both amount and direction with high sensitivity. This sensor is configured by a triangular-prism-shaped long-period fiber grating which is fabricated by the high frequency CO2 laser polished method. The unique design of the triangular shaped structure breaks the rotational symmetry of the optical fiber and provides the high sensitivity for torsion measurement. In preliminary experiments, the torsion response of the sensor achieves a good stability and linearity. The torsion sensitivity is 0.54 nm/(rad/m), which renders the proposed structure a high sensitive torsion sensor.

       PDF全文        Chinese Optics Letters ，2021年第19卷第4期 pp.04      

Deng Ming   Ren Tangxuan   Wang Jian   Chen Lin  

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Retroreflector that reflects light along its incident direction has found numerous applications in photonics, but the available metasurface schemes suffer from the issue of narrow bandwidth and/or a single angle of incidence. Here a retroreflector using double layers of achromatic gradient metasurfaces is reported, which can realize retroreflection over a continuous range of incidence angles within a wide spectral band. The first metasurface serves as a transmissive achromatic lens that performs a broadband spatial Fourier transform and its inverse, while the second metasurface works as a reflective achromatic lens that undergoes a wavelength- and position-dependent phase dispersions. Using this design strategy, a near-infrared retroreflector comprised of silicon nanopillars with the cross-sections of square pillars and square holes is numerically demonstrated, providing a high-performance retroreflection for polarization-independent incident light waves over a continuous range of incidence angles from 0 to 16° within an extremely broad wavelength range between 1.35 and 1.95 μm. The scheme herein can offer a design strategy of broadband retroreflectors, and impact numerous photonics applications.

       PDF全文        Chinese Optics Letters ，2021年第19卷第2期 pp.02      

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