Zhao Mantong   Zhang Dawei   Zheng Lulu   Condliffe Otto   Kang Yi  

      摘要 + 此论文可免费阅读 (可能需要登录)

This study provides a rapid method for the quantification of mineral oil in rapeseed oil using near-infrared spectroscopy. The data were processed by direct orthogonal signal correction (DOSC), successive projections algorithm (SPA), partial least squares (PLS) and principle component regression (PCR). DOSC-SPA-PCR model was identified as optimal method, resulting in good correlation coefficients (R) of 0.998, root-mean-squared error (RMSE) of 0.005. A satisfactory accuracy with R and RMSE of prediction by DOSC-SPA-PCR model of 0.990, 0.006, was obtained. The results demonstrate that the proposed methodology is a promising method for the rapid quantitative detection of mineral oil in vegetable oil.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第4期 pp.04      

chen jiannong   Wang Baodong   Zhu Linwei   Han Jing   xu qinfeng  

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We propose a metalens for coaxial double wavelength focusing. One focusing spot is circular solid spot and another focusing spot is a doughnut-shaped spot which is circling the solid spot. The designed metalens was composed of meta-molecular nanostructured cell array. Each meta-molecular nanostructured cell was divided into four squares. Two slots with exactly the same shape but usually with rotation angle measured clockwise from positive x axis are etched into the gold film in diagonally connected two squares. Another two slots with the same shape but with the rotation angle measured counter-clockwise from positive x axis are etched into another two diagonally connected squares in the same cell. The lasers with two different wavelengths are transformed into right-handed and left-handed circularly polarized beam, respectively. The two sets of slots with different azimuthal rotation modulated the phases of incident right-handed and left-handed circularly polarized beam independently. The numerical simulation with FDTD software was carried out and the experimental verification was also implemented. Both of the experimental result and the numerical simulation agree well with the theoretical design.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第4期 pp.04      

Gao Cheng   Wang Zhifeng   Xu Yang   Melgosa Manuel   Xiao Kaida   Brill Michael   Li Changjun  

      摘要 + 此论文可免费阅读 (可能需要登录)

Most viable modern chromatic adaptation transforms (CATs), such as CAT16 and CAT02, can trace their roots both conceptually and mathematically to a simple model formulated from the hypotheses of Johannes von Kries in 1902, known as von Kries transform/model. However, while the von Kries transform satisfies the properties of symmetry and transitivity, most modern CATs do not satisfy these two important properties. In this paper, we propose a generalized von Kries transform which satisfies the symmetry and transitivity properties in addition to improving the fit to most available experimental visual datasets on corresponding colors.

       PDF全文 (下载：1)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Zhang Hengkang   Ji Encai   Zhang Bin   Chen Yi   Yao Baoquan   Liu Qiang  

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The generation of mid-infrared pulsed laser was achieved in Ho3+:YAG laser pumped gain-switched Cr2+:CdSe laser system with the shortest pulse duration of 4.15 ns. With a pump pulse duration of 50 ns and pump power of 2.7 W, the gain-switched Cr2+:CdSe laser achieved over 10 times pulse narrowing, obtaining the maximum peak power of 5.7 kW. The optical-to-optical conversion efficiency was 3.7%, which could be further improved with better crystal surface polishing quality. The laser central wavelength was measured to be 2.65 μm with a bandwidth (FWHM) of 50 nm. In addition, the optimized parameters for suppressing the pulse tail was discussed, while the long cavity and high output transmissivity contributed to obtain the single-peak pulses.

       PDF全文 (下载：4)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Huo Zhuang   Liu Exian   Liu Jianjun  

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A hollow-core fiber based on photonic quasicrystal arrays is theoretically proposed for high-quality lightwave propagation with high polarization maintaining and low nonlinearity. This fiber, called hollow-core photonic quasicrystal fiber (HC-PQF), can simultaneously realize high birefringence that reaches to 1.345×10-2, small nonlinear coefficient of 1.63×10-3 w-1·km-1 at communication wavelength 1.55μm due to the air-filled core and unique quasi-periodic fiber structure. To further demonstrate the controllability of the nonlinear coefficient and the application of sensor and polarization maintaining fiber, the nonlinearity is investigated by filling different inert gases in fiber core while the birefringence keeps high order of 10-2. In the wavelength range λ∈[1.53 μm, 1.57 μm], the dispersion is near-zero and flattened. The HC-PQF is expected for the applications in optical communication, high power pulse transmission, polarization beam splitter, etc.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Liu Ningning   Wang Mohan   Tang Zongyuan   Gao Lin   Jing Shuai   Gao Na   Xing Hongyu   Meng Xiangshen   He Zhenghong   Li Jian   Cai Minglei   Wang Xiaoyan   ye wenjiang  

      摘要 + 此论文可免费阅读 (可能需要登录)

Image sticking in liquid crystal display (LCD) is related to the residual direct current (DC) voltage (RDCV) on the cell and the dynamic response of the liquid crystal materials. According to the capacitance change of liquid crystal cell under the DC bias (DCB), the saturated residual DC voltage (SRDCV) can be obtained. And the response time can be obtained by testing the optical dynamic response of liquid crystal cell, thereby evaluating the image sticking problem. Based on this, the image sticking of vertical alignment nematic (VAN) liquid crystal display (VAN-LCD) filled with negative liquid crystal materials FFS1 with different cell thicknesses (3.8 μm, 11.5 μm) and different concentrations of γ-Fe2O3 nanoparticles (0.017wt%, 0.034wt%, 0.051wt%, 0.068wt%, 0.136wt%, 0.204wt% and 0.272wt%) were evaluated, and the effect of nano-doping was analyzed. It is found that the SRDCV and response time decrease firstly and then increase with the increase of the doping concentration of γ-Fe2O3 nanoparticles in the VAN cell. When the doping concentration is 0.034wt%, the γ-Fe2O3 nanoparticles can adsorb most of the free impurity ions in liquid crystal materials, resulting in 70% reduction in the SRDCV, 8.11% decrease in the decay time, and 15.49% reduction in the rise time. The results show that the doping of γ-Fe2O3 nanoparticles can effectively improve the image sticking of VAN-LCD, and provide useful guidance for improving the display quality.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Gu Hongan   Qin Zhipeng   Xie Guoqiang   Hai Ting   Yuan Peng   Ma Jingui   Qian Liejia  

      摘要 + 此论文可免费阅读 (可能需要登录)

We demonstrated a femtosecond mode-locked Er:ZBLAN fiber laser at 2.8 μm based on nonlinear polarization rotation technique. The laser generated an average output power of 317 mW with a repetition rate of 107 MHz and a pulse duration as short as 131 fs. To the best of our knowledge, this is the shortest pulse generated directly from mid-infrared mode-locked Er:ZBLAN fiber laser to date. Numerical simulation and experimental results confirm that reducing of gain fiber length is an effective way to shorten the mode-locked pulse duration in Er:ZBLAN fiber laser. The work takes an important step towards sub-100 fs mid-infrared pulse generation from mode-locked Er:ZBLAN fiber lasers.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Li Ping   Liu Jing   Huang Peng   Zhang Xingyu   Shi Jinhui   Yuan Libo   Guan chunying  

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We theoretically demonstrate a compact all-dielectric metasurface fiber-tip lens composed of sub-wavelength amorphous silicon on the end face of a multimode fiber. The full 2π phase control was realized by varying the widths of resonant units. The tunable focal length is achieved by using the thermal-optic effect of amorphous silicon. The focal length increases from 309 μm to 407 μm when the temperature changes by 300 K. The temperature control all-fiber integrated lens is compact and high-efficiency, and provides an excellent platform of fiber-tip lab. Meanwhile, the proposed fiber lens does not have any structural changes during dynamic tuning, which improves the durability and repeatability of the devices.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Huang Xiaodan   Lou娄 Chaogang朝刚   Zhang Hao   Yang Hua  

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The effects of the diameter of SiO₂ nanopillars, the diameter of Ag nanospheres, the arrays' period and the medium environment on the plasmonic lattice resonance (PLR) formed by Ag nanospheres on SiO₂ nanopillar arrays are systematically investigated. Larger diameter of SiO₂ nanopillars with other parameters kept constant will widen the PLR peak, redshift the PLR wavelength, and weaken the PLR intensity. Larger diameter of Ag nanospheres with other parameters kept constant will widen the PLR peak, redshift the PLR wavelength, and strengthen the PLR intensity. Larger arrays' period or larger refractive index of medium environment corresponds to larger PLR wavelength.

       PDF全文 (下载：1)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Li Guozhu   Xin Qing   Geng Xuxing   Liang Zhi   Liang shangqing   Huang guangming   Li gaoxiang   Yang Guo qing  

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DC current sensor based on optically pumped atomic magnetometer is proposed. It has high linearity in a wide operation range, since the magnetometer measures the absolute magnitude of the magnetic field produced by the current to be measured. The current sensor exhibits high accuracy with non-moment solenoid and magnetic shielding to suppress the influence from environment. The absolute error of the measured current is below 0.08 mA when the range is from 7.5 mA to 750 mA. The relative error is 5.54×10-5 at 750 mA.

       PDF全文 (下载：11)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Jiang Haoyan   Tang Yaoyi   Zeng Xiaohan   Xiao Ruiwen   Lv Peng   Wang Lei   Lu Yanqing  

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Measuring the microscopic temperature of graphene is challenging. We used cholesteric liquid crystal microcapsules (CLCMs) as temperature sensors to detect the local temperature of 3D porous graphene through quantitative visualization. Based on a CLCM (~20 μm in size), we determined the temperature variation in a small area with an accuracy of 0.1 °C. By analyzing the color changes between two CLCMs, we demonstrated the temperature changes dynamically in a region with a diameter of approximately 110 μm. Furthermore, by comparing the color evolution among the three CLCMs, we visualized the anisotropic thermal properties in the micro-zone. This convenient and low-cost temperature measurement method is expected to further improve graphene-based devices.

       PDF全文 (下载：1)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Shang Ying   Wang Chen   Ni Jiasheng   Zhao Wenan   Li Chang   Cao Bing   Huang Sheng   Wang Chang   Peng Gangding  

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We propose a new non-intrusive flow measurement method using the DFB-FL as a sensor to monitor flow in the pipe. The relationship between the wavelength of DFB-FL and the liquid flow rate in the pipeline is derived. Under the guidance of this theory, the design and test of the flow sensor is completed. The response curve is relatively flat in the frequency range of 10Hz to 500Hz, and the response of the flow sensor has high linearity. The flow from 0.6 m3/h to 25.5 m3/h is accurately measured under the energy analysis method in different frequency intervals. Minimum flow rate of 0.046 m/s is achieved. The experimental results demonstrate the feasibility of the new non-intrusive flow measurement method based on DFB-FL and has achieved accurate measurement of small flow rates.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Li Shanghua   Wang Qing   Song Rui   Hou Fangfang   gao mingwei   Gao Chunqing  

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We demonstrated a high-energy single-frequency Er:YAG laser. With 1470nm LDs as pumping source, single-frequency laser pulses with energy of 28.6 mJ, 21.6 mJ and 15.0 mJ are obtained at pulse repetition frequency (PRF) of 200 Hz, 300 Hz and 500 Hz, respectively. As far as we know, this is the highest single-frequency pulse energy with Er:YAG gain medium . With ring cavity design, pulse duration is maintained at hundreds of nanoseconds. This high energy single frequency laser with hundreds of nanoseconds pulse duration is a prospective laser source for light detection and ranging (Lidar) applications.

       PDF全文 (下载：4)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Yang Rui   Xue Zhenfa   Shi Zhiyong   Zhou Liqiang   Zhu Linwei  

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A type of scalable self-imaging capable of variable magnification or minification of periodic objects is demonstrated in the focal plane of a lens illuminated by a point source. The theory and the experimental results show that the self-imaging phenomenon can also be realized in the focal plane of a lens regardless of whether the distances satisfy the lens formula or not. The particular property of this scalable self-imaging effect is that the images in the focal plane can be controlled with different scaling factors only when the distances between the point source and the periodic object satisfy a certain condition. This discovery should open a new filed of diffraction imaging and new application opportunities in precision measurement.

       PDF全文 (下载：2)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Yang Fenghe   Sun Pengfei   Chen Ruixuan   Zhou Zhiping  

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Optical microring resonators are extensively employed in a wide range of physical studies and applications due to the resonance enhancement property. Incorporating coupling control of microring resonator is necessary in many scenarios, but modifications are essentially added to the resonator and impairs the capability of optical enhancement. Here we propose a flexible coupling structure based on adiabatic elimination that allows low-loss active coupling control without any modifications to the resonators. The self-coupling coefficient can be monotonically or non- monotonically controllable by the proposed coupler, potentially at a high speed. The characteristic of the coupler when implemented in silicon microring resonators is investigated detailedly using substantiated analytical theory and experiments. This work provides a general method in coupling control while ensuring the resonance enhancement property, making active coupling control in resonator-waveguide system feasible.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第1期 pp.01      

Wang Xinyi   Zhou Gangqiang   Jin Zhengtao   Lu Liangjun   Wu Guiling   zhou linjie   Chen Jianping  

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We report an 8-channel wavelength-mode optical pulse interleaver on a silicon photonic chip. Wavelength and mode division multiplexing techniques are combined to increase the repetition rate of the pulses without adding the complexity of a single dimension. The interleaver uses a cascaded Mach-Zehnder interferometer architecture as a wavelength-division (de)multiplexer, an asymmetric directional coupler as a mode (de)multiplexer, and various lengths of silicon waveguides as delay lines. A pulse sequence with a time interval of 125 ps is implemented with the repetition rate being eight times that of the initial one. The demonstrated wavelength-mode multiplexing approach opens a new route for the generation of high-speed optical pulses.

       PDF全文 (下载：2)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Song Jiajun   Meng Xianghao   Wang Zhaohua   Wang Xianzhi   Tian Wenlong   Zhu Jiangfeng   fang shaobo   Teng Hao   Wei Zhiyi  

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We demonstrate a harmonically pumped femtosecond OPO laser using a frequency-doubled mode-locked Yb: KGW laser at a repetition rate of 75.5 MHz as the pump laser. Based on a BIBO nonlinear crystal, the repetition rates up to 1.13 GHz is realized, which is the 15 times that of the pump laser. The signal wavelength is tunable from 700 nm to 887 nm. The maximum power of the signal is 207 mW at the central wavelength of 750 nm and the shortest pulse duration is 117 fs at 780 nm. The beam quality (M2 factor) in the horizontal and vertical direction of output beam are 1.077 and 1.141, respectively.

       PDF全文 (下载：2)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Chen Xiaotong   Jiang Yanyi   Li Bo   Yu Hongfu   jiang haifeng   Wang Tao   Yao Yuan   Ma Longsheng  

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We demonstrate two ultra-stable laser systems at 1064 nm by independently stabilizing to 10 cm-long Fabry-Perot cavities. The reference cavities are on a cubic spacer, which is rigidly mounted for both low sensitivity to environmental vibration and ability for transportation. By comparing against an independent ultra-stable laser at 578 nm via an optical frequency comb, the 1064 nm lasers are measured to have frequency instabilities of 6 E-16 at 1 s averaging time.

       PDF全文 (下载：1)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

hu zongfu   Jiang Zhiguo   wang jinfang   mei su  

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The resonator fiber optic gyro with the light time-division input and multiplexing output (TDM-RFOG) in the CW and CCW directions is proposed. The light time-division input in the CW and CCW directions can effectively suppress the backscattering induced noise. The TDM-RFOG is implemented with the 2×2 Mach-Zehnder interferometer (MZI) optical switch. The response time of fiber ring resonator is analyzed, and it is demonstrated by experiments that light time-division input in the CW and CCW directions can reduce the backscattering induced noise. The suppression effectiveness of backscattering induced noise in the TDM-RFOG is determined by the extinction ratio of optical switch, so a closed loop is designed to adjust the phase shift difference between the two arms of MZI optical switch to control the extinction ratio. The method that two arms of MZI optical switch with twin 90° polarization-axis rotated splices is proposed to make the extinction ratio along both slow and fast axes greater than -70dB

       PDF全文 (下载：8)        Chinese Optics Letters ，2020年第18卷第3期 pp.03      

Feng Shijia   dong liquan   Wu Tong   Tan Yong   Zhang Rui   Zhang Liangliang   Zhang Cunlin   Zhao Yuejin  

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To make further understanding of terahertz (THz) wave generation from liquid water, we study the THz wave emission from water lines of different diameters. The water line with a smaller diameter generates a stronger THz electric field for the diameters from 0.2mm to 0.5mm. The THz electric filed strength and polarity change with the relative position between the incident laser and water line. Moreover, the THz energy has an optimal radiation angle of about 60°. A two-dimensional dipole array model is introduced to illustrate the phenomenon. Our observations contribute to optimize the scheme of liquid THz source.

       PDF全文 (下载：17)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Du Zhengting   Wu Hui   Zhang Tianqi   Xie Zhenda   Lv Yangyang   Lv Xinjie   Xu Jinlong   Zhao Gang   Zhu Shining  

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Alloying in 2D has been a hot spot in the development of new, versatile systems of optics and electronics. Alloys have been demonstrated to be a fascinating strategy to modulate the chemical and electronic properties of 2D nanosheets. We firstly reported ultra-broadband enhanced nonlinear saturable absorption (SA) of Mo0.53W0.47Te2 alloy at 0.6, 1.0, and 2.0 µm. The nonlinear saturable absorption of Mo0.53W0.47Te2 SA was measured by the open aperture Z-scan technique. Compared to MoTe2 and WTe2 SAs, Mo0.53W0.47Te2 SA showed 5 times deeper modulation depth, 8.6% lower saturable intensity and one order larger FOM. Thus, our research provides a method of alloy to find novel materials with more outstanding properties for optics and optoelectronic applications.

       PDF全文 (下载：1)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Zhou Dongjie   Zhang Xiang   Lu Qi   Liang Qingqing   Liu Yi  

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We experimentally investigated the forward 353.8 nm radiation from plasma filaments in pure nitrogen gas pumped by intense circularly polarized 800 nm femtosecond laser pulses. This emission line corresponds to the B²Σ_u⁺(v' = 4) - X²Σ_g⁺ (v = 3) transition of the nitrogen ions. In presence of an external seeding pulse, the 353.8nm signal was amplified by 3 orders of magnitude. Thanks to the much enhanced intensity, we performed time-resolved measurement of the amplified 353.8 nm emission based on sum-frequency generation technique. It was revealed that the built-up time and the duration of this emission are both inverse proportional to the gas pressure, while the radiation peak power grows up nearly quadratically with pressure, indicating that the 353.8 nm radiation is of the nature of superradiance.

       PDF全文 (下载：1)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Zhao Xueqiang   Zhang Yunpeng   jie Huang   Hou Peipei   Zhu Ren   Sun Jianfeng   Hou Xia   Chen Weibiao  

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The influences of nutation trail accuracy, simplification of coupling model, spot position jitter and power variation of incident light on the detection error are analyzed theoretically. Under the condition of satisfying the requirements, the nutation radius is less than 1.13μm, the accuracy of nutation trail is less than 0.04μm and the detection range is [-5μm, +5μm]. The nutation frequency is 160 times spot position jitter frequency and 100 times intensity jitter frequency of incident light. The analysis is of great significance for determining nutation radius and frequency in the tracking system based on fiber nutation.

       PDF全文 (下载：3)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

邵 景珍   Liang Xu   王 玺   Pan Ning   Lin Ying   Wang Shimao   Deng Zanhong   Fang Xiaodong  

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The laser induced damage threshold of calcium fluoride single crystal was obtained by 193nm ArF excimer laser. The damage morphology of the crystal was analyzed. The results showed that the surface of calcium fluoride single crystal broke along the natural cleavage plane under ArF excimer laser irradiation, some fragments fell off, and Newton's rings were observed on the curved fragments. Laser-induced periodic stripe structures (LIPSS) appeared on the surface layer beneath the fragments peeled off. The spacing of LIPSS was measured，and the formation mechanism of LIPSS was analyzed based on the interference model.

       PDF全文 (下载：4)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Shi Pingyang   Wu Guiling   Hu Liang   Li Qi   Chen Jianping  

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We propose a radio frequency (RF) transfer technique with passive phase noise compensation over a fiber-optic ring. By adopting different frequencies and same wavelength (DFSW) transmission and double-sideband with carrier suppression (DSBCS) modulation, the impact of backscattering can be effectively suppressed. A stable RF frequency signal can be obtained frequency-mixing at an arbitrary access site along the fiber-optic ring. As the two-directional transmissions adopt the same fiber and same wavelength from the same laser, the bidirectional propagation symmetry can be maximally guaranteed. We experimentally demonstrate 2 GHz RF signal transfer along a 100 km standard single-mode fiber-optic ring.

       PDF全文 (下载：3)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Kong Qingqing   Jing Yiqiu   Shen Hua   Deng Shiwei   han zhigang   Zhu Ri Hong  

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High-power fiber-to-fiber coupling is extensively used in fiber laser applications, and its performance is determined by coupling efficiency. We demonstrate a novel method for alignment and monitoring efficiency by detecting backscattering power at the fiber end cap. The relationship between alignment error and backscattering power is determined by simulations and experiments. Through this method, a state-of-art kW-level Fiber-to-Fiber Optic Switch (FFOS) is developed (transmission efficiency >97%). It performs well for longer than 60 minutes. To the best of our knowledge, it is the first time to establish the mathematical model based on the method. Our results can provide guidance in high-power fiber-to-fiber coupling.

       PDF全文 (下载：3)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Sun Cuiting   Wang Ran   Jin Xiren   Wang Zemin   Liu Weiliang   Zhang Shuo   Ma Yiwei   Lin Jingyu   Li Yue   Geng Tao   Sun weimin   Qu Zhongquan   Yuan Libo  

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A novel phase-shifted long-period fiber grating (PS-LPFG) for simultaneous measurement of torsion and temperature is described and experimentally demonstrated. The PS-LPFG is fabricated by inserting a pre-twisted structure into the long-period fiber grating (LPFG) written in single-mode fiber (SMF). Experimental results show that the torsion sensitivities of the two dips are -0.114 nm/(rad/m) and -0.069 nm/(rad/m) in the clockwise direction, and -0.087 nm/(rad/m) and -0.048 nm/(rad/m) in the counterclockwise direction, respectively. The temperature sensitivities of the two dips are 0.057 nm/°C and 0.051 nm/°C, respectively. The two dips of the PS-LPFG exhibit different responses to torsion and temperature. Simultaneous measurement of torsion and temperature can be implemented using a sensor. The feasibility and stabilization of simultaneous torsion and temperature measurement have been confirmed, hence, this novel PS-LPFG demonstrates potential for fiber sensing and engineering applications.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Zhang Chunxiang   pang fufei   Liu Huanhuan   Yang Junfeng   Chen Lifeng   Wen Jianxiang   Wang Tingyun  

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We have demonstrated the highly efficient excitation of LP01 mode in ring-core fibers (RCFs) by tapering the spliced point between the RCF and the standard single-mode fiber (SMF) to optimize all-fiber OAM generation. The tapering technique has been investigated theoretically and experimentally. Before tapering, only 50% of light can be coupled from SMF to RCF. The modal interference spectrum with an extinction ratio (ER) of ~ 9 dB is observed, showing that higher-order modes are excited in RCF. By tapering the spliced point, 90% of light is coupled and the ER is minimized to be ~ 2 dB, indicating that the higher-order modes are effectively suppressed by tapering. Such tapered spliced point of RCF-SMF is further applied for all-fiber OAM generation. The efficiencies of OAM+1 and OAM-1 generation are found to be enhanced by approximate 11.66% and 12.41%, respectively, showing that tapered spliced point of RCF-SMF is a feasible way to optimize OAM generation.

       PDF全文 (下载：0)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Si Zhe   Shen Xiong   Zhu Jingxin   Lin Lei   Bai Lihua   Liu Jun  

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An all reflective self-referenced spectral interferometry based on transient grating effect is proposed for single-shot measuring the amplitude and phase of ultrashort pulses in a broadband spectral range. Except for a thin third-order nonlinear medium which was used to generate the TG signal, no transmitted optics were used in the proposed device, few-cycle pulses in a broad spectral range from DUV to Mid-IR can be characterized. With a homemade compact and alignment-free device, a 5.0fs pulse at 800nm corresponding to about two cycles and a 14.3fs pulse at 1800 nm corresponding to less than three cycles were successfully characterized.

       PDF全文 (下载：10)        Chinese Optics Letters ，2020年第18卷第2期 pp.02      

Zou Jieshu   Wang Fei  

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SO2 and NO2 are the most important pollution in atmosphere. An optimized Long Path Differential Optical Absorption Spectroscopy (LP-DOAS) system of high light intensity in ultraviolet (UV) wavelength is proposed and used to measure the concentration of SO2 and NO2 simultaneously. Contrast to the tradition DOAS, the system adopted Y-type optical fiber structure instead of combination of mirrors in the telescope. The UV light intensity test shows that the light intensity of UV can arrive to above 80% of the max measuring range when the light length reach 135m and the integral time of spectrograph is only 15ms.The system is proved to be efficacious through laboratory calibration. The maximum error of SO2 calibration is 4.19% and which is 5.22% for NO2. The error of SO2 and NO2 mixture calibration is within 10%. Field measurement is implemented in a wastewater treatment plant at winter. The measurement light path is 738m. The concentration of SO2 varies from 6μg/m3 (2.26ppb) to 20 μg/m3(7.52ppb), and the concentration of NO2 varies from 100μg/m3 (53.2ppb) to 200 μg/m3 (106.4ppb) approximately. The results are accordance with the data from monitoring station nearby in magnitude order and variation tendency.

       PDF全文 (下载：2)        Chinese Optics Letters ，2020年第18卷第2期 pp.02