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    Research Advances of Random Fiber Lasers and Its Applications(Invited Review)
    RAO Yun-jiang
    Acta Photonica Sinica    2019, 48 (11): 1148002-1148002.   DOI: 10.3788/gzxb20194811.1148002
    Abstract899)      PDF (9893KB)(210)       Save

    Random fiber laser is a new type of fiber lasers. Compared with conventional fiber lasers, benefiting from its modeless, better stability, higher realibility, simpler structure and many other advantages, random fiber lasers have developed quite well in recent years in realization of a number of novel light sources including high power/high efficiency, broadband, low coherence, etc, leading to many research achievements. The author of this review is the leader of the first group to carry out research on Random fiber lasers in China. The development history of random fiber lasers is firstly summarized systematically. Then, the recent advances in random fiber lasers and their applications to optical fiber sensing and communication are introduced mainly. Finally, the future developments of random fiber lasers are prospected.

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    Sapphire Fiber and Its Application in High Temperature Sensors(Invited Review)
    PANG Fu-fei, WANG Zhi-feng, LIU Huan-huan, MA Zhang-wei, CHEN Zhen-yi, WANG Ting-yun
    Acta Photonica Sinica    2019, 48 (11): 1148004-1148004.   DOI: 10.3788/gzxb20194811.1148004
    Abstract694)      PDF (3332KB)(220)       Save

    Single-crystal sapphire fibers have attracted much attention in high temperature and high pressure environments due to their high melting point, good mechanical properties and stable chemical properties. The preparation method, basic characteristics and high-temperature transmission characteristics of the single-crystal sapphire fiber are introduced. Then, the Fabry-Perot interferometer, Bragg grating and Michelson interferometer based on single-crystal sapphire fiber are discussed. The working principle and implementation methods of these sensors are analyzed. At last, in view of the difficulty of compatibility between single-crystal sapphire fiber and traditional single-mode fiber, the preparation of sapphire-derived fiber and its recent development are introduced. The future development direction of sapphire fiber is also discussed.

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    Generation of High Repetition Rate Broadband Flat Coherent Optical Frequency Comb Based on Tantalum Pentoxide Integrated Nonlinear Optical Waveguide
    WU Chun-jiang, FENG Su-chun
    Acta Photonica Sinica    2019, 48 (10): 1048003-1048003.   DOI: 10.3788/gzxb20194810.1048003
    Abstract613)      PDF (6293KB)(271)       Save

    Through the waveguide structure design and dispersion engineering, based on the soliton pulse compression, self-phase modulation, and optical wave breaking, a 0.22 m anomalous dispersion tantalum pentoxide waveguide cascaded with a 0.9 m normal dispersion tantalum pentoxide waveguide was used to produce a flat optical frequency comb with a 4 dB flatness and 60 nm bandwidth in the 1 520 nm to 1 580 nm. The spectrogram evolution during the pulse transmission process was analyzed through the X-Frog technique, and the coherence of the optical frequency comb were also studied. The analysis indicates that the self-phase modulation and optical wave breaking effects make the comb spectrum envelop broadened and flattened. The first-order mutual coherence function calculation indicates that the optical frequency comb has good spectral coherence. The simulation results show that the tantalum pentoxide integrated nonlinear optical waveguide has a good prospect in the generation of high repetition rate flat coherent broadband optical frequency comb.

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    Low-light Image Enhancement Method Using Retinex Method Based on YCbCr Color Space
    TIAN Hui-juan, CAI Min-peng, GUAN Tao, HU Yang
    Acta Photonica Sinica    2020, 49 (2): 210002-0210002.   DOI: 10.3788/gzxb20204902.0210002
    Abstract495)      PDF (11452KB)(107)       Save
    Aiming at the problem of illumination image estimation in low-light image enhancement algorithm of the Retinex model, a low-light image enhancement method based on YCbCr color space is proposed. The original low-light image is transformed from RGB (Red Green Blue) color space to YCbCr color space. The Y component in YCbCr color space is extracted and the initial illumination map L1(x,y) is constructed. The enhanced illumination image L2(x,y) is obtained by the gamma transformation of L1(x,y), the enhanced image R(x,y) is obtained according to the Retinex model, and we use a multi-scale approach to boost the details of the image R(x,y) and obtain the final enhanced image Re(x,y).The experimental results show that, the method can not only effectively improve the brightness of the low-light images, enhance the details of the image, obtain a better visual effect with fewer color and lightness distortions, but also has a faster running speed.
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    Research Progress on S Fiber Taper(Invited Review)
    YU Yong-sen, ZHU Yong-qin, ZHAO Yang, PAN Xue-peng
    Acta Photonica Sinica    2019, 48 (11): 1148009-1148009.   DOI: 10.3788/gzxb20194811.1148009
    Abstract463)      PDF (8372KB)(78)       Save

    With the development of new micromachining processes, the traditional tapered fiber has derived thousands of different microstructured fibers. Among them, S-type fiber taper has been rapidly developed due to its small size, light weight, anti-electromagnetic interference and flexibility to be directly embedded in the structured system. With the intensive study on S-type fiber tapers, fiber optic sensors based on various structures and functions of S-taper have been continuously proposed for measuring temperature, strain, refractive index, humidity and magnetic field, etc., which enriches the types of fiber optic sensors and has deepened people's understanding of the sensing mechanism. This paper comprehensively reviews the research progress of S-type fiber tapers, including sensing principle, preparation method, various sensing structure combinations and sensing applications, and prospects for its development.

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    Propagation of Nonlocal Vector Solitons under Gauss Barrier or Trap
    WENG Yuan-hang, WANG Hong, CHEN Pei-jun
    Acta Photonica Sinica    2019, 48 (10): 1048001-1048001.   DOI: 10.3788/gzxb20194810.1048001
    Abstract460)      PDF (3711KB)(233)       Save

    The propagation of vector solitons in nonlocal nonlinear media with a Gauss barrier or a Gauss trap is described by the coupled nonlocal nonlinear Schrodinger equations with Gauss-type linear potential. These equations are numerically calculated by the square operator method, and the propagation of vector solitons is simulated by the step-step method. In nonlocal nonlinear bulk media, the components of out-of-phase vector solitons are always separated spontaneously, and the repulsion between them can be suppressed by a Gauss barrier. The components of in-phase vector solitons are always fused spontaneously, and the attraction between them can be suppressed by a Gauss trap. By quantitatively analyzing the relationship between the barrier heigh/depth or width and the distance between two components of vector solitons at the normalized transmission distance of 500, it is found that if the heigh/depth and width of barrier/trap are too large or too small, Gauss linear potential can not suppress this process, or even worsen it. For out-of-phase solitons, the Gauss barrier that can effectively suppress the separation should be set to 1.10 in height and 1.00 in width. For in-phase solitons, the Gauss potential well that can effectively suppress the fusion should be set to -1.50 in depth and 1.00 in width. Results in this paper may benefit the future researches about all-optical switch, optical logic-gate, optical computing and other optical control technologies.

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    Urban Rail Train Positioning and Speed Measuring Method Based on Grating Array
    ZHU Dong-fei, WANG Yong-jiao, YANG Ye, WEN Wei, XIN Li-ping, WANG Hong-hai
    Acta Photonica Sinica    2019, 48 (11): 1148014-1148014.   DOI: 10.3788/gzxb20194811.1148014
    Abstract437)      PDF (4785KB)(131)       Save

    A train positioning and speed measuring method based on grating array was proposed to solve the monitoring problems of railway and urban rail transit, such as variable operating environment, long monitoring distance and vulnerable to lightning. The ultra-weak grating array with strong anti-electromagnetic interference ability and large multiplexing capacity is used to form vibration sensing network, and the unbalanced Mach-Zehnder interference demodulation method is used to realize the detection of train traveling vibration signal. The accurate positioning of the train is realized by the endpoint detection method based on the short-term energy after the wavelet denoising, and the running speed of the train in the area is calculated by the distance between the adjacent measuring areas and the arrival time difference of the train. An experimental system was set up between Hugong and Yezhihu stations of Wuhan Metro Line 7 for field test to verify the feasibility of this scheme. The experimental results show that this scheme can achieve accurate positioning of the real-time position of the train, with the measuring speed error is ±2 km/h. And after a long time of testing, the system based on this scheme has good reliability and stability.

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    Stable Object Tracking Method for Complex Infrared Ground Environment
    Lü Jian, DENG Bo, QUE Long-cheng
    Acta Photonica Sinica    2019, 48 (10): 1010001-1010001.   DOI: 10.3788/gzxb20194810.1010001
    Abstract432)      PDF (6585KB)(132)       Save

    Aiming at the problem of tracking failure and less robustness caused by background clutter, occlusion and object deformation in infrared object tracking, an infrared object tracking method combining tracking-learning-detection method and correlation filtering theory was proposed. Based on the traditional correlation filtering framework, the proposed method combines the direction gradient histogram feature and the luminance histogram feature to improve the model drift caused by slight deformation of the target. Aiming at the multi-peak response problem caused by background clutter and occlusion, the response of the target background area was punished, and the multi-modal detection mechanism of target and background response was established to achieve the target from coarse to fine positioning, and the adaptive learning rate was used to optimize the drift problem of the tracking model; Aiming at the problem that the object was severely occluded or the object was out of view, the global re-detection of the target was implemented to achieve the target re-capture. The experimental results show that the proposed algorithm effectively solves the object loss caused by background clutter and occlusion in the complex infrared ground environment. Based on the benchmark OTB-2015 and infrared video sequence test, compared with the mainstream correlation filtering tracking algorithms, the proposed algorithm improves the tracking accuracy and success rate by 5.6% and 4.1% respectively compared with the Long-term Correlation Tracking (LCT) algorithm; In the occlusion index test, the proposed algorithm improves the tracking accuracy and success rate by 4.6% and 6.1% respectively compared with the LCT algorithm.

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    Research Progress in Development of Glass Scintillator(Invited Review)
    Lü Shi-chao, ZHOU Shi-feng, TANG Jun-zhou, LIU Pei
    Acta Photonica Sinica    2019, 48 (11): 1148011-1148011.   DOI: 10.3788/gzxb20194811.1148011
    Abstract431)      PDF (4469KB)(265)       Save

    As a typical material for radiation detection, glass scintillator plays an important role in various applications, including medical imaging, high-energy physics, environmental monitoring and security inspection. According to structure features and applications, glass scintillator is mainly classified into high-density glass scintillator, low-density glass scintillator and glass-ceramics scintillator. This article describes various types of glass scintillators, focusing on their fabrication procedures, microstructures, optical properties and applications. The outlook of the future developments of the glass scintillators is also discussed.

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    Propagation Properties of Airy-Gaussian Beams in a Biased Photovoltaic-photorefractive Crystal
    ZHANG Tuo, CHEN Wei-jun, MU Yi-ning, LIU Chun-yang, PENG Jun-qi
    Acta Photonica Sinica    2019, 48 (10): 1048004-1048004.   DOI: 10.3788/gzxb20194810.1048004
    Abstract426)      PDF (3916KB)(175)       Save

    Propagation properties of Airy-Gaussian beams in a biased photovoltaic-photorefractive crystal are numerically investigated by using split-step Fourier method. The results show that breathing solitons that propagate stablely along a straight line can be generated when the initial amplitude of the input Airy-Gaussian beams and the external bias field of the crystal are in certain ranges. The peak intensity and the breathing period of the soliton can be controlled by adjusting the initial amplitude and the external bias field. With the increase of the initial light field distribution factor, the mean peak intensity of the soliton firstly increases and then decreases, whereas the breathing period firstly decreases and then increases. With the increase of the beam decay coefficient, the mean peak intensity of the soliton firstly increases, then decreases, and increases again. In addition, the propagation direction of the soliton can tilt to the left with a negative launch angle and to the right with a positive launch angle. The launch angle only affects the output position of the soliton and has no influence on the intensity, width and breathing period of the soliton.

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    Angular Momentum Detector Based on Surface Plasmons
    QIU Peng, HU Zheng-da, KONG Yan, JIANG Zhi-long, LIU Cheng, WANG Shou-yu
    Acta Photonica Sinica    2019, 48 (10): 1004003-1004003.   DOI: 10.3788/gzxb20194810.1004003
    Abstract413)      PDF (4053KB)(216)       Save

    In order to accurately detect the angular momentum of light, an angular momentum detector based on surface plasmons was designed. The detector is small and simple, which can detect the incident light only by etching the designed nanoslit array on a gold film. When incident light illuminates the detector, the polarization of incident light can be distinguished according to the coupling direction of surface plasmons. Moreover, by measuring the light intensity of the outgoing port compared with the total intensity of the coupling direction port, the accurate topological charge of orbital angular momentum between -1 and +1 can be quantitatively calculated. The nano-structure detector can accurately identify the angular momentum of incident light, providing a new idea for the design and development of on-chip optical system.

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    L1-2 Spectral-spatial Total Variation Regularized Hyperspectral Image Denoising
    ZENG Hai-jin, JIANG Jia-wei, ZHAO Jia-jia, WANG Yi-zhuo, XIE Xiao-zhen
    Acta Photonica Sinica    2019, 48 (10): 1010002-1010002.   DOI: 10.3788/gzxb20194810.1010002
    Abstract411)      PDF (9097KB)(196)       Save

    A model for Hyperspectral Image (HSI) restoration was proposed, which combines the L1 norm minimization of local patches and L1-2 Spatial-Spectral Total Variation (L1-2 SSTV) of global image. Firstly, the HSI was divided into local overlapping 3D patches, to reduce information loss caused by minimization of nuclear norm while improving local low-rank property. Secondly, the L1-2 SSTV regularization term with stronger sparse expression ability was proposed, to explore both spectral and spatial sparse prior simultaneously. Finally, the advantages of both worlds are combined, and a new HSI restoration model is proposed. The local norm is used to penalize spectrum low-rank term, and the L1-2 SSTV is used globally to constrain the spatial and spectral sparsity term of HSI, The model can not only effectively remove Gaussian noise, impulse noise, deadline and its mixture noise, but also reduce the dependence on the noise independent and identical distribution hypothesis, and can partially suppress the structure-related noise. Through a large number of experiments of simulated and real HSIs, and compared with the classical low-rank and total-variation-based restoration methods, experimental results were conducted to illustrate the advantage of the proposed method in HSI restoring, from visual/quantitative evaluations.

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    Mineral Element Abundance Identification Based on LIBS Emission Line Selection by Loading Space Distance of Principal Component Analysis
    GUO Kai-chen, WU Zhong-chen, ZHU Xiang-ping, LING Zong-cheng, ZHANG Jiang, LI Yun, QIAN Mao-cheng
    Acta Photonica Sinica    2019, 48 (10): 1030002-1030002.   DOI: 10.3788/gzxb20194810.1030002
    Abstract407)      PDF (3322KB)(186)       Save

    The concentration and laser-induced breakdown spectroscopy data of 64 pre-flight calibration samples, published by the ChemCam team, were used as objects of research. Principal component analysis loading space distance method was used to analyze the target element, the most sensitive laser-induced breakdown spectral line of the target element was selected, and the mineral element species and abundance were identified with the identification accuracy up to 92.8% based on this method. The result shows that principal component analysis loading space distance can be used as a criterion to obtain the critical element information of minerals element abundance before, if aim to serve for, quantitative analysis. This study reduces the difficulty in rock/mineral classification and is beneficial to unknown minerals analysis, which offers an effective identification strategy for the Martian surface rock type analysis.

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    Parameter Design and Performance Analysis of Bistatic Helium Lidar System
    PAN Ting-yu, SUN Dong-song, ZHAO Ruo-can, LAN Jia-xin, HAN Yu-li, CHEN Ting-di, XUE Xiang-hui, TANG Lei
    Acta Photonica Sinica    2019, 48 (10): 1001001-1001001.   DOI: 10.3788/gzxb20194810.1001001
    Abstract404)      PDF (3179KB)(116)       Save

    According to the atmospheric continuous laser beam imaging technology, the corresponding resolution range for the distance between separated transmitter and receiver on bistatic helium lidar system is obtained, as well as the relationship between the single-row CCD pixels and the altitude, and the variation curve of resolution range with different altitudes. Moreover, the corresponding relation between the number of photons received by the system's single-row pixels and the altitude under different metastable helium densities is analyzed, and the signal to noise ratio and relative error varied with altitude are obtained. The simulation results indicate that the signal to noise ratio can be improved by increasing the integration time. In the range of altitude from 400 km to 1 000 km, when the integration time is 2 h and the range resolution is 50 km, the signal to noise ratio is in the range from 10 to 65 and the relative error is less than 10%. These results prove that adopting the bistatic helium resonance fluorescence lidar system can detect the metastable helium density of the 200~1 000 km thermosphere, which provides a reference for further perfecting and optimizing the scheme of the bistatic helium resonance fluorescence lidar system.

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    Photoelectronics Multiplication Organic Photodetecors with Controllable Operating Voltage
    AN Tao, LIU Xin-ying
    Acta Photonica Sinica    2019, 48 (10): 1004002-1004002.   DOI: 10.3788/gzxb20194810.1004002
    Abstract403)      PDF (2727KB)(133)       Save

    The adjustable working voltage of device is realized by changing the ratio of donor-acceptor in the active layer of the organic detector. The influence mechanism of different PC61BM concentration on the hole tunneling injection voltage in PBDT-TT-F:PC61BM:C60 photoelectronics multiplication device was studied. Under the adjacent 600% external quantum efficiency value, by adjusting the concentration of PC61BM, we can obtain a low device operating voltage of -3 V and a high device operating voltage of -6 V. The results show that the hole transport ability and exciton dissociation efficiency of the active layers are changed by adjusting PC61BM concentration, which causes the change of the collection efficiency of hole injection current for anode. Finally, the regulation of device operating voltage is achieved. This paper provides an universal method for obtaining photoelectronics multiplication organic photodetectors with facile fabrication, low and controllable operating voltage.

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    Research Progress on Polarization Maintaining Hollow Core Fiber(Invited Review)
    HONG Yi-feng, WANG Ying-ying, DING Wei, WANG Pu
    Acta Photonica Sinica    2019, 48 (11): 1148010-1148010.   DOI: 10.3788/gzxb20194811.1148010
    Abstract401)      PDF (12593KB)(115)       Save

    Polarization maintaining fiber can reduce the influence of uncontrollable birefringence or polarization mode dispersion caused by environmental disturbance on transmission through artificially introduced high birefringence, and has applications in precision interference sensing, laser systems, optical communication, etc. Compared with traditional solid core fiber which is limited by the intrinsic defect of material, hollow core fiber can confine the optical field in low refractive index air core by specific microstructure design, with low delay, low dispersion, low nonlinearity, high photoinduced damage threshold, anti-interference and high flexibility of filling liquid or gas. Hollow core fiber which have polarization-maintaining feature can not only exert its performance advantages in the above applications, but also show broad prospects in high-power pulsed laser transmission and biochemical analysis application. In this paper, the development of polarization-maintaining hollow core fiber is briefly reviewed, and its design concepts and fabrication techniques are discussed.

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    Achieving High-detection Organic Photodetectors Covering the Visible Range by Using a Ternary Active Layer
    AN Tao, WANG Yong-qiang, ZHANG Jun
    Acta Photonica Sinica    2019, 48 (10): 1004001-1004001.   DOI: 10.3788/gzxb20194810.1004001
    Abstract399)      PDF (5555KB)(153)       Save

    A high detectivity organic photodetector with active layer P3HT:PBDT-TT-C:PC61BM covering the visible wavelength range was prepared by solution spin coating and high vacuum evaporation. The effects of PBDT-TT-C doping P3HT:PC61BM on the optical properties of the active layer films were investigated by atomic force microscopy, UV-visible absorption spectroscopy and fluorescence spectroscopy. It was found that when the mass ratio of P3HT:PBDT-TT-C:PC61BM in the active layer was 8:2:10, the response spectrum of the active layer was broadened to 350~780 nm. The optical responsiveness and external quantum efficiency of the red, green and blue primary colors of the detector under the bias of -1 V reached 422 mA/W, 464 mA/W, 286 mA/W and 83%, 108%, 77%, respectively, and the specific detectivity reached above 1012 Jones. The results show that the organic material with an organic material complementary is doped. On the basis of ensuring the microscopic morphology of the film, By adjusting the mass ratio of the ternary mixed material, not only the carrier generation and transport can be optimized, the photocurrent of the device is improved, but also the crystallization of the thin film can be promoted by the incorporation of the third component, and the dark current of the device can be reduced.

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    Packaging and Integration of Whispering Gallery Modes Optical Microcavity Devices(Invited Review)
    WANG Peng-fei, LI Ang-zhen
    Acta Photonica Sinica    2019, 48 (11): 1148008-1148008.   DOI: 10.3788/gzxb20194811.1148008
    Abstract397)      PDF (3748KB)(295)       Save

    The whispering gallery modes microcavity devices play an important role in modern optics. They have wildly applied prospect in many field such as high sensitivity sensor and low threshold laser. However, they are very susceptible to outside interference such as vibration, temperature and humidity, which is challenging to make them practical. In recent years, the whispering gallery modes microcavity devices for practical uses has caused widely concern and many related studies have been reported. In this paper, the latest research progress on packaging and integration of whispering gallery modes microcavity devices is briefly introduced.

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    Structure Design and Bending Loss of a Novel Fiber for Low Temperature Environment
    CAO Shan-shan, GUO Chao-yang, WANG Zhen, LIU Zhi-zhong, GENG Pei-heng, XU Hai-tao, ZHU Jing, DENG Li, CAO Yong, WEI Wei
    Acta Photonica Sinica    2019, 48 (11): 1148018-1148018.   DOI: 10.3788/gzxb20194811.1148018
    Abstract395)      PDF (2944KB)(65)       Save

    A novel fiber used in extreme low temperature (-70℃) was designed, which includes the core layer, the inner cladding layer, the depression cladding and the outer cladding layer. The relationship between the bending loss and the refractive index difference was studied. By comparing the thickness and modulus of different coating layers, optimizing design of the fiber drawing process, a quartz fiber that can be used in -70℃ for a long time was manufactured. The experimental results show that the additional loss (-70℃) of the fiber at 1 550 nm and 1 625 nm is less than 0.01 dB/km, which provides reliable theoretical and experimental basis for the preparation and industrialization of extreme cold fiber and optical fiber composite overhead ground wire.

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    A Sensitivity-enhanced All-fiber-optic Liquid Refractive Index Sensor Based on Vernier Effect
    ZHAO Yu-xin, JIANG Jiu-xing, YANG Yu-qiang, WANG Yong-guang, LU Jian-da, LIU Jia-cheng
    Acta Photonica Sinica    2019, 48 (11): 1148022-1148022.   DOI: 10.3788/gzxb20194811.1148022
    Abstract394)      PDF (3615KB)(100)       Save

    In order to realize the high sensitivity measurement of the liquid refractive index, a sensitivity-enhanced all-fiber-optic liquid refractive index sensor based on vernier effect is proposed and demonstrated. The sensor is composed of a Fabry-Perot sensing cavity and a Fabry-Perot reference cavity in parallel. The sensing cavity is an open cavity made by offset splicing of single mode fiber, and the reference cavity is a sealed cavity, which is fabricated by fusion splicing of single mode fiber and hollow optical fiber. The free spectral ranges of the two Fabry-Perot cavities are similar, but not equal. Vernier effect is generated when the beams are superimposed via a fiber coupler to achieve the sensitization effect. Experimental results show that the refractive index sensitivity of the proposed sensor is about 9 048.78 nm/RIU, which is about 8 times that of a single sensing cavity. Due to the advantages of high sensitivity, simple structure, easy preparation and low cost, the sensor has potential application foreground in chemical and biomedical domain.

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