Table of Content

31 March 2020, Volume 38 Issue 2

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Optical Fiber Sensors Technology

Progress in Research of Brillouin Optical Time Domain Analysis for Dynamic Strain Sensing

ZHU Tao, ZHENG Hua, ZHANG Jingdong

2020, 38(2):  197-214.  doi:10.3969/j.issn.0255-8297.2020.02.001

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Brillouin optical time domain analysis (BOTDA) has wide application prospects in health monitoring of large infrastructure and condition monitoring of aircraft, since it is capable of sensing distributed strain over long distance with high spatial resolution and accuracy. However, the sensing speed of conventional BOTDA is fairly slow and hardly realize dynamic strain measurement due to its frequency sweeping process. Aim at this problem, this paper reviews the research progress of BOTDA for dynamic strain sensing in recent years, including slope-assisted BOTDA (SA-BOTDA), fast BOTDA (F-BOTDA), sweep free BOTDA (SF-BOTDA) and dynamic BOTDA based on chirped pump/probe. The advantages and disadvantages of these technologies are discussed, and the development prospects of BOTDA for dynamic sensing are estimated as well.

Distributed Optical Fiber Sensing Technology and Its Application in Coal Mine Safety Production

LI Shinian, ZHANG Xuping, SONG Hong, CHEN Jian, ZHANG Yixin, LU Jinbo, ZHAO Xiaojing

2020, 38(2):  215-225.  doi:10.3969/j.issn.0255-8297.2020.02.002

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Coal is the main source of energy in China, and coal mine geological monitoring is an important guarantee for the safe production of coal mines. Distributed optical fber sensing technology has the advantages of sensing continuity, high precision, antielectromagnetic interference and corrosion resistance, and has been applied in coal-mine geological monitoring in recent years. First, this paper introduces the principle of Brillouin optical time-domain reflectometry (BOTDR) technology and its applications in the coal-mine geological monitoring. Second, a practical application of BOTDR to monitor the deformation of coal-mine goaf is demonstrated. It shows that the distributed optical fber measurement could sufciently meet the requirements of coal-mine geological monitoring and has a good application prospect.

Research Progress of Fiber Micro Cavity Fabry-Perot Interference Sensors

ZHAO Chunliu, LI Jiali, XU Ben, GONG Huaping, WANG Dongning

2020, 38(2):  226-259.  doi:10.3969/j.issn.0255-8297.2020.02.003

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Fiber microcavity sensors have gained widespread attention in the feld of optical fber sensing due to their inherent safety, small size, low cost, and resistance to electromagnetic interference. Fiber microcavity Fabry-Perot interference sensors features with multiple measurable parameters and the capability of simultaneous measurement of multiple parameters. This article reviews the research progress of the fber microcavity Fabry-Perot interference sensors in various sensing scenarios, such as temperature, pressure, liquid refractive index, hydrogen concentration, organic volatiles concentration and so on, and introduces the manufacturing method, sensing principle and experimental results of the sensors in detail.

Research on Temperature Sensors Based on Microstructured Fiber

GENG Youfu, LI Xuejin

2020, 38(2):  260-278.  doi:10.3969/j.issn.0255-8297.2020.02.004

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A variety of microstructured fber temperature sensors, including intermodalinterference types of Mach-Zehnder, Michelson and F-P interferometers and fluorescence type based on demodulation method, have been studied comprehensively and profoundly.The corresponding theories, sensor systems and functional devices are constructed. Among these works, a novel multi-parameter fluorescence fber temperature sensor with a new signal processing method based on the strong correlation between excitation light and fluorescence was proposed. And based on a small segment of liquid-flled microstructured fber, an all-fber Mach-Zehnder temperature fber sensor with ultrahigh sensitivity of -1.83 nm/℃ was developed. In addition, a Michelson-type high temperature fber sensor with a tiny probe size of only 1.03 mm was achieved by utilizing a high-order mode in all-solid photonic bandgap fber. Moreover, a grape-type microstructured fber F-P interferometer sensor for high temperature measurement was proposed and demonstrated. The high temperature sensor performs a sensitivity of 17.7 pm/℃ at 1 570 nm and a high measurable temperature of up to 1 000 ℃.

Progress in High Resolution Demodulation Techniquesfor Wavelength-Encoded Optical Fiber Sensor

CHEN Jiageng, LIU Qingwen, ZHAO Shuangxiang, He Zuyuan

2020, 38(2):  279-295.  doi:10.3969/j.issn.0255-8297.2020.02.005

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This paper introduces the latest progress in the demodulation techniques of high resolution wavelength-coded optical fber sensor, which are applicable to high performance optical fber strain sensor and sensor array with sub-nano strain resolution. This paper frst reviews and discusses the classical FBG strain sensing technique and introduces the optimized sensing elements in high resolution optical fber strain sensing systems; then presents the authors' recent works on demodulation methods for high resolution optical fber sensors, including a feed-forward frequency-swept laser linewidth compression technique and a closed-loop cyclic interrogation technique in detail. Finally, we introduces an implementation of the high resolution optical fber sensors in the observation of crustal deformation, providing an example for other related research and application scenarios.

New Type of Microstructure-Fiber Distributed Acoustic Sensing Technology and Its Applications

LIU Deming, HE Tao, XU Zhijie, SUN Qizhen

2020, 38(2):  296-309.  doi:10.3969/j.issn.0255-8297.2020.02.006

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A new distributed microstructure optical fber (DMOF) and a distributed acoustic sensing technology based on the DMOF are introduced in this paper. The DMOF is a new type of longitudinal microstructure fber formed by continuously preparing microstructure scattering unit in the core of ordinary communication optical fber through precise lithography technology. The microstructure-fber distributed acoustic sensor (MFDAS) based on this new type of DMOF has superior performance such as high sensitivity,large monitoring scale and wide frequency response. The key technologies and research progress of the MF-DAS are introduced in this paper, including that the signal-to-noise ratio of the MF-DAS sensing signal is increased by enhancing the microstructure light scattering, the near-far-end signal difference of the MF-DAS is reduced by the microstructure fber link equalization, and the response broadband of detectable distributed sound-wave is improved signifcantly by the microstructure optical time domain reflection (M-OTDR) and the time slot multiplexing of microstructure optical time domain reflection. The new MF-DAS features with large-scale, high-sensitivity and broad response bandwidth in the acquisition of sound wave information, and shows a very broad application prospect in the injury detection of critical infrastructure and the security monitoring of external intrusion.

Few-Mode Fiber Long-Period Gratings—From Mode Conversion to High Sensitivity Fiber-Optic Sensing

ZHAO Yunhe, LIU Yunqi

2020, 38(2):  310-338.  doi:10.3969/j.issn.0255-8297.2020.02.007

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Few-mode fber (FMF) long-period grating (LPG) with advantages of good wavelength selectivity, low insertion loss, flexible structure, high integration and compatibility with optical fber systems,is an effective means to realize mode conversion and vortex mode regulation in the FMF, which have great potential for applications in the optical fber communications and fber-optic sensing. This paper presents the research progress of FMF-LPG in mode conversion and optical fber sensing. Firstly, the mode coupling principle and fabrication methods of FMF-LPG are introduced. Then, the mode converters based on FMF-LPG including standard LPG and helical LPG are investigated. Finally, the working principle and implementation method of fber-optic sensors based on FMF-LPG are demonstrated.