Research On Distributed Optical Fiber Vibration Sensing System Based On POTDR

The distributed optical fiber vibration sensing system based on polarization sensitive optical time domain reflectometer(POTDR)has the advantages of continuous distributed monitoring,fast response speed and high detection sensitivity,and has important application value in the field of health monitoring of large-scale infrastructure.However,the present POTDR system still has the problems of low signal-to-noise ratio(SNR)and high misdiagnosis rate.On the hand,because of the polarization superposition effect and the inherent birefringence of the fiber,the state of polarization(SOP)changes caused by vibration in the fiber will continue to affect the SOP of light after disturbance position.And the sensing signal fluactuates along the fiber.Therefore,POTDR technology still has the problem of high misdiagnosis rate and multi-disturbance event superposition crosstalk.On the other hand,the low SNR makes it difficult to improve the dynamic range,spatial resolution and sensitivity of the system to meet the needs of practical applications.This paper proposes solutions to the above two problems,and the feasibility and performance of the scheme are verified through the establishment of simulation and experimental system.The specific work is described as follows:This paper presents a POTDR sensing system using probe pulses with ergodic SOPs.This method can effectively suppress the random fluctuation of sensing signal caused by the inherent birefringence of the fiber,and reduce the standard deviation of sensing signal.This paper deduces the feasibility of the method in theory,and verifies it by simulation and experiment respectively,and successfully solves the problem of high misdiagnosis rate and superposition crosstalk of multiple disturbance events.And detect multi disturbance events with the same vibration frequency by using POTDR technology.In order to further improve the SNR of distributed optical fiber sensing system,this paper also presents a vibration sensing technology of POTDR based on UV exposure.The UV laser is used to directly expose the single-mode fiber.It is found that the Rayleigh scattering intensity of the fiber after UV exposure can be improved by nearly one order of magnitude compared with the traditional single-mode fiber.A POTDR system based on equispaced point exposure optical fiber is designed and fabricated.The experiment verifies the feasibility of uv-exposure optical fiber to improve the SNR of distributed optical fiber vibration sensing system.The SNR of the system is improved by 9.5 dB.