Research On Key Technology Of Distributed Optical Fiber Dynamic Strain Sensing

Brillouin optical time domain analysis technology(BOTDA)can obtain the parameters along the optical fiber in one measurement.It has been widely used in the safety monitoring of railways and natural gas pipelines.However,due to the long measurement time,the practical application is greatly restricted.In order to realize the dynamic measurement of strain,this paper firstly establishes the theoretical model of the BOTDA system,and conducts research on the denoising algorithm and demodulation algorithm to improve the measurement speed of the BOTDA system,but it cannot fundamentally solve the dynamic measurement problem;this paper also discusses the optical frequency comb scheme Carrying out theoretical analysis and simulation to verify its dynamic measurement capability,and at the same time designing an optimization scheme for dynamic measurement based on the BOTDA system,which greatly improves the measurement speed of the BOTDA system and has the capability of dynamic measurement.The main contents of the paper are as follows:1.This article explores the internal relationship between Brillouin scattering and strain/temperature through the study of the formation mechanism of Brillouin scattering.Analyze important evaluation indicators such as the spatial resolution,measurement accuracy and dynamic range of the BOTDA system.Through the study of the system measurement time,the factors limiting the dynamic measurement of the BOTDA system are analyzed.2.Carried out the research on denoising algorithm and demodulation algorithm of BOTDA system.The Gaussian filtering algorithm and the wavelet threshold denoising algorithm are theoretically analyzed and simulated,and the two algorithms are compared to improve the signal-to-noise ratio of the Brillouin signal to reduce the system's demand for averaging times.For the demodulation algorithm of Brillouin frequency shift(BFS),the principles of Lorentz algorithm and BP neural network algorithm are analyzed and simulated.The demodulation error and demodulation speed of the two algorithms are compared,and the BFS solution is optimized.Adjust the speed to reduce the system measurement time.3.Carried out experimental research of BOTDA system.The traditional scheme is optimized using the joint filtering method and the BP neural network algorithm.In the experiment,the spatial resolution of 4m is obtained,and the measurement time is 35 s.Compared with the traditional scheme,the measurement time of several minutes is improved to a certain extent,but it is still not possible.Fundamentally solve the measurement speed problem of the BOTDA system.4.Carried out the analysis and design of the dynamic strain sensing system.In view of the dynamic measurement capability of the digital optical frequency comb-based sensing scheme,theoretical research and simulation verification are carried out.The theory analysis of self-coherent heterodyne detection technology and 3x3 coupler demodulation technology is carried out,combined with the two technologies,the BOTDA system is designed,the strain dynamic measurement system is designed,and the demodulation algorithm is simulated and verified on MATLAB.5.Carried out experimental research on dynamic strain sensing system.Using700 m optical fiber for strain experiment,the measured spatial resolution is 4m,and the measurement time is 1.4s.Compared with the traditional scheme,the measurement speed has been greatly improved,and it has the ability of dynamic measurement.