Research On Performance Optimization Based On BOTDA Optical Fiber Sensing System

Brillouin Optical Time Domain Analysis(BOTDA)sensing system is based on Brillouin scattering effect in fiber optics that can monitor external temperature or stress changes in tunnels,oil pipelines and bridges.As one of the key technologies in the filed of optical fiber sensing,BOTDA sensing system has great significance as well as broad application prospects for the structural health of large civil engineering such as dams and the monitoring of surrounding safety protection.Because the Brillouin scattering signal is very weak,the system noise has a great influence on the detection results,so the optimization of BOTDA sensing system has become a research hotspot in this filed.With the continuous maturity of related technologies and the increasing demands for sensing,how to further reduce the interference of system noise on scattered signals,ensure the accuracy of detection while reducing the amount of data processing operations for real-time monitoring and positioning,optimize the system structure to reduce the impacts of the devices to the detection results is an urgent problem to be solved in the current BOTDA technology research.In this paper,a Lifting Wavelet Transform-Gaussian average joint filtering algorithm,a Spatial sampling-Cross correlation BFS extraction algorithm,a new experimental structure keeping pump pulses flat are proposed by studying the related problems of BOTDA sensing system and analyzing the performance of the related algorithms.These works and results are as follows:Firstly,based on the Brillouin scattering principle in fiber and learning of BOTDA system-monitoring principle,the simulation model of BOTDA fiber sensing system is established and the conventional experimental system is studied.Secondly,a lifting wavelet denoising-Gaussian joint filtering algorithm based on lifting wavelet transform is proposed,and the selection of related parameters of the algorithm is discussed.The signal-to-noise ratio of the new algorithm is 14.6dB higher than that of the conventional one-generation discrete wavelet transform,which is 2.78dB higher than that of the ordinary one-dimensional lifting wavelet.The signal-to-noise ratio is improved obviously,which is beneficial to the optimization of the performance of the BOTDA system.Thirdly,a spatial sampling-cross-correlation convolution BFS extraction algorithm is proposed with analysis of the conventional cross-correlation convolution(XCM)algorithm in terms of BFS extraction accuracy and computational complexity.This algorithm is based on the conventional XCM extraction BFS algorithm by the spatial resolution and temperature threshold of the sampled data to ensure the BFS extraction accuracy while reducing the computational complexity of the system,shortening the data operation time,and greatly ensuring the real-time performance of the system.At last,A new BOTDA sensing system scheme was proposed and experimentally demonstrated.In order to ennsure the flatness of the waveform of the encoded pulse amplified from the EDFA,this scheme pre-depletes the number of particles accumulated by the EDFA during the amplification of the pump pulse by additionally introducing a DC beam into the pumping optical branch of the system.Compared with the ordinary BOTDA system using single-wavelength pump light structure,this dual-wavelength pumping light scheme can ensure the effective power of the system pumping pulsed light and improve the signal-to-noise ratio of the system.