Research On Signal Processing Of Distributed Optical Fiber Vibration Sensing System

Distributed optical fiber sensor uses optical fiber as the sensing medium for static strain,temperature,pressure and dynamic vibration measurement.They have anti-electromagnetic interference,corrosion resistance,electrical insulation,high security,good concealment.Among various optical fiber sensors,the sensor system based on phase sensitive optical time domain reflectometer ?-OTDR(Phase Optical Time-Domain Reflectormeter)has attracted more attention as a dynamic vibration sensor due to its high sensitivity,large dynamic range,and fully distribution.In order to achieve better sensing property,this paper has carried out research on signal processing and practical technology based on ?-OTDR.The main work is as follows:This paper introduces the principles and applications of OTDR(Optical Time-Domain Reflectormeter)and interferometer technology in distributed optical fiber sensing,and analyzes the principle and main performance of the phase demodulation ?-OTDR technology.Based on analyzing and comparing the characteristics and demodulation performance of phase carrier demodulation PGC(Phase Generated Carrier)technology and 3 × 3 coupler demodulation technology,a new demodulation structure is proposed in this paper.By using PGC demodulation algorithm and 3 × 3 coupler to solve the problem of time delay between the carrier signal and the disturbance signal.At the same time,in order to further improve the signal-to-noise ratio and stability of the system,the effects of the differential crossover DCM(Differential and Cross Multiplying)algorithm and the arctangent Atan(Arctangent)algorithm on the demodulation effect of the new structure and the traditional structure under time-delay conditions are compared.The effects of delay and different linewidth lasers on demodulation are analyzed.The results show that the new structure with the arctangent demodulation algorithm has better demodulation accuracy and stability and is not affected by time delay.Compared with a 1MHz linewidth laser,a 3k Hz linewidth laser can obtain higher signal noise ratio.By analyzing the main optical devices and performance in the ?-OTDR sensing system,a new ?-OTDR fiber sensor structure for all of the distance is proposed to solve the optical fiber front-end vibration transmission caused by the saturation of the photodetector.And the low power cannot meet the long-distance detection.Experiment results show that the measurement distance is about 40 km.This paper analyzes three signal processing methods of wavelet threshold denoising,wavelet energy spectrum extraction feature algorithm,and vector machine classification algorithm,and proposes that using these three algorithms to pre-process three types of vibration events collected by the ?-OTDR sensing system and feature extraction classification.The experiment results show that the underground cable intrusion warning system scheme provided in this paper can achieve the average classification accuracy rate of 98.3%.And the signal processing experiment provides a reference for subsequent signal pattern recognition.The research results also accelerate the field of the optical fiber sensing in early warning security and practical applications.