Research On Phase Sensitive Time Domain Reflection System Based On Clock Homologous I/Q Demodulation

Distributed Optical Fiber Sensing Technology(DOFS)can continuously measure the physical quantity on the entire sensor fiber,which has attracted the attention and research of experts and scholars at home and abroad.As a fully distributed optical fiber sensing technology,it has high sensitivity and many advantages such as strong corrosion resistance,wide dynamic range,and simple structure.It also has great application prospects in a wide range of perimeter security,oil and gas pipeline safety monitoring,large-scale structural health monitoring and other fields.However,in the process of demodulating the phase,due to non-homogeneous inconsistency between the modulated signal and the mixed signal,the residual frequency is generated,which affects the accuracy of the phase demodulation.Therefore,how to effectively avoid the generation of residual frequencies in the system and improve the system's accuracy in identifying,extracting,and locating the disturbance signals is of crucial importance to the development of the system.1.This paper introduces the structure,applications and prospects of several detection systems based on Rayleigh scattered light,and focuses on the research progress of phase demodulation.the structure of the system and the basic principle of detection are analyzed.2.in the next chapters,the thesis introduces several kinds of phase demodulation methods,analyzes the advantages and disadvantages and proposed a method for clock homologous I/Q demodulation.Then it theoretically analyzes how the residual frequency generates in the demodulation process,and how the final demodulation result is affected.The clock homology I/Q demodulation method is applied to eliminate the influence of residual frequency by making the acousto-optic modulator modulating signal,chopping signal and I/Q mixing signal clock homologous.3.A kind of clock homologous device is designed to ensure,through the design of the acousto-optic modulator driver,the phase consistency of the modulator before and after the chopping wave,improve the accuracy of the phase demodulation and perform the subsequent homologous phase I/Q demodulation,which lays tyhe foundation of the structure.4.An experimental measurement of the clock homologous I/Q demodulation method was performed..In the experiment,the clock homologous I/Q demodulation structure is used to locate the sinusoidal disturbance signals at the 5km and 9km positions in the sensing fiber.Thephase demodulation result of the clock homologous I/Q structure is up to 0.994,0.991,and the root mean square error is 0.116,0.141,The coincidence degree between the phase demodulation result and the sine perturbation waveform is 0.955,0.906,and the root mean square error is0.276,0.457..It shows that the clock homology phase demodulation result is more accurate than the non homologous phase demodulation,which has successfully improved the accuracy of system detection.5.the phase demodulation of the phase sensitive time domain reflectometry system is analyzed and summarized,and the prospect of improving the detection performance of the system is prospected.