Research On Near Zero Difference Coherent Optical Time Domain Reflection Technology

With the rapid development of optical fiber sensing technology,people's requirements for sensing performance are increasing.Optical fiber sensing technology based on coherent optical time domain reflection has the advantages of high sensitivity,high resolution,anti-electromagnetic interference,and corrosion resistance.Therefore,this technology has begun to attract the attention of researchers.Coherent optical timedomain reflection sensing technology has been widely used in key areas such as national defense,security,and environmental monitoring.This thesis carries out research on the mechanism and key technologies of distributed optical fiber sensing based on coherent optical time domain reflection technology.The main research contents are as follows:(1)Analyzed different types of distributed optical fiber sensing technologies,and briefly introduced their sensing principles and development status,as well as their application prospects in different fields.(2)An overview of the basic principles of coherent optical time-domain reflection technology,the theoretical analysis and derivation of the backscattered light intensity change in the optical fiber,the sensing mechanism and the backward direction of the change of different physical quantities caused by fiber failure The combination of phase changes of scattered light leads to the mechanism of coherent light time-domain reflection technology.(3)A near homodyne coherent detection method based on quadrature phase detection is proposed.The method uses a 90° mixer for coherent demodulation,which can detect signals within the bandwidth of the transmitted pulse signal,which significantly improves the signal-to-noise ratio and sensitivity of the system.This paper designs a distributed optical fiber sensing system based on coherent optical time domain reflection technology,and initially verifies the feasibility of the system's operation.It is expected to improve the fault location accuracy and reduce the system's false alarm rate.(4)According to the structure and principle of fiber grating laser,a single-frequency pulsed fiber laser with an output wavelength of 1540 nm was designed and fabricated.Using a high concentration of erbium-doped fiber as the active medium,a 0.1nm bandwidth Bragg grating as the resonant cavity,and a single-mode fiber-coupled semiconductor laser as the pump source to form a DBR fiber laser,the self-adjusted Q pulse laser output is obtained,and the Test its output characteristics.The intensity noise and noise reduction method of the local oscillator laser are analyzed.