Research On Optimal Design Of ?-OTDR Distributed Optical Fiber Sensing System

Compared with the common point type optical fiber sensing technology,the distributed optical fiber sensing technology has many advantages,such as long-distance,continuous detection and so on.Among them,as a typical representative of distributed optical fiber sensing technology,phase sensitive time domain reflectometer(?-OTDR)is widely used in many fields,such as perimeter security,bridge and railway safety monitoring,transmission line galloping early warning and so on.The performance of ?-OTDR sensor system mainly include sensing distance,spatial resolution and frequency response range.In this dissertation,from the perspective of extending the sensing distance of ?-OTDR sensing system,the fiber grating and ?-OTDR sensing system are combined to improve the signal-to-noise ratio of the scattered signal,so as to extend the sensing distance of ?-OTDR sensing system.The main research contents are as follows:A ?-OTDR distributed optical fiber sensing system based on 3×3 coupler demodulation method is built;the experimental research on the phase demodulation of long-distance optical fiber vibration signal is carried out by using the system to test its detection ability in different optical fiber length positions.By connecting the fiber grating into the sensing fiber,the signal-to-noise ratio of the scattered signal in the long-distance position of the fiber is improved,and the detection ability of the ?-OTDR sensing system for the vibration signal in the long-distance position of the fiber is improved,which is verified by relevant experiments.The influence of the signal-to-noise ratio of the scattered signal on the phase demodulation method of the 3×3 coupler is simulated and analyzed.When the signal-to-noise ratio is low,the demodulation amplitude will have a large gap with the real amplitude,and when the signal-tonoise ratio increases gradually,the demodulation effect will be improved;when the scattered signal has a proper signal-to-noise ratio,the reflectivity of the fiber grating required for sensing different positions of the fiber is simulated and analyzed,it can provide theoretical support for choosing fiber grating with appropriate reflectivity and increasing the maximum sensing distance of the system.