Research On Interference Distributed Optical Fiber Vibration Sensing System

Distributed optical fiber sensing system is the application of strain measurement characteristics of optical fiber. It has been widely applied in aircraft, civilian-military security, pipeline leak detection and other fields. This thesis mainly researched distributed optical-fiber vibration sensing system. Based on the basic Sagnac structure, we designed a non-equilibrium single fiber Sagnac sensing system which is structurally similar to Mach-Zehnder interferometer. The results of research as shown below.Firstly, the measurement capability of non-equilibrium single fiber Sagnac sensing system was analyzed, and the mathematical model simulation for intensity distribution function of vibration position in varying frequency were undertaken. Compensated the offset by using delay-ring to minimize the distraction, and improved the signal noise rate by using polarization maintaining optical fiber after analyzing the noise sources of optical path structure.Secondly, the MCU-based optical source driving circuit implemented constant power source and invariable operating temperature for SLD module. The design approach for optical signal receiver analog front-end and signal processing unit were discussed in detail. Meanwhile, the methods of noise suppression and impedance matching in signal chain were also presented. The technique concerned with this part, including interface of sensor, signal conditioning, EDA simulation and PCB layout design.Finally, the firmware of optical source driver and the digital signal process program were designed, and a simple TCP/IP client was written. Invariable temperature and constant power output depended on digital PID controller. In addition, based on DSP, a FIR digital filter was designed to wipe off the interference signal, and a web service was realized at the same time to support of data exchange with PC.This thesis made a useful attempt to develop low-cost and practical applications of fiber sensor, and has good potential with hardware performance and secondary development.