Research On Distributed Fiber-Optic Sensor System Using Synthesis Of Optical Coherence Function

Optical fiber is used as the sensing element and transmission medium in the distributed fiber-optic sensor system. The system can gain the information measured among the sensing optical fiber which will be changed with the time and space.We research into a distributed fiber-optic sensor system based on synthesis of optical coherence function (SOCF). We analyze the fundamental principle of the SOCF in detail and focused on two methods which can synthesis periodical coherence peaks, one uses stepped square wave for frequency modulation, the other uses sinusoidal wave for frequency modulation. By changing the modulation frequency the period of the coherence peak can be changed and the location of the coherence peak can be shifted to realize the distributed information measurement beyond the coherence of the fiber.We build the system called distributed optical coherence domain reflectometer based on SOCF and perform a series of experiments than we successfully locate the reflected point at the fiber end and gain the length of the testing fiber with the error within1meter. We improve the system which can shift the coherence peaks continuously and quickly. We use one computer to control the Signal Generator for modulating the frequency by GPIB bus and to control the Spectrum Analyzer for acquiring the beat frequency power synchronously. In this way we realized the distributed sensing system. The reflecting information of the fiber is related to the power of demodulated signal. The six reflection points at10.225km are located precisely with a spatial resolution of2.20m. Then we measure the return loss of the six reflection points and verify the power of demodulated signal is related to the return loss.