Data Acquisition And Processing In Distributed Fiber Sensing System Based On Brillouin Backscattering

Optical fiber sensing technology based on Brillouin backscattering can be used to measure the changes in environmental parameters such as temperature and stress over long distances. And it has such advantages as anti-electromagnetic interference, corrosion resistance and adaption to harsh environments. Therefore, it has been more and more widely applied in the field of environmental monitoring in defense and civilian. At present, many researches about Brillouin sensing focus on the direction of signal acquisition and processing methods. How to extract the weak Brillouin sensing signal from the fiber is also a key issue.In this thesis, the sensing principle based on Brillouin scattering was analyzed and the dependence of Brillouin shift and intensity on temperature and strain was established. Digital signal processing by superposed average method was described in detail. We used microwave radio source to shift the frequency of reference light. We used optical coherent heterodyne detection to reduce the signal frequency, and distinguish the Brillouin scattering signal from the Rayleigh scattering in the fiber. And we used Altera's Nios ? soft-core processor as the digital signal processing CPU. Moreover, FPGA was used to control the digital acquisition and denoising, and transfer data to computer client software for data processing and analysis via the serial port protocol. We wrote a MATLAB program for users to control data acquisition and processing in the system.The temperature measurement of a 30km-long optical fiber was realized by this system. The results of experiment show that the system works stably and safely and conforms to the expected design.