Design Of Distributed Optical Fiber Sensing System Test Platform

Distributed fiber sensing technology derives the temperature and strain distribution on the fiber by detecting the intensity of the scattered light at each location along the fiber.Brilouin Optical Time Domain Analysis(BOTDA)is a distributed optical fiber sensing technology,which is suitable for long-distance,large-range and high-sensitivity distributed optical fiber sensing system.It can realize accurate and real-time measurement of temperature and strain on optical fiber,which has important research significance and practical value.The dissertation studies the Brillouin scattering effect in fiber and the sensing principle of BOTDA.Based on the signal characteristics of BOTDA sensing system,a distributed optical fiber sensing system test platform is designed.The main research contents and innovations of the dissertation are as follows:(1)Design of FPGA-based distributed optical fiber sensing system test platformBased on the research of BOTDA sensing system,this dissertation proposes an implementation scheme of distributed optical fiber sensing system based on FPGA.According to the functional requirements of each module in the scheme,the dissertation carries out the hardware circuit design of FPGA,high-speed ADC and frequency sweeper,as well as the system logic design based on FPGA.(2)A frequency scanning module implementation scheme based on frequency synthesis technologyAccording to the requirements of the frequency scanner with adjustable frequency and step size,the scheme of frequency sweep signal generated by broadband RF frequency synthesis chip LMX2594 is proposed,and the hardware circuit is designed.LMX2594 can generate any frequency in the range of 10MHz to 15GHz without the use of internal multiplier.The built-in 32-bit N frequency divider can satisfy the sweep output with frequency step of 1Hz.The output frequency and step length can be controlled by programming,which provides the hardware support for the realization of Brillouin scattering spectral feature extraction algorithm.The results show that the designed frequency scanner can meet the requirements of the system.(3)A scheme for feature extraction of Brillouin scattering spectrum based on half-interval search sweep methodDue to the system measurement time of Brillouin scattering spectral feature extraction algorithm based on cross-correlation algorithm is long,this dissertation proposes a Brillouin scattering spectral feature extraction algorithm based on half-interval search sweep method.The traditional algorithm sets the output frequency of the sweeper to step-by-step growth,while the optimization mainly sets the output of frequency sweeper combined with the idea of binary search,which shortens the range of frequency scanning and obviously shortens the measurement time of the system.Based on the hardware foundation of the frequency sweeper in(1),the optimization algorithm can be implemented.The two algorithms are used to simulate the experimental data collected under normal temperature and heating condition.The results show that both algorithms can accurately and effectively measure the temperature,and the optimization algorithm has a significantly shorter system measurement time than the traditional algorithm.