Design And Implementation Of High-speed And Long-distance OFDR Sensing System

Today,with the rapid development of 5G technology,Internet of Things and big data,whether sensors can accurately obtain external information plays a decisive role in the interconnected society of everything.Optical frequency domain reflection(OFDR)distributed optical fiber sensing technology has ultra-high spatial resolution and sensing accuracy,which can be applied to structural health monitoring of DAMS,Bridges,pipelines,electrical circuits,aerospace and ships to realize early warning of structural damage and location of damaged parts,and ensure the safe operation of equipment.In the existing OFDR studies in China,most OFDR sensor data are processed by software algorithms on the computer side,and the calculation takes several minutes.Therefore,real-time sensing cannot be carried out over long distances or with high spatial resolution.In this paper,OFDR data demodulation algorithm is transplanted to FPGA platform,hardware data processing algorithm at millisecond level is designed,and an integrated high-speed OFDR sensor system is realized,which consists of optical signal transmitting and receiving,data acquisition and high-speed processing,real-time display and other processes.The main contents of the paper are as follows:1.Study the strain and temperature sensing theoretical model of OFDR system,analyze the influence of nonlinear frequency sweeping of tunable laser,and the corresponding compensation scheme;The influence of laser parameters on OFDR sensor system is studied.The joint control scheme,hardware logic design and implementation of laser frequency sweep and OFDR system data acquisition are designed.2.Design OFDR data processing algorithm based on FPGA platform,including selection of FPGA chip according to algorithm complexity,data acquisition and storage logic design,large point two dimensional Fast Fourier Transform(FFT)algorithm logic design,sliding window crosscorrelation calculation,etc.Finally,in order to further improve the FPGA data processing speed,this paper designs two FPGA to process OFDR sensor data jointly based on QSFP28 optical port and Aurora protocol,and carries out experimental tests.3.Completed the construction and experimental testing of high-speed and long-distance OFDR sensing system,including the construction of main interferometer and auxiliary interferometer,the selection of laser,photoelectric detector,acquisition card and other key devices,and the realtime display of sensor results based.on Labview serial host computer,etc.The distance of OFDR sensor system designed in this paper can reach 50 meters.Spatial resolution up to 3mm;Under the premise of 50 meters sensing distance and 6mm spatial resolution,the maximum sensing speed can reach 100ms.