Design And Implementation Of Real-time Brillouin Optical Time Domain Analysis System Based On Digital Optical Frequency Comb

In recent decades,the distributed optical fiber sensing system based on Brillouin optical time domain analysis(BOTDA)has been widely used in the structural health detection of infrastructure due to its advantages of long sensing distance,high resolution and distributed measurement.However,the functions of signal generation,data collection and data processing in traditional BOTDA systems are separated.On the one hand,these separated systems prevent themselves from being highly integrated;on the other hand,it makes it hard to achieve real-time measurement due to the mismatching of the data rate and format between instruments.Although a small number of integrated BOTDA systems have been used for practical applications,however,due to the frequency-sweeping characteristic,the measurement time of these systems is long when the sensing distance is long and the resolution is high,making them cannot meet the requirements of aviation,national defense and other application scenarios with high real-time requirements.Therefore,in this paper,a real-time BOTDA system based on digital optical frequency comb(DOFC)is proposed.Firstly,in order to solve the problem that most BOTDA systems cannot achieve real-time measurement due to the mismatched data interfaces of instruments,an integrated hardware architecture and corresponding interfaces are designed.Secondly,based on the designed hardware system,DOFC probe signal and pump signal are optimized,so that the system can not only avoid the frequency-sweeping operation but also reduce the cost.Furthermore,for the sake of the real-time processing of 20 Gbps sensing data,the data processing is optimized.The specific optimizations include: 1)A fast frame synchronization algorithm based on incremental updating is proposed,which reduces the computational complexity by more than 98% compared with the standard frame synchronization method.2)The function of the data processing is divided reasonably,and the parallel sub-function modules and pipelined data processing flow are designed according to the characteristics of field programmable gate array(FPGA),so that the real-time data processing of the system can be realized.The experimental results show that the designed real-time BOTDA system can carry out real-time distributed temperature and vibration measurements for a long time on 9.2 km sensing optical fiber,and a complete measurement time(including data acquisition and processing)is only 120 ?s,which is the highest index that can be achieved in the same type of technology at present,means it can meet the real-time requirements.