Research On Optical Fiber Distributed Broadband Acoustic Sensor Technology Based On Time Division Multiplexing

Distributed optical fiber acoustic wave sensing system has the advantages of high sensitivity,many measurement points,and the ability to realize distributed sensing.It has important application value in major infrastructure health testing,oil and gas exploration,and perimeter security.However,in the distributed optical fiber sensing system,there is a problem that the sensing distance and the response bandwidth are mutually restricted.As the sensing distance of the system increases,the frequency response bandwidth decreases,which limits its application in the field of high-frequency vibration signal detection.In order to solve this problem,this article only needs to work as follows:Firstly,aiming at the contradiction between sensing distance and response bandwidth in distributed optical fiber sensing system,this paper proposes a "Broadband Response of Optical Fiber Distributed Acoustic Sensor Based on Time Division Multiplexing ".The system uses a multi-wavelength narrow linewidth laser,WDM,circulator,and delay fiber to achieve the combination of two sections of ~ 1.04 km sensing fiber,so that the optical signals on the two sections of sensing fiber reach the photodetector in the time domain to form time-division multiplexing.The system uses an 80 kHz optical pulse repetition frequency and a sampling rate of 120MSa/s for simultaneous acquisition.The 40 kHz vibration signal is effectively detected on the ~ 2.08 km sensing fiber,and the signal to noise is relatively high.Compared with the traditional ?-OTDR system,the effective detection frequency range of the system is theoretically doubled.In addition,in order to verify the response characteristics of the "Broadband Response of Optical Fiber Distributed Acoustic Sensor Based on Time Division Multiplexing ".For the application in pipeline leak detection,this paper designs a "gas pipeline leak simulation device" and use the system to detect the leakage signals under different transmission pressures.Experiments show that the system can not only detect the weak vibration signal when the gas transmission pressure in the pipeline is 0.2MPa,but also the frequency spectrum of the detected leakage signal includes two parts of low frequency broadband and high frequency single frequency signals,and the signal strength increases with the increase of the gas transmission pressure.The “Broadband Response of Optical Fiber Distributed Acoustic Sensor Based on Time Division Multiplexing” proposed in this paper can improve the response bandwidth of traditional ?-OTDR system,so that it can be applied to a wider range of fields.