Research On The Key Technology Of Optical Fiber Vibration Sensor

Optical fiber sensing technology has wide applications and great significance in the areas such as border security,oil and gas pipeline monitoring and large bridge concrete buildings' safety.The distributed optical fiber vibration sensor discussed in this paper has the advantages of low cost,large sensing range,high sensitivity and free of EMC issue for using the common single mode fiber.We combined the technology of optical signal processing and FPGA data processing,which is especially suitable for flammable,explosive,large area and other special environment.The optical fiber sensor system based on the back scattering and light interference is sensitive to vibration signal.We developed a low-cost laser module suitable for sensing application,having an output power of 130 m W with narrow-linewidth bandwidth.According to the structure of the interference optical path,the OTDR optical signal receiving and processing module is developed and realized the functions including signal receiving,processing,amplifying and filtering.As to demodulate the vibration signal,we developed the signal processing module by using the FPGA,having advantages of high-speed data flow processing in parallel.Vibration signal processing is achieved by OTDR optical signal receiving and processing module.In the long-distance distributed vibration sensing experiment,the method of segmented gain compensation is proposed,which uses the voltage controlled operational amplifier for segmented amplification to compensate the optical signal attenuation along the distance of the optical fiber.It greatly improved the signal-to-noise ratio of the tail signal of the OTDR trace.In EDFA power amplification experiment,it is found that the distortion of optical pulse signal may affect the the systematic performance.Finally,experimental results of the sensor's performance test show that the single point location accuracy is about ±15 m,multi-point location accuracy is about ±30 m.The sensor system supports multi-point simultaneous vabration measurement.Meanwhile,the sensing range is ? 20 km with response time < 2 s.The proposed senor system has potential applications in the field of perimeter security,pipeline protection and other large areas' monitoring applications.