Research On Distributed Vibration Sensing Technology Based On Combination Of Laser Interference

With the continuous expansion of China's major infrastructure construction scale,safety has gradually become the focus of people's attention,There is an urgent need for effective means to achieve long-term and effective monitoring of the safety of major infrastructures such as high-speed rail,airports,bridges,power stations and so on.Distributed optical fiber vibration sensing technology can monitor and measure vibration information in a long distance continuously.Simultaneously,it has the excellent characteristics of anti electromagnetic interference,high detection sensitivity,high temperature resistance and so on and thus suitable for wide range monitoring applications.This paper aims at the important demand of distributed optical fiber vibration sensing technology in the above safety monitoring field.Considering the key problems of asymmetric dual Mach-Zehnder interference distributed vibration sensing technology,from the angle of signal processing fusion and multi-sensor mechanism fusion,new methods to improve its vibration sensing performance are proposed.And do the relevant research work in the theoretical framework,system construction,experimental verification,field application and other aspects.The main innovative work of this paper is as follows:1.Constructing the coherent theoretical model of asymmetric dual Mach-Zehnder interference structure.Studying the filtering principle of backscattering noise,the basic principle of vibration detection and the principle of position demodulation.Based on the theory of cross-correlation time delay estimation,the influence mechanism of the asymmetry of vibration signal caused by the difference of laser wavelength on the event location is analyzed.The idea of using the phase change feature to replace the interference signal for positioning is proposed,which lays a theoretical foundation for the research of positioning algorithm.2.For the requirement of accurate detection of vibration starting point,a high-precision end point detection method based on variable mode decomposition is proposed,which improves the detection accuracy by nearly two orders of magnitude compared with the traditional method.A high-precision positioning algorithm based on S-transform and a fast positioning algorithm based on improved 3×3 coupler demodulation are proposed.By extracting the phase change features of two interference signals,the influence of asymmetry of long arm interference structure on positioning accuracy is effectively eliminated.Simultaneously,according to the application requirements of the actual security monitoring,an event recognition mechanism based on probability analysis is proposed.The shortcomings of the existing hard decision output recognition methods are made up,and the loss caused by wrong decision-making is reduced.3.From the perspective of multi-sensor mechanism fusion,a distributed vibration measurement structure merging Mach-Zehnder interference and ?-OTDR is proposed.The structure can realize multi-points positioning and wide-frequency response distributed vibration measurement at the same time,which breaks through the problem that asymmetric dual Mach-Zehnder interference distributed vibration sensing technology cannot achieve multi-points positioning.The influence mechanism of the initial phase difference and vibration amplitude on the frequency detection of the merged system is studied.Based on the improved 3×3 coupler demodulation method,the relative phase difference is calculated.To increase the dynamic range of the system,the relative phase difference is used to replace the interference signal to detect the frequency.A single end single fiber sensing structure is proposed,which combines the feedback loop interference and ?-OTDR.The distributed vibration measurement of multi-point positioning and broadband response is realized on a single fiber at the same time.4.The merged system of Mach-Zehnder interference and ?-OTDR is designed based on the modularization design idea,and the engineering prototype is completed.The linkage alarm communication module with the video monitoring platform and the audible and visual alarm is developed.This communication module not only provides the format output of UDP protocol,but also provides the switch output.Based on the system,the field application experiment is carried out.