Research On Key Technologies Of Distributed Optical Fiber Sensor Signal Processing

With the rapid development of optical fiber communication technology,distributed optical fiber sensor is widely used in the perimeter security of the infrastructure construction of petroleum engineering,natural gas pipeline,communication cable,high-voltage power grid and living quarters for its high sensitivity and wide monitoring range.Distributed optical fiber sensor system mainly consists of optical system and signal processing system,the optical system used to pick up the external interference signal,and the signal processing system used to analyse and process signals.The the signal processing system is very important.It is the key to locate the external disturbance events in real time.The signal processing system with excellent performance can largely make up for many shortcomings in the optical system.Therefore,this paper studies the signal processing technology of distributed optical fiber sensor.Firstly,the phase modulation principle and signal interference principle of optical fiber sensing system are introduced.An interference-type distributed optical fiber sensing structure composed of Mach-Zehnder and Sagnac hybrid interferometer is proposed.Based on the above sensing structure,the phase demodulation technique and vibration localization algorithm of distributed optical fiber sensor are studied.According to the analysis of the transmission characteristics of 3 x 3 coupler,a 3 x 3 coupler demodulation technique based on the least-squares ellipse fitting algorithm is proposed,and the simulation of the sinusoidal interference signal with a single frequency proves the effectiveness of the demodulation method.In order to solve the problem of vibration location,the method of spectrum analysis to find the frequency notch points is proposed.The Welch spectrum estimation is used for spectrum analysis,and the data "clipping method" is used to find the frequency notch points.Secondly,in order to further improve the positioning accuracy of the system,the polarization characteristics and noise characteristics are studied and analyzed,based on the Jones matrix analysis of the influence of light polarization on the interference fringes of the system,to maintain the polarization state of the optical path,the method of setting up the interference module with the Faraday rotating mirror instead of the traditional reflection element and the polarization maintaining device is proposed.At the same time,the characteristics of parasitic interference noise in the interference signals of optical fiber sensing system and its influence on the system are analyzed in detail.A noise reduction method combining adaptive de-noising based on phase carrier technology and morphological filtering is proposed.Finally,according to the above analysis,the specific scheme of the signal processing of the interferometric fiber sensing system is designed.Based on the mixed programming of LabVIEW and MATLAB,the data acquisition module,the noise reduction processing module,the signal demodulation module and the positioning calculation module in the signal processing of the interference type optical fiber sensing system are completed.