Distributed Fiber Sensing Of Rayleigh Scattering Multimode Characteristic Information Based On OFDR

Optical frequency domain reflectometry(OFDR)technology is a kind of technology of distributed sensing technology in the sensitive medium is fiber.Multi modal feature information recognition in optical fiber sensing refers to the experience recognition of measurement parameters combined with time domain amplitude,phase,polarization,dispersion and spectrum of acquisition information.The purpose of this paper is to analyze the OFDR distributed sensing parameters in combination with multimodal feature information recognition.The major innovation of this dissertation are as follow: 1.Firstly,the basic principle of optical frequency domain reflectometry is introduced,and the mathematical model of OFDR beat frequency interference signal is deduced theoretically.Based on the generation mechanism of nonlinear noise,two nonlinear phase noise compensation methods are introduced.2.The optimization analysis of Rayleigh scattering spectral drift modal characteristics is mainly introduced.A new method is developed to increase the measurement sensitivity and spatial resolution by adding additional information over sampling.The spatial resolution can be distinguished from the strain of 3?? and 1cm in the case of spatial resolution.It can increase the strain sensitivity from 0.0348 GHz/?? to 0.1389GHz/??.Finally,an OFDR two-dimensional strain sensing system based on Archimedes helix is proposed.3.We propose a simple and effective method to distinguish strain and temperature,that is,using two kinds of optical fibers to measure the backscattering spectrum of Rayleigh backscattering in OFDR.In the experiment,we measured the optical fiber with a spatial resolution of 18 cm and a total length of 50 m.The temperature error was 0.31 degrees centigrade,and the strain error was 7.97 micro strain.4.A long distance distributed fiber-optic disturbance sensing system based on OFDR is proposed,which can locate multiple disturbance events simultaneously by multi Rayleigh scattering characteristics.The proposed method makes use of the combination of multiple features to simultaneously detect multiple disturbance information.