Theoretical And Experimental Study Of Fiber Grating Temperature/Strain Senseing

The research project originates from "bidirectional array fiber Bragg grating composite sensing technology"(BY2015070-01),which is a prospective research project of the joint innovation fund in Jiangsu Province,and it is also a cooperation project between Southeast University and Jiangsu Junzhi Photoelectric Communication incorporated company.The purpose of this thesis is to make theoretical and experimental research on FBG temperature and strain sensing technology,in order to engrave the FBG composite sensor,and form the FBG sensing system used in the optical fiber composite cable.In this thesis,starting from the coupled mode theory,the sensing mechanism of FBG is analyzed and a theoretical and numerical analysis model is established.By the Matlab software,the single mode uniform FBG simulation program is programmed.The effect of the period,length and the effective refractive index modulation depth on the reflection spectrum,transmission spectrum,time delay spectrum and bandwidth of FBG is studied by the control variable method.The characteristics of the bandwidth of the FBG main lobe and the zero point bandwidth of the sidelobe and the time delay characteristics are studied.At the same time,the simulation program of the non-uniform FBG transfer matrix method is compiled,and the performances of chirped FBG and tilted FBG are discussed respectively.On this basis,the temperature and strain sensing mechanism of FBG were studied,and the FBG sensing model was established.The causes and solutions of temperature/strain cross sensitivity of FBG were discussed.Then,a temperature/strain composite sensing scheme based on the center wavelength shift of FBG reflection spectrum and the max delay is proposed.The corresponding analysis model is established and the Matlab simulation program is compiled.The feasibility of the temperature/strain composite sensing scheme is verified by simulation.Based on the program compiled by Matlab,the temperature/strain composite sensing scheme is optimized.The influence of FBG parameters on sensing sensitivity is studied.Finally,the writing platform of fiber Bragg grating phase mask is built in the laboratory.The working principle and main performance parameters of the 248 nm KrF excimer laser,the components of the optical fiber Bragg grating and the corresponding working principle are introduced in detail.The fabrication process of fiber Bragg grating is studied and the uniform,chirped and tilted FBG are fabricated experimentally.The effects of pulse energy,pulse frequency and preset strain on the spectra of FBG were investigated,and the effects of annealing treatment and temperature/strain on the FBG spectra were investigated.