Test And Evaluation Method Of Fiber Bragg Grating Refractive Index Modulation Distribution And Its Applications

With the rapid development of fiber-optic sensing and fiber-communication technology,fiber Bragg gratings(FBGs)have become promising fiber-optic passive devices,which have been used more and more widely.The refractive index modulation(RIM)distribution of FBG determines its spectrum,dispersion and phase-shift characteristics,which have attracted great attention in the fields of dispersion compensation,pulse shaping and fiber laser.White light interference(WLI)is a typical representative of optical fiber technology in cross-domain applications,and has unique advantages in measurement.In this thesis,based on the WLI technology,the test methods of the axial and radial RIM distributions of FBGs are proposed,and test methods related applications are studied.This thesis has mainly completed the following research work:Firstly,the axial FBG RIM distribution test and evaluation method is studied.When the spectra of the FBG and the super-luminescent diode source(SLD)do overlap,the existing traditional discrete layer peeling(TDLP)method is used to simulate and calculate the axial FBG RIM strength.When the spectra of the FBG and the SLD do not overlap,a hardware discrete layer peeling(HDLP)method is proposed and used to evaluate the axial FBG RIM distribution defects.The HDLP method is analyzed by statistical methods,and the relationship between the defect amplitude and the WLI signal intensity is obtained,which can be used to test the axial FBG RIM distribution defect.Secondly,the applications of the axial FBG RIM distribution test and evaluation method are studied.Using the HDLP method,the axial RIM distribution defects of FBGs made by different manufacturers are evaluated.The HDLP method is also applied to study the influence of RIM modulation on the regeneration of FBGs,and the RIM regeneration ratios along an apodized FBG axis before and after regeneration process were measured.The spectral characteristics were used to study the regeneration ratio of the RIM and the fiber refractive index change during the regeneration of the FBG.Then,the radial FBG RIM distribution test and evaluation method is studied.The mode fields of the polarization maintaining fiber(PMF)before and after ultraviolet exposure are simulated to calculate the polarization mode coupling(PMC)strength between the exposed and unexposed PMF contact surfaces and the polarization maintaining fiber Bragg grating(PM-FBG).The measurement of PMC strengths of PM-FBGs is completed by using optical coherent domain polarization(OCDP)measurement technology.When the spectra of the PM-FBG and the SLD do overlap,the envelope appears in the WLI signal.When the spectra of the PM-FBG and the SLD do not overlap,a PMC peak appears at the PM-FBG corresponding position in the WLI signal,and the PMC strength relate to the non uniform radial FBG RIM distribution.Finally,the PMC point induced by PM-FBG with non-uniform radial RIM distribution and its applications are studied.An electric arc based scheme to generate intensity-controllable weak PMC points in PMF is described.Splice and electric arc technology are used to generate PMC points in PMFs,and the performance comparisons are completed in terms of strength controllability,return loss,and mechanical strength.The PM-FBG and its PMCs are used to realize the network measurement of point temperature and area temperature.Using the arc discharge technology,three PMC points with similar PMC strengths are fabricated in a piece of PMF to realize quasi-distributed temperature measurement.