Research On Fiber Grating Quality Evaluation Based On White Light Interferometry

The refractive index modulation distribution of fiber gratings determines their spectral intensity and phase characteristics,which have attracted widespread attention in the fields of fiber optic communication and fiber optic sensing.The fiber gratings are fabricated with uncertainties that cause some defects in their refractive index modulation distribution,which affects the characteristics of the fiber gratings.In this thesis,the refractive index modulation distribution of fiber gratings is measured based on white light interference technology,the quality evaluation method of fiber gratings are established,and related applications are studied.This thesis has mainly completed the following research work:Firstly,the transmission characteristics and white light interference signal of fiber gratings are studied.The reflection spectra and group delay characteristic of different fiber gratings are simulated and analyzed by using the transfer matrix method,and the effects of different parameters on reflection spectra and group delay of fiber gratings are discussed.The white light interference signal of the fiber gratings is analyzed for both the spectrum of fiber gratings in the resonant region and non-resonant region.Secondly,the quality evaluation method of fiber gratings based on white light interference technology is studied.When the spectrum of fiber gratings in resonant region,the refractive index modulation distribution defects of the fiber gratings are evaluated by using discrete layer stripping algorithm.The white light interference signal of fiber gratings based on resonant region is measured by using optical low coherent reflection technology.The refractive index modulation distribution of fiber gratings is reconstructed by using discrete layer peeling algorithm,and its discrete coefficient is calculated to obtain the jitter amplitude of refractive index modulation.When the spectrum of fiber gratings in non-resonant region,a hardware discrete layer peeling algorithm is proposed and used to evaluate the refractive index modulation distribution defects of the fiber gratings.The white light interference signal of fiber gratings and their pigtail end face based on non-resonant region is measured by using optical low coherent reflection technology.The white light interference signal of fiber gratings is normalized by the interference intensity of pigtail end face,and its average interference intensity is calculated to obtain the jitter amplitude of refractive index modulation.Finally,the application of fiber gratings based on white light interference technology is studied.A method for measuring the strain distribution of fiber gratings is proposed.The defect interference peaks in the white interference signal of fiber grating are analyzed statistically to obtain the strain distribution of fiber gratings.