Simulation And Measurement Of Fiber Bragg Gratings

The next generation of high-capacity WDM telecommunication networks demand the high-performance optical devices in routing,filtering,control and amplification of optical signals. The characteristics of photosensitivity technology and its inherent compatibility with optical fiber have enabled the fabrication of a variety of different Bragg grating fiber devices. According to its excellent characteristics in spectral filtering,dispersion compensation,wavelength tuning and sensing, fiber Bragg gratings have became more and more interests.In this dissertation, the reflection characteristics of fiber Bragg grating have been numerically and experimentally studied. The reflection spectrums of few-mode and multi-mode fiber Bragg grating (MM-FBG) with non-uniform profile of index change have been numerically simulated and measured.In the first chapter, the history of FBGs has been briefly reviewed. Backgrounds on FBGs'fabrication, theoretical and experimental studies have been overviewed. The important applications of FBGs in the field of optical communications and sensing have been summarized. In the second chapter, based on electromagnetic wave theory of optical fibers, the mode theory of fiber is introduced. The numerical solution of eigen-values and mode field distribution of step-index optical fiber are discussed. Second, the eigen-functions and mode field distribution of graded-index optical fiber are introduced.In the third chapter, taking the FBG as refractive index perturbation, the coupled-mode equations of MM-FBG are derived from the Maxwell's functions. The model of FBGs for numerical simulation is established, which is the basis of following simulation work.In the fourth chapter, the numerical methods used in the simulation of fiber Bragg grating are developed. In the frame of shooting method, we developed a fast method to numerically solve the coupled-mode equations of MM-FBG using the analytical solution of the initial problem of the coupled mode equations by diagonalization.In the fifth chapter, the reflection spectrums of few-mode fiber Bragg gratings (FM-FBGs) are obtained by solving the coupled mode equations (CMEs) using numerical method developed previously. Considering the impact of photosensitivity on non-uniform profile of index change, the reflection characteristics of linear polarization mode in FM-FBGs are simulated numerically.In the sixth chapter, the reflection characteristics of MM-FBG with the non-uniform profile of index change are analyzed and studied. The impact of the maximum photo-induced index change, saturation length and the distribution of fiber modes on the reflection characteristics are studied.In the seventh chapter, the experimental results of reflection spectrum of MM-FBG with different offsets, index change and grating length are investigated. Combined with the results from simulation, the experimental results are analyzed.In the eighth chapter, the dissertation is summarized.