Investigations Of Characteristics And Applications Of Chirped And Phase-shifted Fiber Bragg Gratings

A phase-shifted fiber Bragg grating (PS-FBG) is formed when a phase shift is incorporated in a uniform fiber Bragg grating (FBG) by breaking up the continuity of periodicity of the grating. At present, there has been a significant advance in the investigation of PS-FBGs. However, the investigations focused on non-chirped PS-FBGs. In this paper, we study the characteristics of chirped PS-FBGs. Compared with a non-chirped PS-FBG, in addition to the same characteristics of a non-chirped PS-FBG, both the reflection and transmission windows of a chirped PS-FBG can be broadened in a wider range. The work in this paper can be used to design the new devices based on chirped PS-FBGs.In Chapter 1, the development and fabrication of different types of FBGs have been summarized, followed by a comprehensive introduction to the applications of FBGs in optical communications and sensors.In Chapter 2, the theoretical basis of the dissertation is presented. According to electromagnetic theory of waveguides, the coupled-mode equations for the interactions between the modes are deduced. Furthermore, in order to simulate the characteristics of FBGs, we briefly introduce the Runge-Kutta method, transfer matrix method, algorithm based on Newton-Raphson method and algorithm by Fatemeh Abrishamian, and analyze the applicability of the four algorithms. For different FBGs, we should choose the most convenient and fast algorithm.In Chapter 3, characteristics of chirped PS-FBGs have been investigated by use of transfer matrix method and are compared with those of non-chirped PS-FBGs. Applications of chirped PS-FBGs in narrow linewidth single-frequency lasers, WDM or DWDM optical communication systems and gain flattening of Erbium-doped fibers are discussed.In Chapter 4, the characteristics of chirped PS-FBGs under noise have been investigated. The wavelength tuning principle of fiber Bragg gratings under strain and temperature is introduced. Characteristics of a chirped PS-FBG under strain and temperature have been simulated. The peak wavelength of transmission window has a good linear relationship with strain and temperature, however, the peak reflectivity of transmission window is not sensitive with strain and temperature.