The Research On Characteristics Of Bragg Reflector Based On Mode-mathching Method

Optical devices are of vital importance for the construction of optical communication network. It is therefore of great importance to study the characteristics of Bragg reflector, for a lot of optical devices such as wavelength division multiplexor/demultiplexor, VCSEL, distributed feedback laser, wavelength converter, dispersion compensator, are based on it. Fiber Bragg grating and deep-etch Bragg reflector, for example, are two important passive optical elements that follow Bragg reflection principle. Fiber Bragg grating, which is fabricated directly into a fiber by ultraviolet exposure, has the advantage of low insertion loss, insensitivity to polarization and good matching with a fiber. While deep-etch Bragg reflector is able to achieve very high reflection in a compact structure and it's widely used in DFB semiconductor lasers.The thesis composed a program in Matlab language for mode-matching method and analyzed the characteristics of deep-etch Bragg reflector in the rectangular coordinates and Fiber Bragg grating in the cylindrical coordinates separately.First a quick analytical method was presented for the calculation of the reflection spectrum of a deep-etch Bragg reflector. Then the exact optical fields inside a deep-etch Bragg reflector were calculated using mode-matching method when the Bragg reflection condition is and is not satisfied separately.Next, spectrum characteristics of uniform fiber Bragg grating and linearly chirped fiber Bragg grating were investigated. It was find that for both uniform fiber Bragg grating and linearly chirped fiber Bragg grating as their lengths increase, their reflection band become narrower and the reflection rates increase toward one; the central reflection wavelength becomes longer as the period becomes larger; the reflection band becomes wider and the reflection rates decrease as their refraction index modulation increase; and for linearly chirped fiber Bragg grating, the reflection band becomes wider as the chirping value become larger. These principles are very useful for the optimum design of a fiber Bragg grating.