Bragg Reflection in Optical Waveguides

Citation

Ouyang, George Xiaoxi (2004) Bragg Reflection in Optical Waveguides. Engineer's thesis, California Institute of Technology. doi:10.7907/31V8-1J13. https://resolver.caltech.edu/CaltechETD:etd-01042005-110346

Abstract

In this dissertation I explore the phenomenon of Bragg reflection in optical waveguides. Two specific waveguide structures are studied in detail: the Bragg fiber and a generic planar waveguide with a Bragg grating etched in it.

Bragg fibers can be classified into two groups: the air-core Bragg fiber and the coaxial Bragg fiber. Whereas the former has a plain air core at the center, the latter contains an additional high-index column in the core. Using a perturbative approach I study and compare the dispersion properties of the two types of fibers, with special attention to their potential for truly single-mode transmission. As the result a large single-mode frequency window, which also includes a zero-dispersion point, is found for the TM mode in the coaxial fiber.

The air-core Bragg fiber is also studied as a potential candidate for dispersion compensation. It is found that Bragg reflections in the fiber are capable of producing negative dispersion values at least as large as -20,000 ps/(nm•km), which is a twenty-fold improvement over previous results. The fiber parameters used for this study are somewhat unrealistic however, and further improvement is necessary before a Bragg fiber can be deployed as a Dispersion Compensating Fiber (DCF).

Optical filters based on Bragg grating structures also involve Bragg reflections. While continuous Fiber Bragg Gratings (FBG's) have long been studied and deployed as practical reflection filters, the possibility of etching a discrete grating in a (planar) waveguide has to my knowledge, never been investigated. In this dissertation I propose a novel scheme for designing such a grating, which is implemented by discretizing its continuous counterpart into a series of air holes. The relationship between the two gratings (discrete and continuous) is established in terms of the grating strength and the local grating period.

Thesis Files