Bragg gratings in semiconductor waveguides

Master's Thesis from the year 2001 in the subject Electrotechnology, grade: with distinction, City University London, language: English, abstract: Bragg gratings are important devices for both optical communications and

sensing. These devices are used to design very narrow band optical filters, which can

be used in wavelength division multiplexing (WDM). It is also perceived that Bragg

gratings will be used to compensate the dispersion in modern fibre optic

telecommunication networks. Semiconductor gratings are usually integrated into

lasers to control the operating wavelength.

City University Photonic Modelling Group is a world leading research group on

the use of rigorous numerical techniques to design and optimise advanced photonic

devices for optical communications. The research group has already achieved results

on hypothetical one-dimensional (1-D) and realistic two-dimensional (2-D)

structures. In this project a combination of three numerical methods has been used,

all of which are rigorous, to simulate realistic three-dimensional (3-D) structures in

semiconductor waveguides. The combination of these three accurate methods, the

finite element method (FEM), the least squares boundary residual (LSBR) method

and the transfer matrix method (TMM) turned out to be superior to the widely used

coupled mode theory (CMT).

The numerical study of different Bragg gratings shows interesting dependencies

of the characteristics of the gratings on the different design parameters. The work

was carried out for different mesh distributions, different numbers of mesh divisions

and different computational parameters. Another focus of the work was on the

stability of the transmission and reflection coefficients obtained from the LSBR

program. Furthermore the effect of inaccuracy occurring during the fabrication

process has been studied.

The results of this work have been compared to results found by other groups and

fellows. We can say that this project is quite new in the field of reflection spectrum

computation of realistic 3-D semiconductor Bragg gratings. Up to now only a few

papers have been published on such 3-D semiconductor gratings.