Bragg gratings in semiconductor waveguides (PDF)

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.