Abstract
D.Phil. (Electrical & Electronic Engineering Science)
Recent advancement in optical fibre communications technology is partly due to the
advancement of optical thin-film technology. The advancement of optical thin-film
technology includes the development of new and existing deposition and optical filter
design methods. Genetic algorithm is one of the new design methods that show
promising results in designing a number of complicated design specifications. The
research is entirely devoted to the investigation of the genetic algorithm design
method in the design of producible polarised and non-polarised edge filters for optical
fibre communication applications. In this study, a number of optical filter design
methods such as Fourier Transform and refining are investigated for their potential in
designing those kinds of structures. Owing to the serious limitations to which they are
subject, they could not yield the kind of results anticipated. It is the finding of this
study that the genetic algorithm design method, through its optimisation capability,
can give reliable and producible designs. This design method, in this study, optimises
the thickness of each layer to get to the best possible solution. Its capability and
unavoidable limitations in designing polarised and non-polarised beam splitters, edge
filters and reflectors from absorptive and dispersive materials are well demonstrated.
It is observed that the optical behaviour of the non-polarised filters designed by this
method show a similar trend: as the angle of incidence increases the inevitable
increase in the percentage of polarisation, stop bandwidth and ripple intensity is well
controlled to an acceptable level. In the case of polarised designs the S-polarised
designs show a better response to the optimisation process than the P-polarised
designs, but all of them are kept well within an acceptable level. It is also
demonstrated that polarised and non-polarised designs from the genetic algorithm
are producible with great success. This research has accomplished the task of
formulating a computer program using genetic algorithm in a Mathlab® environment
for the design of producible polarised and non-polarised filters from materials of
absorptive and dispersive nature.