Inhomogeneous lens stuctures for integrated optics

Finlayson, Neil (1985) Inhomogeneous lens stuctures for integrated optics. PhD thesis, University of Glasgow.

Abstract

The thesis is concerned with the design, analysis,
fabrication am evaluation of integrated optic lenses which are
inhomogeneous either in physical shape or in refractive index
profile. The thesis has nine chapters. Chapter one, the
introduction, illustrates the importance of these lenses within
the domain of integrated optiCS, where the complicated
mathematical functions required to describe the lens profiles are
most easily realised. Connections are made between the study of
these lenses and the exciting new field of optical computing.
A special class of non-uniform lenses which are conceptually
perfect optical instruments forms the main area of interest in
the present study. Historically, the development of these lenses
has followed two distinct lines, related to two possible methods
of physically obtaining the required variation in path of light
rays passing through the lens. In one method the optical path is
made to vary directly, whilst the other method involves
controlling the fi'lysical path, and thus the optical path, through
the principle of equivalence. The dual development has been
continued in the field of integrated optiCS, where lenses based
on direct control of the optical path are termed variable-index
lenses and those based on physical path control are termed
geodesic lenses. The perfect variable-index lens studied in this
work was the well-known Luneburg lens. Perfect geodesic lens
designs have also been published. The design formulae for both
types of lens are presented in chapter two. A simpler lens, of
spherical geometry, is also presented which is easily analyzed
and characterised and which serves as an archetypal model against
which the performance of the more sophisticated lenses can be
assessed.
Chapter three investigates the problems involved in
modelling fabrication conditions in a thermal-evaporation-invacuum
environment so that lens profiles can actually be
constructed. Chapter four goes into methods of tracing rays
through these lenses in some detail. Ray-tracing has long been the classical tool of optical designers, providing a useful guide
to optical performance. Ray methods, which effectively provide
image error evaluations, are not entirely-appropriate for those
lenses which are conceptually perfect within the geometrical
optics approximation. Diffraction effects prevent the lenses from
attaining true perfection. In such cases the wave-field produced
by the lenses in the image space is the important quantity. In
chapter five, the beam-propagation method (BPM) is used to study
diffraction arrl associated effects in inhomogeneous lenses. '!he
method allows the propagation of complicated waveshapes in
lnhomogeneous media, normally a difficult task. Furthermore,
anlsotropic effects and the interaction between acoustic waves
aoo optical waves can be studied with the method. Negative focal
shifts are reported which are not predicted by geometrical optics
or the usual approximate diffraction theories.
The fabrication of lenses is considered in chapter six.
Planar waveguide measurements car r ied out on the var ious
materials used in the study are presented. A major problem in the
fabrication of geodesic lenses, that of obtaining a uniform
wavegulde layer over the complete lens area, is dealt with in
some detail in chapter seven. In chapter eight, extensive tests
on the experimental performance of several lenses are reported.
Near diffraction-limited performance is reported for geodesic
lenses. More limited performance figures are obtained for
Luneburg lenses though the possibility of high performance is
lndicated if profile resolution can be improved. The themes of
the thesls are pulled together for discussion in chapter nine and
conclusions are drawn as to the relative merits of the various
lenses. Possible means of improving fabrication procedures, thus
driving lenses closer to ultimate resolution limits, are
presented. The greatest problem faced is that of scatter ing in
the waveguide, which appears to be accentuated as the waveguide
traverses the lens surface. If the scattering problem can be
successfully dealt with it is concluded that integrated optical
lenses could be important and viable components in addresslng the
problem of fast, high-throughput data processing.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > T Technology (General)
• Colleges/Schools: College of Science and Engineering
• Supervisor's Name: De La Rue, Dr. R.M.
• Date of Award: 1985
• Depositing User: Ms Mary Anne Meyering
• Unique ID: glathesis:1985-4929
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 06 Feb 2014 13:48
• Last Modified: 06 Feb 2014 16:43
• URI: https://theses.gla.ac.uk/id/eprint/4929