Studies on Some Aspects of Light Beam Propagation Through ...

possibllity of observing the spatiotemporal dynamics of the system in real
time. This also reduces the demands on experiment.al equipment where
speed is often a crucial parameter. Another advantage of photorcfractive
pattern formation is that patterns can be observed using optical powers
of tens of mW. In contrast, pattern formation using other nonlinearities
require optical powers of the order of 1 W.
Chapter 5 deals with the study of self-written waveguides. Besides
the usual analytical analysis, basic experiments were done showing the formation
of self-written waveguide in a photopolymer system. Light induced
or self-written waveguide formation is a recognized technology by which
we can form an optical \vaveguide as a result of the self-trapping action of
a laser beam passed through a converging lens or a single mode fiber. We
report the observation of self-writing in a bulk photopolymer (Methylene
Blue sensitized poly (Vinyl Alcohol)j Acrylamide (MI3PVAj Acrylamide)).
We first present the model equation for the beam propagation through the
photopolymer and analyze it using the variational method. A potential
well formulation is developed. The results are further confirmed by doing
experiments.
The formation of a directional coupler in a phot.opolymer system is
studied theoretically in Chapter 6. Directional couplers are the basis
of several guided wave devices and arc mainly used for optical switching
networks. It is a passive device which couples part of the transmission
power by a known amount t.hrough two transmission lines which are very
close to each other such that energy passing through one is coupled to the
other. "Ve propose and study, using the variational approximation as well
as numerical simulation, the evolution of a probe beam through a directional
coupler formed in a photopolymer system. The t.wo waveguides of
the coupler are formed by direct self-writing. The waveguides so formed
are permanent and can be used to guide light. We show that probe beam
launched into one of the core can efficiently couple into the other core and
the efficiency of coupling increases with the reduction of distance between
the two waveguides. The coupler is analy:wd using the variational met.hod
and the results are compared with that from direct numerical simulation.
Both the result.s are comparable. An analytical result describing the behavior
of the coupler was obtained using the Lagrangian formulation. This
result compares well with the results obtained for a st.andard linear directional
coupler. A potential well formulation is also developed which gives
a physical insight into the dynamics of the coupler.
The main results and conclusion of this t.hesis are given in Chapter
7. The future prospects are also presented.
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