| dc.description.abstract |
Nonlinear dynamics of laser systems has become an interesting area of research in recent
times. Lasers are good examples of nonlinear dissipative systems showing many kinds of
nonlinear phenomena such as chaos, multistability and quasiperiodicity. The study of these
phenomena in lasers has fundamental scientific importance since the investigations on these
effects reveal many interesting features of nonlinear effects in practical systems. Further,
the understanding of the instabilities in lasers is helpful in detecting and controlling such
effects.
Chaos is one of the most interesting phenomena shown by nonlinear deterministic systems.
It is found that, like many nonlinear dissipative systems, lasers also show chaos for
certain ranges of parameters. Many investigations on laser chaos have been done in the last
two decades. The earlier studies in this field were concentrated on the dynamical aspects
of laser chaos. However, recent developments in this area mainly belong to the control
and synchronization of chaos. A number of attempts have been reported in controlling
or suppressing chaos in lasers since lasers are the practical systems aimed to operated in
stable or periodic mode. On the other hand, laser chaos has been found to be applicable in
high speed secure communication based on synchronization of chaos. Thus, chaos in laser
systems has technological importance also.
Semiconductor lasers are most applicable in the fields of optical communications among
various kinds of laser due to many reasons such as their compactness, reliability modest cost
and the opportunity of direct current modulation. They show chaos and other instabilities
under various physical conditions such as direct modulation and optical or optoelectronic
feedback. It is desirable for semiconductor lasers to have stable and regular operation.
Thus, the understanding of chaos and other instabilities in semiconductor lasers and their
xi
control is highly important in photonics.
We address the problem of controlling chaos produced by direct modulation of laser
diodes. We consider the delay feedback control methods for this purpose and study their
performance using numerical simulation. Besides the control of chaos, control of other
nonlinear effects such as quasiperiodicity and bistability using delay feedback methods are
also investigated.
A number of secure communication schemes based on synchronization of chaos semiconductor
lasers have been successfully demonstrated theoretically and experimentally. The
current investigations in these field include the study of practical issues on the implementations
of such encryption schemes. We theoretically study the issues such as channel delay,
phase mismatch and frequency detuning on the synchronization of chaos in directly modulated
laser diodes. It would be helpful for designing and implementing chaotic encryption
schemes using synchronization of chaos in modulated semiconductor laser |
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