Nandakumaran, V M; Bindu M, Krishna; Manu P, John(Cochin University of Science & Technology, 2004)
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Abstract:
Chaotic dynamics of directly modulated semiconductor lasers have been
studied extensively over the last two decades because of their application in secure
optical communication. However, chaos is generally suppressed in such systems when
the nonlinear gain reduction factor is above 0.01 which is very much smaller than
the reported values in semiconductors like InGaAsP. In this paper we show that by
giving an optoelectronic feedback with appropriate delay one can increase the range
of the values of the gain reduction factor for which chaos can be observed. Numerical
studies show that negative feedback is more efficient in producing chaotic dynamics.
Harikrishnan, K P; Dr.Nandakumaran,V M(Cochin University Of Science And Technology, November 3, 1989)
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Abstract:
Nature is full of phenomena which we call
"chaotic", the weather being a prime example.
What we mean by this is that we cannot predict it
to any significant accuracy, either because the
system is inherently complex, or because some of
the governing factors are not deterministic. However,
during recent years it has become clear that
random behaviour can occur even in very simple
systems with very few number of degrees of freedom,
without any need for complexity or indeterminacy.
The discovery that chaos can be generated even with
the help of systems having completely deterministic
rules - often models of natural phenomena - has
stimulated a lo; of research interest recently. Not
that this chaos has no underlying order, but it is
of a subtle kind, that has taken a great deal of
ingenuity to unravel. In the present thesis, the author
introduce a new nonlinear model, a ‘modulated’
logistic map, and analyse it from the view point of
‘deterministic chaos‘.
Description:
Department of Physics, Cochin University of
Science and Technology
Sudheer, Sebastian K(Cochin University of Science and Technology, June , 2010)
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Abstract:
FPS is a more general form of synchronization. Hyperchaotic systems possessing
more than one positive Lypaunov exponent exhibit highly complex behaviour and
are more suitable for some applications like secure communications. In this thesis
we report studies of FPS and MFPS of a few chaotic and hyperchaotic systems.
When all the parameters of the system are known we show that active nonlinear
control method can be efectively used to obtain FPS. Adaptive nonlinear control
and OPCL control method are employed for obtaining FPS and MFPS when some or
all parameters of the system are uncertain. A secure communication scheme based
on MFPS is also proposed in theory. All our theoretical calculations are verified by
numerical simulations.
Description:
Department of Physics,
Cochin University of Science and Technology