Project title (in english):
Physics
of Optoelectronic Oscillator Circuits for Communication Systems
Applications*
Projecto
distinguido pelo Programa Estímulo à Criatividade e à
Qualidade na
Actividade de Investigação da Fundação Calouste Gulbenkian na área
científica
Física dos Sistemas Complexos. Investigador e
instituição distinguidos: Bruno Romeira (CEOT/UALG) e
Departamento de Física da UALG.
Summary
Since the discover, in 1961 by Edward
Lorenz, what
is now known as the butterfly effect, chaos became an essential
research topic
in biological, chemical, physical, and social sciences. With particular
interest is the use of chaotic signals for information transmission.
The use of
the noise-like appearance of chaotic carriers gives a very efficient
way to
mask messages, and is considered a promising method to improve security
in
communications. Communication systems using chaotic optical carriers
allow implementing
steganography techniques at the physical
level, which
improves substantially the security of the software current encryption
techniques. In such systems the receiver circuit, an identical version
of the
transmitter circuit, is synchronized with the chaotic emission to allow
message
decoding.
The most promising ways of producing
broadband
chaotic signals employ semiconductor lasers as sources of chaotic
optical
carriers. Although semiconductor laser systems are, in general,
dynamical
stable, instabilities can be induced by perturbing their operation
either
through direct current modulation, optical injection, optical feedback,
or
delayed optoelectronic feedback. Such perturbations correspond to the
addition
of new degrees of freedom to the systems and are widely proposed as
methods of
broadband chaotic optical signals generation. However,
the
complexity of most of theses systems, either hybrid or monolithic,
makes
practical realization very challenging.
Following
recent
reports on chaotic dynamics in a new type of optoelectronic circuit, we
propose
an alternative laser diode system configuration capable of chaos
generation
based on the integration of a double-barrier quantum well (DBQW)
resonant
tunnelling diode (RTD) with a communications semiconductor laser diode
(LD),
the RTD-LD circuit/system. Such system takes advantage of the
combination of
RTD and LD intrinsic nonlinear dynamics, leading to substantial
reduction of
transmitter and receiver circuits’ complexity and less restrictive
operation conditions. The DBQW-RTD is a nonlinear nanoelectronic device
capable
to operate at room temperature as a high frequency voltage controlled
oscillator (VCO), that shows wideband negative differential resistance
allowing
ultra-broadband electrical gain (currently up to 831 GHz), that when
properly
perturbed shows extremely complex non-linear dynamics.
Here we propose to investigate the
physics of
RTD-LD systems that leads to a rich complex dynamics, including the Feigenbaum, the intermittent and the
quasi-periodic routes
to chaos, which are related to the period doubling, saddle-node, and Hopf bifurcations, respectively. Preliminary
results
indicate this complex system can be an alternative to proposed
optoelectronic
chaotic generator systems. The investigation will comprehend the
physics that
leads to the system nonlinear dynamics and synchronization between two
identical circuits, one acting as transmitter and the other as
receiver.
Since the
RTD-LD
system is completely compatible with current optical communication
systems, and
because the combination of RTD nonlinear characteristics with LD
dynamics
reduces significantly operation conditions constraints of the laser
diode
necessary to produce high-dimensional chaos, it leads to
straightforward chaos
based optical communication systems implementation. The investigation
will also
allow a deeper insight into the theory of a new category of
optoelectronic
complex systems.
Research team
Bruno
Romeira
(CEOT/UALG, DF/UALG)
José
Figueiredo (CEOT/UALG, DF/UALG)
Additional
Research Unit
Department
of Electronics and Electrical Engineering,
Instituto de
Microelectrónica de Sevilla,
IMSE-CNM, Universidad de Sevilla
url: http://w3.ualg.pt/~jlongras/R/RTD-OEC.html