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Applications of semiconductor lasers with optical feedback: novel concepts for tunable lasers and chaos control

woensdag, 4 mei, 2011 - 16:00
Campus: Brussels Humanities, Sciences & Engineering campus
K
auditorium P. Janssens
Ilya Ermakov
doctoraatsverdediging

Semiconductor lasers (SLs) are
photonic devices used in many applications
making our life more comfortable.
Technology of manufacturing of SLs
integrated on-chip is developing very
rapidly. Unfortunately, optical feedback
from the other components of the photonic
circuit cannot be always avoided and may
lead to laser in stabilities. Despite many
attempts to understand how feedback
influences behavior of SLs were made, some
aspects are still not clear. Therefore in this
thesis we focus on studying dynamics of SLs
with optical feedback. We use the wellknown
Lang-Kobayashi rate equations that
successfully model dynamics of
semiconductor lasers subject to optical
feedback. The first device studied in the
thesis is a T-shaped Fabry-Pérot SL. We
show numerically that the system, under
certain conditions, is capable of generating a
robust chaotic waveform appropriate for
chaos-based optical communications. Two
such chaotic devices can be synchronized
uni-directionally. The main advantage of our
scheme is short resynchronization time –
time it takes to synchronize the lasers.
Therefore message encryption can be
successfully applied at a rate of hundreds of
Mbit/s.

Another application of a T-shaped SL
can be found in controlling the unstable
emission, like periodic or chaotic oscillations.
Filtered optical feedback is of particular
interest because it allows re-injecting a
specific range of frequencies and efficiently
suppressing arising instabilities. In our
model we use a second feedback branch with
frequency selective mirror to stabilize
periodic or chaotic oscillations induced by
the first conventional branch. We give an
overview of the analytical solution of the
external filtered modes and show
numerically that stabilization when filtered
feedback branch is used is much more
effective compared to conventional feedback.

Semiconductor ring laser is another
interesting device to study optical feedback.
They are promising components in photonic
integrated circuits and can be used for
instance to realize all-optical flip-flops.
However, the potentially detrimental effect
of optical feedback arising from the other
optical components was not investigated yet.
We find theoretically that when crossfeedback
is symmetric the laser works in a
bi-directional continuous wave or periodic
regime for most parameter values. Only for
some small parameter regions we obtain
quasi-periodic behavior and anti-phase
chaos. On the other hand, when the
symmetry is broken complex dynamics such
as quasi-periodicity or chaos emerge.

On-chip filtered optical feedback finds
applications in tunable SLs for selecting the
output wavelength. A novel integrated
tunable laser was proposed and
manufactured at the Technische Universiteit
Eindhoven (TU/e), the Netherlands. Our
numerical simulations show that the
feedback-induced gain competition between
longitudinal modes leads to switching speed
of few nanoseconds. We find theoretically
that the feedback phase is of the great
importance in the tuning process and leads
to direct or inverse switching. For some
values of the feedback phase no switching is
observed.