69 research outputs found
Impact of feedback time-distribution on laser dynamics
Time-distributed optical feedback in semiconductor lasers has gained
attention for its ability to produce high-quality chaos and effectively
suppress the time-delay signature. However, the fundamental impact of the
distribution of feedback in time on laser dynamics remains unexplored. In this
paper, we investigate this topic by using fiber Bragg grating (FBG) feedback.
We theoretically study the laser response using FBGs of different lengths but
similar reflectivity, effectively stretching the impulse response over a longer
period while maintaining its overall shape. We observe that above a critical
value corresponding to a grating length of approximately \,cm, fluctuations
in laser stability emerge. We attribute this phenomenon to the damping of
relaxation oscillations when the zeros of the FBG reflectivity spectrum align
with the laser side lobes around the relaxation oscillation frequency. We also
uncover an asymmetrical dynamical behavior of the laser for positive and
negative frequency detuning. We deduce that this asymmetry is a characteristic
feature of FBG feedback and delve into the specificities that trigger such
behavior.Comment: 11 pages, 13 figures, submitte
Optimizing Chaotic Dynamics in a Semiconductor Laser with Dual Optical Feedback
Semiconductor lasers subject to optical feedback can behave chaotically,
which can be used as a source of randomness. The optical feedback, provided by
mirrors at a distance, determines the characteristics of the chaos and thus the
quality of the randomness. However, this fixed distance also shows itself in
the intensity, an unwanted feature called the Time Delay Signature (TDS). One
promising solution to optimize the chaotic behavior is using double optical
feedback, which we study here. In particular, we focus on the impact of the
feedback phase, a small sub-wavelength change in the position of the mirrors,
on the TDS and complexity of the system. We show that by optimizing the
feedback parameters, including the feedback phases, the TDS can be suppressed,
and that in some cases feedback phase control is necessary rather than
optional. With control of all feedback parameters, it is possible to suppress
the TDS without loss of the chaotic bandwidth. Further, we show that the system
can restabilize at strong feedback rates, and one can switch between a chaotic
and steady state by changing the feedback phase. Finally, we relate the
feedback phase sensitivity to interference between the two delayed signals.
This system is promising as one can either suppress the TDS without loss of the
chaotic bandwidth or significantly increase the chaotic bandwidth.Comment: 9 pages, 7 figures, submitte
Deterministic polarization chaos from a laser diode
Fifty years after the invention of the laser diode and fourty years after the
report of the butterfly effect - i.e. the unpredictability of deterministic
chaos, it is said that a laser diode behaves like a damped nonlinear
oscillator. Hence no chaos can be generated unless with additional forcing or
parameter modulation. Here we report the first counter-example of a
free-running laser diode generating chaos. The underlying physics is a
nonlinear coupling between two elliptically polarized modes in a
vertical-cavity surface-emitting laser. We identify chaos in experimental
time-series and show theoretically the bifurcations leading to single- and
double-scroll attractors with characteristics similar to Lorenz chaos. The
reported polarization chaos resembles at first sight a noise-driven mode
hopping but shows opposite statistical properties. Our findings open up new
research areas that combine the high speed performances of microcavity lasers
with controllable and integrated sources of optical chaos.Comment: 13 pages, 5 figure
Vector cavity solitons in broad area Vertical-Cavity Surface-Emitting lasers
We report the experimental observation of two-dimensional vector cavity solitons in a Vertical-Cavity Surface-Emitting Laser (VCSEL) under linearly polarized optical injection when varying optical injection linear polarization direction. The polarization of the cavity soliton is not the one of the optical injection as it acquires a distinct ellipticity. These experimental results are qualitatively reproduced by the spin-flip VCSEL model. Our findings open the road to polarization multiplexing when using cavity solitons in broad-area lasers as pixels in information technology
Dynamique non-linéaire et propriétés de polarisation de diodes lasers nanostructurées
In this thesis, I study the nonlinear dynamics induced by the competition between two modes in quantum dot laser systems.First, I focus on the competition between polarization modes that takes place in quantum dot vertical-cavity surface-emitting lasers (VCSELs). It is well-known that these devices can exhibit polarization instabilities leading to rich dynamical evolution. Recently, a new peculiar random-like hopping between two non-orthogonal elliptically polarized states has been highlighted in QD VCSELs. This behavior shows intriguing features which clearly call for a different interpretation. In this thesis, I show that the dynamical behavior reported experimentally can accurately be reproduced within the spin-flip model (SFM) framework. In particular, I demonstrate and confirm experimentally that the peculiar random-like hoppings are in fact deterministic low-dimensional chaotic fluctuations, i.e. ``Polarization Chaos''. I then make a proof-of-concept demonstration of a high-speed random bit generator based on polarization chaos, hence demonstrating that the chaotic dynamics uncovered is relevant for optical chaos-based applications.Secondly, I investigate the effects of an external optical feedback on quantum dot lasers emitting simultaneously from the ground and the excited states. I bring new light on the impact of optical feedback and the corresponding mechanisms and bifurcations. I highlight theoretically that optical feedback globally favors the ground state emission, but also that it can be used to switch from one mode to the other when changing the feedback rate and/or the time-delay. In addition, I experimentally report switching between the ground and excited states when varying the external cavity length at the micrometer scale, which supports the theoretical predictions.Dans cette thèse, j'étudie la dynamique non linéaire résultant d’une compétition entre deux modes dans des systèmes lasers à boites quantiques.D’abord, je considère le cas de la compétition entre deux modes de polarisation apparaissant dans les diodes laser nanostructurées à cavité verticale et émettant par la surface (VCSELs). Il est connu que ces composants peuvent avoir une polarisation instable menant à des dynamiques riches. Récemment, un surprenant saut de mode entre deux états polarisés elliptiquement a été récemment découvert dans les VCSELs à boites quantiques. Ce comportement montre des propriétés intrigantes qui nécessitent une interprétation alternative. Dans cette thèse, je montre que ce comportement dynamique peut-être reproduit en utilisant le modèle spin-flip (SFM). En particulier je démontre et confirme expérimentalement que les sauts de modes sont en réalité des fluctuations chaotiques de faible dimension : un chaos en polarisation. Je démontre ensuite la pertinence de la dynamique chaotique observée pour les applications exploitant le chaos optique, en réalisant un générateur de nombres aléatoires à grande vitesse basé sur le chaos en polarisation.Deuxièmement, j'étudie les effet d'une rétroaction optique à délai sur les lasers à boites quantiques émettant simultanément depuis l'état fondamental et le premier état excité. Je clarifie l'impact the cette rétroaction optique ainsi que les mécanismes et bifurcations correspondantes. Je montre théoriquement qu'une rétroaction optique favorise globalement l'émission par l'état fondamental, mais aussi qu'un tel montage peut être utilisé pour commuter entre ces deux modes d'émission lorsque l'on change le taux ou le délai de la rétroaction. Enfin, je confirme ces observations expérimentalement, en rapportant des commutations entre l'état fondamental et l'état excité
Multi-dimensional parameter space exploration: the case of chaos in solarity VCSELs
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