Testing Critical Slowing Down as a Bifurcation Indicator in a Low-Dissipation Dynamical System.

We study a two-dimensional low-dissipation nonautonomous dynamical system, with a control parameter that is swept linearly in time across a transcritical bifurcation. We investigate the relaxation time of a perturbation applied to a variable of the system and we show that critical slowing down may occur at a parameter value well above the bifurcation point. We test experimentally the occurrence of critical slowing down by applying a perturbation to the accessible control parameter and we find that this perturbation leaves the system behavior unaltered, thus providing no useful information on the occurrence of critical slowing down.

Extreme events and crises observed in an all-solid-state laser with modulation of losses.

We report observations of extreme events (or dissipative optical rogue waves) in a laser with a modulated parameter (cavity losses). Experimental data supporting the hypothesis that these events are related with multi-stability and external crises is presented. It is also shown that the time separation between a pulse and an extreme event can be predicted more accurately than that between pulses of average intensity, in agreement with the theoretical description and opening the road to the prediction and control of extreme optical events.

Extreme events in chaotic lasers with modulated parameter.

We study a theoretical model describing a laser with a modulated parameter, concentrating on the appearance of extreme events, also called optical rogue pulses. It is shown that two conditions are required for the appearance of such events in this type of nonlinear system: the existence of generalized multi-stability and the collisions of chaotic attractors with unstable orbits in external crisis, expanding the attractor to visit new regions in phase space.

Extreme events in the Ti:sapphire laser.

We report experimental and theoretical evidence of the existence of extreme value events in the form of scarce and randomly emerging giant pulses in the femtosecond (self-pulsing or Kerr-lens mode-locked) Ti:sapphire laser. This laser displays complex dynamical behavior, including deterministic chaos, in two different regimes. The extreme value pulses are observed in the chaotic state of only one of these two regimes.

Deterministic optical rogue waves.

Experimental observations of rare giant pulses or rogue waves were done in the output intensity of an optically injected semiconductor laser. The long-tailed probability distribution function of the pulse amplitude displays clear non-Gaussian features that confirm the rogue wave character of the intensity pulsations. Simulations of a simple rate equation model show good qualitative agreement with the experiments and provide a framework for understanding the observed extreme amplitude events as the result of a deterministic nonlinear process.

Bistable and addressable localized vortices in semiconductor lasers.

We demonstrate experimentally that localized emission states in coupled broad-area semiconductor lasers can carry a finite orbital angular momentum. The resulting structures therefore possess the chirality of optical vortices together with the properties of localized structures in dissipative systems, namely, the coexistence with a low intensity homogeneous emission and the mutual independence. These results open the way to the realization of arrays of optically addressable and bistable chiral laser pixels.

Cavity soliton laser based on mutually coupled semiconductor microresonators.

We report on experimental observation of localized structures in two mutually coupled broad-area semiconductor resonators, one of which acts as a saturable absorber. These structures coexist with a dark homogeneous background and they have the same properties as cavity solitons without requiring the presence of a driving beam into the system. They can be switched individually on and off by means of a local addressing beam.

Mechanisms of polarization switching in single-transverse-mode vertical-cavity surface-emitting lasers: thermal shift and nonlinear semiconductor dynamics.

We analyze polarization switching in vertical-cavity surface-emitting lasers, taking into account a proper semiconductor frequency-dependent complex susceptibility and spin-flip processes. Thermal effects are included as a varying detuning, and gain differences arise from birefringence splitting. We find that, for large birefringence, gain differences between the two linearly polarized modes are preponderant, and switching occurs owing to thermal shift.

Spatial structure of broad-area vertical-cavity regenerative amplifiers.

We investigate the spatial structure of broad-area vertical-cavity regenerative amplifiers injected with a homogeneous beam. The emerging patterns have a predominantly sixfold rotational symmetry, verifying the recent prediction of formation of hexagons. The length scale is controllable by means of detuning and follows the prediction for tilted waves.

Multiplicative noise in the longitudinal mode dynamics of a bulk semiconductor laser.

We analyze theoretically and experimentally the influence of current noise on the longitudinal mode hopping dynamics of a bulk semiconductor laser. It is shown that the mean residence times on each mode have different sensitivity to external noise added to the bias current. In particular, an increase of the noise level enhances the residence time on the longitudinal mode that dominates at low current, evidencing the multiplicative nature of the stochastic process.

Optimization of the switch-on and switch-off transition in a commercial laser.

The response of a Class B laser to a rapid change in one of its parameters is known to be accompanied by delay and ringing. It has been theoretically and numerically shown that the transition can be modified by using adequate functional shapes for the control parameter (e.g.

Stochastic resonance in bulk semiconductor lasers.

The stochastic time scale of the mode hopping in a bulk semiconductor laser can be varied maintaining the symmetry of the residence times by a proper tuning of the laser substrate temperature and pumping current. While the addition of external noise to the pumping current affects the symmetry of the mode-hopping process, a sinusoidal modulation does not, providing that the modulation amplitude is below a critical value. In this case, we observe stochastic resonance in the modal intensities of the laser.

Experimental evidence of van der Pol-Fitzhugh-Nagumo dynamics in semiconductor optical amplifiers.

Thermo-optical pulsing in semiconductor amplifiers is experimentally shown to correspond to a very common excitable scenario (the van der Pol-Fitzhugh-Nagumo system). Self-sustained oscillations appear in the sequence predicted by this simple dynamical model as we change either the injection level or the bias current. Periodic modulation of these parameters leads to the characteristic phase-locking structure.

Cavity solitons as pixels in semiconductor microcavities.

Cavity solitons are localized intensity peaks that can form in a homogeneous background of radiation. They are generated by shining laser pulses into optical cavities that contain a nonlinear medium driven by a coherent field (holding beam). The ability to switch cavity solitons on and off and to control their location and motion by applying laser pulses makes them interesting as potential 'pixels' for reconfigurable arrays or all-optical processing units.

Experimental evidence of coherence resonance in an optical system.

Experimental evidence of coherence resonance in an optical system is reported. We show that the regularity of the excitable pulses in the intensity of a laser diode with optical feedback increases when adding noise, up to an optimal value of the noise strength. Both phase and amplitude fluctuations of the pulses play a relevant role in the dynamics of the system.