J.R. Tredicce

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. Theoretical work on cavity solitons has stimulated a variety of experiments in macroscopic cavities and in systems with optical feedback. But for practical devices, it is desirable to generate cavity solitons in semiconductor structures, which would allow fast response and miniaturization. The existence of cavity solitons in semiconductor microcavities has been predicted theoretically, and precursors of cavity solitons have been observed, but clear experimental realization has been hindered by boundary-dependence of the resulting optical patterns—cavity solitons should be self-confined. Here we demonstrate the generation of cavity solitons in vertical cavity semiconductor microresonators that are electrically pumped above transparency but slightly below lasing threshold. We show that the generated optical spots can be written, erased and manipulated as objects independent of each other and of the boundary. Numerical simulations allow for a clearer interpretation of experimental results.

Instabilities in lasers with an injected signal

We consider a laser with an injected signal, in which the polarization can be adiabatically eliminated, we study the stability of the steady-state solutions, and we discuss the time-dependent solutions. For the laser alone, the only possible solution is constant intensity. However, the introduction of an external field, with an amplitude that does not satisfy the injection-locking condition, destabilizes the system. In such a case, numerical results show the existence of a self-Q-switching process, which induces relaxation oscillations. The frequency of the giant pulses is directly related to the amplitude of the external field, whereas the frequency of the relaxation oscillations depends on the damping rates. We show also that, depending on the value assigned to control parameters, the interaction between these frequencies leads to a chaotic behavior through intermittency or period-doubling bifurcations. Finally, topological equivalence between our laser system and a unidimensional circle map is shown for some values of control parameters.

Calculating the dimension of attractors from small data sets

Abstract Calculations of the order-2 information dimension for data sets generated from numerical simulations as well as from an experiment show that it is possible to distinguish between periodic, chaotic and random signals, as well as to characterize different kinds of chaotic behavior using relatively small, noisy data sets.

Deterministic chaos in laser with injected signal

Abstract Dynamic behaviour of an homogeneously broadened laser with injected signal is analyzed for a model in which the polarization is adiabatically eliminated. Detuning between the atomic resonant frequency, the cavity resonance and the frequency of the external signal is considered. We show that a transition to chaos via intermittency is possible for parameters appropriate for CO2 lasers.

Instabilities and spatial complexity in a laser

We discuss the emergence of spatial structures in a ring laser model with transverse effects. The emphasis of this study is on the development of a description that can capture the essential features of transverse dynamics without the need for large-scale numerical efforts. We introduce an extension of the uniform field limit and derive a set of modal equations that we solve with conventional numerical methods. Our solutions show evidence of transverse mode competition in the laser dynamics, leading to both time-dependent and multimode stationary (cooperative frequency-locking) behaviors. In the time-dependent regime we analyze the resulting spatial structures and suggest a scheme for the investigation and characterization of spatial complexity.

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.

All-optical delay line using semiconductor cavity solitons

An all-optical delay line based on the lateral drift of cavity solitons in semiconductor microresonators is proposed and experimentally demonstrated. The functionalities of the device proposed as well as its performance is analyzed and compared with recent alternative methods based on the decrease of group velocity in the vicinity of resonances. We show that the current limitations can be overcome using broader devices with tailored material responses.

Cavity solitons in a driven VCSEL above threshold

We experimentally demonstrate the existence and the control of cavity solitons in externally driven vertical-cavity semiconductor lasers above threshold. A model including material polarization dynamics is used to predict and confirm the experimental findings.

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. For small birefringence polarization switching from the high- to the low-gain mode occurs owing to the combined effect of birefringence and semiconductor phase-amplitude-coupled dynamics for a finite value of the carrier spin-flip rate.

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. The observations agree with the predictions of a well-tested theoretical model that does not include noise or self-Q-switching into its framework. This implies that, in this laser, the extreme effects have a nontrivial dynamical origin. The Ti:sapphire laser is hence revealed as a new and convenient system for the study of these effects.