We illustrate the study of extreme events in the spatial transverse section of the electric field emitted by a broadarea semiconductor laser with saturable absorber. Spatiotemporal maxima of the field intensity in the threedimensional space (x, y, t) are identified as events for the statistical analysis. We clearly determine the regions of the parameter space where extreme events are most likely to occur. Furthermore the connection between extreme events and stationary and self-pulsing cavity solitons, occurring in the same system, is investigated.
Cavity solitons are stationary self-organized bright intensity peaks which form over a homogeneous background in the section of broad area radiation beams. They are generated by shining a writing/erasing laser pulse into a nonlinear optical cavity, driven by a holding beam. The ability to control their location and their motion by introducing phase or amplitude gradients in the holding beam makes them interesting as mobile pixels for all-optical processing units. We show the generation of a number of cavity solitons in broad area vertical cavity semiconductor microresonators electrically pumped above transparency but slightly below threshold. The observed spots can be written, erased and manipulated as independent objects. We analyze experimentally the cavity solitons domain of existence in the parameter space and how their characteristics are affected by inhomogeneities and impurities of the vertical cavity devices. A theoretical model, keeping into account the devices characteristics, reproduces numerically the experimental observations with good agreement.
CSs have been theoretically predicted and recently experimentally
demonstrated in broad area, vertical cavity, driven semiconductor
lasers (VCSELs) slightly below the lasing threshold. Above
threshold, the simple adiabatic elimination of the polarization
variable is not correct, leading to oscillatory instabilities with
a spuriously high critical wave-number. To achieve real insight on
the complete dynamical problem, we study here the complete system
of equations and find regimes where a Hopf instability, typical of
lasers above threshold, affects the lower intensity branch of the
homogeneous steady state, while the higher intensity branch is
unstable due to a Turing instability. Numerical results obtained
by direct integration of the dynamical equations show that
writable/erasable CSs are possible in this regime, sitting on
Cavity solitons (CS) appear as self-confined light peaks embedded in the transverse profile of a homogeneous coherent field propagating in a nonlinear cavity. They have recently been predicted for GaAs semiconductor micro cavities for which we have developed a microscopic model that describes the field and the carrier dynamics inside the active region. Here we improve our previous model by adding the temperature dynamics. A detailed study of the instabilities affecting the homogeneous stationary state of the output field is performed. In this way we can address the numerical research of patterns and CS. We then show how it is possible to study intrinsic stability properties of CS by means of semi- analytical techniques that allow to describe the destabilizing mechanisms for solitons, mutual interaction properties and their response to perturbations; possible conceptual schemes for optical information treatment and logic gates are investigated.
We study the formation of self organized light peaks, in GaAs microcavities. By means of analytical and numerical techniques, experimentally accessible parametric domains can be found, where stable and robust CS can be addressed, shifted and brought to interaction ranges, thus realizing some basic schemes for optical information treatment. A Fourier-Newton approach is applied to gain quantitative information on CS's dynamical response to external control fields or on CS pair interaction.
The dead-space carrier multiplication theory properly predicts the reduction in the excess noise factor in a number of APDs. The theory is applied to measurements, obtained from J. C. Campbell and collaborators at the University of Texas, for InP, InAlAs, GaAs, and AlGaAs APDs with multiplication-region widths ranging from 80 nm to 1600 nm. A refined model for the ionization coefficients is reported that is independent of the width of the device multiplication region of each device. In addition, in comparison to predictions from the conventional multiplication theory, the dead-space multiplication theory predicts a reduction in the mean bandwidth as well as a reduction in the power spectral density of the impulse response. In particular, it is shown that the avalanching noise at high-frequencies is reduced as a result of the reduction of the multiplication region width.
Cavity solitons appear as bright spots in the transverse intensity profile. They are similar to spatial solitons, but arise in dissipative systems. Here we consider a broad area vertical cavity resonator, driven by an external coherent field, at room temperature. The active material is constituted either by bulk GaAs, or by a Multiple Quantum Well GaAs/AlGaAs structure (MQW). A general model valid for both configurations is presented and a set of nonlinear dynamical equations is derived. The linear stability analysis of the homogeneous steady states is performed in a general form, holding for the two cases. Then, the nonlinear susceptibilities are specified: in the bulk case, we basically work in the free-carrier approximation, with some phenomenological corrections, such as the Urbach tail and the band-gap renormalization. For the bulk case, some numerical results concerning spatial pattern formation and cavity solitons are given. In the MQW case, on the contrary, we derive a full many-body theory, with the Coulomb enhancement treated in the Pade approximation.
Switching between linearly polarized states of slightly different optical frequencies is found in the fundamental transverse mode pattern is described as the injection current is increased. Polarization switchings obtained here as the injection current is increased in a semiconductor rate equation model incorporating a vector electric field, birefringence and the linewidth enhancement factor, are similar to previously reported experimental results for the fundamental mode. Polarization properties of higher order Gauss-Hermite modes are also analyzed.