I. M. Perrini

Cavity solitons in passive bulk semiconductor microcavities. I. Microscopic model and modulational instabilities

We consider a broad-area vertical microresonator with an active layer constituted by bulk GaAs driven by an external coherent homogeneous electromagnetic field, and we adopt a microscopic model that describes the field and carrier dynamics in the quasi-equilibrium regime. The theory is developed within the free-carrier approximation, with some relevant effects, such as the Urbach tail and the bandgap renormalization, which are taken into account in a phenomenological way. We include in the model the description of paraxial diffraction and carrier diffusion. A detailed study of the instabilities, both modulational and plane wave, affecting the homogeneous stationary state of the output field is performed. In this way we address the numerical research of cavity solitons, which appear as self-organized light peaks embedded in a homogeneous background, as discussed in a companion paper [J. Opt. Soc. Am. B16, 2095 (1999)]. Optimal conditions for cavity solitons’ existence are found in extended regions of the parameter space.

Cavity solitons in passive bulk semiconductor microcavities. II. Dynamical properties and control

We analyze numerically the microscopic model formulated in a companion paper [J. Opt. Soc. Am. B16, 2083 (1999)] to describe an externally driven broad-area bulk GaAs microcavity. We numerically predict the formation of patterns in the transverse profile of the output field. In particular, we find the existence of stable cavity solitons, which appear as self-organized light peaks embedded in a homogeneous background. We study the characteristics of such structures and specifically the possibility of switching them on and off at desired locations in the transverse field profile. Moreover, we analyze the interaction properties of cavity solitons with the purpose of applying them, in the future, to optical information treatment. Finally, we study the dynamical properties of cavity solitons, quantitatively evaluating the motion across the transverse plane induced by spatial gradients in the input field profile.

Optical patterns and cavity solitons in quantum-dot microresonators

We study optical transverse instabilities in quantum-dot (QD) microresonators. We develop a model for the QD susceptibility taking into account the inhomogeneous broadening of the dot emission. A linear stability analysis and numerical integration of the resulting equations are performed. Special attention is paid to the formation of such structures as optical patterns and cavity solitons, which could play an important role in the field of optical information processing. Implications for actual QD materials are discussed in view of applications.

Spatio-temporal dynamics in semiconductor microresonators with thermal effects

In this paper we study the dynamics of the intracavity field, carriers and lattice temperature in externally driven semiconductor microcavities. The combination/competition of the different time-scales of the dynamical variables together with diffraction and carrier/thermal diffusions are responsible for new dynamical behaviors. We report here the occurrence of a spatio-temporal instability of the Hopf type giving rise to Regenerative Oscillations and travelling patterns and cavity solitons.

Cavity solitons in broad area VCSELs below threshold

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.

Modeling pattern formation and cavity solitons in quantum dot optical microresonators in absorbing and amplifying regimes

We present a complete overview of our investigation past and present of the modelization and study of the spatiotemporal dynamics of a coherent field emitted by a semiconductor microcavity based on self-assembled quantum dots. The modelistic approach is discussed in relation to prospective growth and experimental research, and the model is then applied to resonators for which the medium is either passive (coherent photogeneration of carriers) or active (carrier pumping by current bias). The optical response of the system is investigated, especially in what concerns the linewidth enhancement factor, which turns out to be critical for the onset of self-organized patterns. The regimes in which one can expect bistable response, modulational instabilities, pattern formation, and cavity soliton formation are investigated. The pattern scenario is described, and experimentally achievable conditions are predicted for the occurrence of stable cavity solitons.

Thermal effects and cavity solitons in passive semiconductor microresonators

We formulate a model including the thermal dynamics in the time evolution of a passive semiconductor microresonator, containing a bulk medium, driven by a coherent holding beam. Thermal effects are taken into account via a dynamical equation for the lattice temperature, describing heat dissipation toward the environment, heating due to carrier generation, and thermal diffusion. The temperature dynamics is coupled to the carrier and field dynamics via the material susceptibility, a red-shift of the band-gap energy of the semiconductor upon an increase of temperature and a linear shift of the cavity resonance. The presence of thermal effects introduces a Hopf instability which, in certain regions of the parameter space, dominates the dynamics of the system. In this case our numerical simulations show that the output intensity may oscillate for constant holding beam intensity (regenerative oscillations), and if the input intensity grows slowly enough the hysteresis cycle may be inverted (switching point inversion). Oscillatory instabilities can also develop a modulational character, meaning that travelling patterns can be found. These phenomena develop over the slow timescale (microseconds) characterizing thermal effects in these devices. In other parameter regimes, the well-known Turing instability giving rise to stationary modulated patterns prevails, and the system displays the usual scenario of stable patterns and cavity solitons. Thermal effects seem not to play any relevant role in these regimes.

THE PHYSICS OF CAVITY SOLITONS IN SEMICONDUCTOR MICROCAVITIES

We start by reviewing the basic physical properties of cavity solitons, embedding this phenomenon in the general framework of optical instabilities and optical pattern formation. Next, we focus on the case of semiconductor microcavities and consider a first principle model. Its homogeneous stationary solutions and their stability are evaluated analytically. With the help of numerical simulations, we discuss two case studies, one in the passive and one in the active configuration.

Controlling cavity solitons in semiconductor microcavities for optical information treatment

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 CSs dynamical response to external control fields or on CS pair interaction.

Three-dimensional pattern formation in semiconductor microcavities

We study pattern formation in a paraxial model for an unidirectional ring resonator filled with a semiconductor sample and driven by a coherent injected field beyond the mean field limit (MFL). We perform numerical simulations to describe the three-dimensional dynamics of the coherent field profile. For fast media spontaneous self-confinement leads to the formation of 3D dissipative addressable spatial solitons, we show that for carrier dynamics compatible with GaAs/GaAlAs MQW devices longitudinal self-confinement is hindered by the slow carrier interband dynamics.