G. Tissoni

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.

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 Semiconductor Devices

Cavity solitons represent a class of dissipative solitons which are generated inside an optical resonator. They have attracted considerable interest in the recent years due to their possible application to optical information processing. First of all, this review chapter illustrates the physics of cavity solitons in semiconductor devices. We discuss the experiments which demonstrated cavity solitons in vertical-cavity surface-emitting lasers, both below and above threshold, and all the theory which accompanied such experiments. Those features of the experimental results, which relate to prospective applications, are highlighted. The final part of the chapter deals with the theory of the cavity soliton laser.

Phase solitons and domain dynamics in an optically injected semiconductor laser

We analyze experimentally and theoretically the spatio-temporal dynamics of a highly multimode semiconductor laser with coherent optical injection. Due to the particular geometry of the device (a 1~m long ring cavity), the multimode dynamics can be resolved in real time and we observe stable chiral solitons and domain dynamics. The experiment is analyzed in the framework of a set of effective semiconductor Maxwell-Bloch equations. We analyze the stability of stationary solutions and simulate both the complete model and a reduced rate equation model. This allows us to predict domain shrinking and the stability of only one chiral charge that we ascribe to the finite active medium response time.

Thermal and electronic nonlinearities in semiconductor cavities

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.

Control of excitable pulses in a laser with optical injection

We experimentally study the dynamics of a Vertical Cavity-Surface Emitting Laser (VCSEL) with an injected signal subject to an external perturbation, in excitable regime. The possibility to control the kind of response of the system, depending on the perturbation amplitude, is demonstrated. Our perturbation technique induces excitable pulse with 100% efficiency when perturbation is above threshold.

Cavity solitons in driven VCSELS above threshold

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 unstable background.

Interplay of external gradients and material defects in the dynamics of semiconductor cavity solitons

Cavity solitons (CSs) 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 CSs on and off and to control their location and motion makes them interesting as potential pixels for reconfigurable arrays or all-optical processing units.

Slow light and all-optical delay lines using cavity solitons in semiconductor lasers

An all-optical delay line that is based on injecting an optical bit stream into an optical resonator, creating cavity solitons (CS) that drift transversely with a controllable velocity, is proposed and demonstrated. An optical injection experiment is performed in a broad area vertical cavity surface emitting laser emitting at 980 nm.

Cavity solitons in semiconductor microcavities

This work demonstrates unequivocally the existence of cavity solitons (CSs) in semiconductor optical cavity. This study shows that CSs can be written, erased and manipulated as objects independent of each other and of the boundary.