Definition of the stimulated emission threshold in high-β\beta nanoscale lasers through phase-space reconstruction

Nanoscale lasers sustain few optical modes so that the fraction of spontaneous emission $\beta$ funnelled into the useful (lasing) mode is high (of the order of few 10$^{-1}$) and the threshold, which traditionally corresponds to an abrupt kink in the light in- light out curve, becomes ill-defined. We propose an alternative definition of the threshold, based on the dynamical response of the laser, which is valid even for $\beta=1$ lasers. The laser dynamics is analyzed through a reconstruction of its phase-space trajectory for pulsed excitation. Crossing the threshold brings about a change in the shape of the trajectory and in the area contained in it. An unambiguous definition of the threshold in terms of this change is shown theoretically and illustrated experimentally in a photonic crystal laser

Vector cavity solitons in broad area Vertical-Cavity Surface-Emitting lasers

We report the experimental observation of two-dimensional vector cavity solitons in a Vertical-Cavity Surface-Emitting Laser (VCSEL) under linearly polarized optical injection when varying optical injection linear polarization direction. The polarization of the cavity soliton is not the one of the optical injection as it acquires a distinct ellipticity. These experimental results are qualitatively reproduced by the spin-flip VCSEL model. Our findings open the road to polarization multiplexing when using cavity solitons in broad-area lasers as pixels in information technology

Regenerative memory in time-delayed neuromorphic photonic resonators

We investigate a photonic regenerative memory based upon a neuromorphic oscillator with a delayed self-feedback (autaptic) connection. We disclose the existence of a unique temporal response characteristic of localized structures enabling an ideal support for bits in an optical buffer memory for storage and reshaping of data information. We link our experimental implementation, based upon a nanoscale nonlinear resonant tunneling diode driving a laser, to the paradigm of neuronal activity, the FitzHugh-Nagumo model with delayed feedback. This proof-of-concept photonic regenerative memory might constitute a building block for a new class of neuron-inspired photonic memories that can handle high bit-rate optical signals

Cavity solitons in broad-area vertical-cavity surface-emitting lasers below threshold

Massimo Brambilla...et al.-- PACS number(s): 42.65.Sf, 42.70.Nq, 42.65.TCavity 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. We analyze the switching process in details. The observed spots can be written, erased, and manipulated as independent objects, as predicted by the theoretical model. An especially tailored one is used to simulate the studied phenomena and to compare our simulations to the experimental findings with good agreement.The INLN group acknowledges ACI photonique “Contrôle et manipulation de solitons de cavité dans les systèmes optiques auto-organisés.” The groups in Bari and Como acknowledge the PRIN project “Formazione e controllo di solitoni di cavitá in microrisonatori a semiconduttore” of the Italian Ministry of University and Research, and the European Network VISTA (VCSELs for Information Society Technology Applications)Peer reviewe

Impact of Light Polarization and Optical Feedback on Spatially Localized Structures in Vertical-cavity

info:eu-repo/semantics/nonPublishe

Mode-switching in semiconductor lasers

In this paper, we experimentally analyze the modal dynamics of quantum-well semiconductor lasers. Modal switching is the dominant feature for semiconductor lasers that exhibit two or several active longitudinal modes in their time-averaged optical spectrum. In quantum-well lasers, these dynamics involve a periodic switching among several longitudinal modes, which follows a well-determined sequence from the bluest to the reddest mode in the optical spectrum. This feature is radically different from the well-known noise-driven mode-hopping occurring in bulk lasers which involves only two main modes. We analyze the differences in modal dynamics for these two kinds of laser by comparing the modal switching statistics and by studying the effects of noise and modulation in the pumping current. © 2004 IEEE.Peer Reviewe

Modal switching in quantum-well semiconductor lasers with weak optical feedback

We analyze theoretically and experimentally how the modal dynamics of quantum-well semiconductor lasers is affected by weak optical feedback. Without feedback, these lasers exhibit a regular switching among several longitudinal modes, following a well determined modal sequence and leaving the total intensity output constant. Using a multimode theoretical model we have identified the four wave mixing as the dominant mechanism at the origin of these intriguing dynamics, while the asymmetry of the susceptibility function of semiconductor materials allows to explain the modal sequence. In this manuscript we show that these dynamics, which is almost insensitive to current noise or modulation, is instead extremely sensitive to optical feedback. The experimental results are satisfactorily compared with the numerical predictions of the model, properly adapted for including weak optical feedback. © 2005 IEEE.Peer Reviewe

Cavity-solitons switching in semiconductor microcavities

Cavity solitons (CSs) are localized structures appearing as intensity peaks in the homogeneous background of the field emitted by a nonlinear microresonator. We experimentally and theoretically study the switch-on process of cavity solitons in semiconductor amplifiers. The switching time has two contributions: a lethargic lapse following the application of the switching pulse and a characteristic buildup time. While the latter is not significantly affected by the control parameters, the former crucially depends on them. Optimization of the parameters leads to a switch-on time of less than one nanosecond, assessing the CS competitiveness for all-optical applications