Processing of information with optical spikes could present an alternative path with a reduced energy consumption. It could also be well suited in the framework of novel brain-inspired computation paradigms. We investigate the spiking and pulse train dynamics in a micropillar laser with integrated saturable absorber. The optically-pumped microcavity laser is based on a specifically optimized design. The solitary laser can emit sub-nanosecond Q-switched pulses above laser threshold. Below threshold, the laser is in the so-called excitable regime, a generic all-or-none kind of response also found in biological neurons. We demonstrate several neuromimetic properties of the micropillar laser including the relative and absolute refractory periods and the temporal summation. The latter gives rise to sensitive and fast coincidence detectors of optical signals.
In the configuration with delayed optical feedback, the system is shown experimentally and theoretically to sustain controllable trains of dissipative temporal solitons controlled by adequate optical perturbations. We show that the pulse train can be started or resynchronized (retiming) with a single perturbation and that the system can store a large variety of temporal pulse patterns. We discuss the role of pump noise that may terminate a pulse train. We demonstrate a strong asymmetry in the effect of noise on the switch on and off processes, as well as a peculiar role played by noise timing. Besides its interest as a compact source of controllable pulses, this system can be arranged if needed in arrays leading to interesting prospects for artificial optical neural networks.
Recent experiments with an excitable VCSEL micropillar laser with delayed optical feedback demonstrated that the system is able to sustain trains of optical pulses. The laser has two layers of gain and one layer of absorption in the VCSEL cavity, and it is an excitable single longitudinal and transverse mode laser. With optical feedback, a past pulse can trigger a new pulse, creating a pulse train with repetition rate given by the delay time. It is possible to trigger and retime pulses by appropriate external perturbations, in the form of appropriately timed short optical pulses. In particular, several pulse trains can be triggered independently by optical perturbations, and sustained simultaneously in the external cavity, with different timing in between pulses. Such dynamics are also called localised structures, and are investigated here theoretically.
It has been verified experimentally and theoretically that the phase of the electric field is not relevant. The Yamada model – a well-established system of ordinary differential equations for intensity, gain and absorption – is thus a suitable model. As we show, the Yamada model with delayed intensity feedback describes the pulsing micropillar laser system in good agreement with the experiment.
A bifurcation analysis of this model shows that several pulsing periodic solution with different repetition rates coexist and are stable. Although coexisting pulse trains can seem independent on the timescale of the experiment, we show that they correspond here to extremely long transient dynamics toward one of the stable periodic solutions, with equidistant pulses.
Extreme events are characterized by rare and high amplitude excursions of a given variable characterizing a physical system with respect to its long time average. Its study in optics has been primarily motivated by the analogy with rogue waves in hydrodynamics and includes ingredients such as spatial instabilities, nonlinearities and noise.
Here we consider a spatially extended microcavity laser with integrated saturable absorber in the self-pulsing regime. This system, thanks to its short typical timescales, allows large recordings and accurate statistics. Moreover, it does not display irregular or aperiodic dynamics without spatial coupling. Hence, the role of spatial coupling in the emergence of extreme events can be studied. With the help of a model and of numerical analysis together with the experimental observations, we unveil the dynamical origin of the extreme events in the occurrence of spatiotemporal chaos , rather than through collisions of coherent structures. Moreover, by investigating the fine structure of the maximum Lyapunov exponent, of the Lyapunov spectrum and of the Kaplan-Yorke dimension of the chaotic attractor, we are able to deduce that intermittency plays a key role in the proportion of extreme events measured. We assign the observed mechanism of generation of extreme events to quasi-periodic extended spatiotemporal intermittency . The understanding of the formation mechanism of these extreme phenomena is an important step to devise strategies to control them.
 Selmi et al, Phy. Rev. Lett. 116, 013901 (2016).
 Coulibaly et al, Phys. Rev. A 95, 023816 (2017).
We study the nonlinear dynamics of semiconductor micropillar lasers with intracavity saturable absorber in the excitable regime. The excitable regime is characterized by an all-or-none type of response to an input perturbation: when the perturbation amplitude is below the excitable threshold, the system remains in its quiet, stable state; when the perturbation exceeds the excitable threshold, a calibrated response pulse is emitted. It is believed to have great potential for fast neuromorphic optical processing, in addition to being also interesting for the study of nonlinear wave propagation. Fast excitable, neuron-like, dynamics is experimentally evidenced with response times in the 200ps range. We also show the presence of an absolute and a relative refractory periods in this system, analog to what is found in biological neurons but with several orders of magnitude faster response times. The absolute refractory period is the amount of time after a first excitable pulse has been emitted during which it is not possible to excite the system anymore. The relative refractory period is the time after a first excitable pulse during which an inhibited response is emitted and has been often overlooked in optical systems. Both these times are of fundamental importance regarding the propagation of stable excitable waves, and in view of designing spike-time based optical signal processing systems. The experimental results are well described qualitatively by a simple model of a laser with saturable absorber.