Foued Selmi

Spatiotemporal Chaos Induces Extreme Events in an Extended Microcavity Laser

Extreme events such as rogue waves in optics and fluids are often associated with the merging dynamics of coherent structures. We present experimental and numerical results on the physics of extreme event appearance in a spatially extended semiconductor microcavity laser with an intracavity saturable absorber. This system can display deterministic irregular dynamics only, thanks to spatial coupling through diffraction of light. We have identified parameter regions where extreme events are encountered and established the origin of this dynamics in the emergence of deterministic spatiotemporal chaos, through the correspondence between the proportion of extreme events and the dimension of the strange attractor.

Temporal summation in a neuromimetic micropillar laser

Neuromimetic systems are systems mimicking the functionalities or architecture of biological neurons and may present an alternative path for efficient computing and information processing. We demonstrate here experimentally temporal summation in a neuromimetic micropillar laser with an integrated saturable absorber. Temporal summation is the property of neurons to integrate delayed input stimuli and to respond by an all-or-none kind of response if the inputs arrive in a sufficiently small time window. Our system alone may act as a fast optical coincidence detector and paves the way to fast photonic spike-processing networks.

Self-pulsing and fast excitable response in micropillar and nano-lasers with saturable absorber

We present recent experimental and theoretical results on the nonlinear dynamics of semiconductor micro and nano-lasers. First, fast excitable, neuron-like, dynamics is experimentally evidenced in a micropillar laser with intracavity saturable absorber with fast response times in the 200ps range. We study also the refractory time in this system and show the existence of a relative refractory period, analogue to what is found in neurons. Second, we propose a scheme for achieving self-pulsing in nanolasers based on asymmetrically coupled cavities and study theoretically its implementation in a photonic-crystal based system. Short pulses with duration as short as 35ps with multi-GHz repetition rates are found, as well as a region giving rise to a chaotic dynamics. We also predict a parameter region where the self-pulsing bifurcation can lead to ultra-fast excitable dynamics in such a nanolaser.

Pulse train control in an excitable micropillar laser with delayed optical feedback (Conference Presentation)

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.

Spiking and pulse train dynamics in a neuromimetic micropillar laser (Conference Presentation)

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.

Self-pulsing and nonlinear dynamics in micro and nanolasers

We present recent experimental and theoretical results on the nonlinear dynamics of semiconductor micro and nanolasers. Self-pulsing dynamics is encountered both in a compact and monolithic microlaser with intracavity integrated saturable absorber and in photonic crystal nanolasers. We propose a scheme for achieving self-pulsing in nanolasers based on asymmetrically coupled cavities and study theoretically its implementation in a photonic-crystal based system. On the other hand, short pulses with duration as short as 35 ps with multi-GHz repetition rates are found. Short pulses are experimentally evidenced in a micropillar laser with saturable absorber together with excitable dynamics. We evidence the passage between gain-switching and excitability and show optical response with a refractory period less than 250 ps.