Search

Excitability, encountered in numerous fields from biology to neurosciences and optics, is a general phenomenon characterized by an all-or-none response of a system to an external perturbation. When subject to delayed feedback, excitable systems can sustain multistable pulsing regimes, which are either regular or irregular time sequences of pulses reappearing every delay time. Here, we investigate an excitable microlaser subject to delayed optical feedback and study the emergence of complex pulsing dynamics, including periodic, quasiperiodic and irregular pulsing regimes. This work is motivated by experimental observations showing these different types of pulsing dynamics. A suitable mathematical model, written as a system of delay differential equations, is investigated through an in-depth bifurcation analysis. We demonstrate that resonance tongues play a key role in the emergence of complex dynamics, including non-equidistant periodic pulsing solutions and chaotic pulsing. The structure of resonance tongues is shown to depend very sensitively on the pump parameter. Successive saddle transitions of bounding saddle-node bifurcations constitute a merging process that results in unexpectedly large locking regions, which subsequently disconnect from the relevant torus bifurcation curve; the existence of such unconnected regions of periodic pulsing is in excellent agreement with experimental observations. As we show, the transition to unconnected resonance regions is due to a general mechanism: the interaction of resonance tongues locally at an extremum of the rotation number on a torus bifurcation curve. We present and illustrate the two generic cases of disconnecting and of disappearing resonance tongues. Moreover, we show how a maximum and a minimum of the rotation number appears naturally when two torus bifurcation curves undergo a saddle transition (where they connect differently)., 11 figures

Vibrational resonance amplifies a weak low-frequency signal by use of an additional non-resonant high-frequency modulation. The realization of weak signal enhancement in integrated nonlinear optical nanocavities is of great interest for nanophotonic applications where optical signals may be of low power. Here, we report experimental observation of vibrational resonance in a thermo-optically bistable photonic crystal optomechanical resonator with an amplification up to +16 dB. The characterization of the bistability can interestingly be done using a mechanical resonance of the membrane, which is submitted to a strong thermo-elastic coupling with the cavity., 10 pages, 5 figures

Chaos and synchronization are important and ubiquitous phenomena in nature. Chaos synchronization spontaneously emerges in the collective dynamics of coupled nonlinear oscillators; however, its control remains a challenge at the nanoscale. Here, we present an experimental and theoretical investigation of synchronization on the route to chaos and in the chaotic regime in mechanically coupled electro-optomechanical nanocavities. In this system an integrated electroactuation enables one to drive the mechanical normal modes in the nonlinear regime while the mechanical displacement is transferred to an optical probe which provides a direct readout access to both their amplitude and phase responses. Using a single low-frequency modulation of the force applied to each normal mode, we induce a chaotic dynamics in the coupled nanoresonators. By applying a simultaneous force modulation on each of the normal modes, we generate chaos at two distinct carrier frequencies referred to as bichromatic chaos. The mode amplitudes are synchronized all the way on the route to chaos as well as in the chaotic regime. Meanwhile, their phases experience complex dynamics with imperfect synchronization in the chaotic regime. These results set the ground for applications of mechanical nanoresonators in areas such as metrology, multispectral chaotic encryption, and analog computing.

Coupled nano-opto-electromechanical systems (NOEMS) are ideal platform to test physical concepts applied to mechanics. Large amount of various photonic structures able to couple to external fields were used to exhibit coherent perfect absorption (CPA) [1] – [3] .

Excitable systems with delayed feedback are important in areas from biology to neuroscience and optics. They sustain multistable pulsing regimes with different number of equidistant pulses in the feedback loop. Experimentally and theoretically, we report on the pulse-timing symmetry breaking of these regimes in an optical system. A bifurcation analysis unveils that this originates in a resonance phenomenon and that symmetry-broken states are stable in large regions of the parameter space. These results have impact in photonics for e.g. optical computing and versatile sources of optical pulses., 5 pages, 4 figures

International audience; Spiking micro-lasers are interesting neuromorphic building blocks to realize all-optical spiking neural networks. Optical spike-based computing offers speed and parallelism of optical technologies combined with a sparse way of representing information in spikes, thus with a potential for efficient brain-inspired computing. This article reviews some of the latest advances in this field using single and coupled semiconductor excitable micro-lasers.

International audience; Nonlinear pulse propagation is a major feature in continuously extended excitable systems. The persistence of this phenomenon in coupled excitable systems is expected. Here, we investigate theoretically the propagation of nonlinear pulses in a 1D array of evanescently coupled excitable semiconductor lasers. We show that the propagation of pulses is characterized by a hopping dynamics. The average pulse speed and bifurcation diagram are characterized as a function of the coupling strength between the lasers. Several instabilities are analyzed such as the onset and disappearance of pulse propagation, and a spontaneous breaking of the translation symmetry. The pulse propagation modes evidenced are specific to the discrete nature of the 1D array of excitable lasers. Linear oscillators coupled with springs to nearest neighbors exhibit wave propagation. This phenomenon is persistent when considering the continuous limit, i.e. when considering an elastic rope. In this limit, the wave dispersion relation is linear, unlike the discrete case of coupled systems where it is nonlinear. Here we study the propagation of localized nonlinear wave pulses in coupled excitable systems. Excitable oscillators play a fundamental role in understanding the activity of neurons, cardiac tissue, and oscillatory chemical reactions. Based on a model of a 1D array of excitable semiconductor lasers, we show that pulse propagation is characterized by a hopping dynamics and that it displays a rich variety of bifurcations. Counter-intuitively, we observe that pulses do not persist in the continuous limit.

Micropillar lasers with integrated saturable absorber (LSA) have been demonstrated to show important neuromimetic properties such as ultrafast excitable behavior, temporal summation, relative & absolute refractory periods and spike latency. In this work we study a LSA with self delayed connection which can show regenerative spiking. Such delayed self connections called as autpases are found in living nervous systems in regions essential for memory. The characteristic response of a single LSA is a 200 ps wide pulse emitted in response to an optical perturbation above the excitable threshold. In the presence of an external feedback, a single above threshold perturbation will trigger a train of pulses. Additional perturbations are capable of retiming an existing pulse train and adding or removing a pulse train, thus enabling all optical control of spikes. If the system is perturbed under correct conditions several times during the external cavity roundtrip time τ, we can create several coexisting pulse trains in the cavity which are essentially the input perturbation repeating with the time period τ. This can be seen as an optical buffer for spikes. However, in the long term these seemingly independent pulses interact and converge towards a stable solution. This final stable solution is based on the input sequence, thus this long term behavior can be seem as an associative memory. Numerical simulations of the Yamada model with delayed feedback and noise are presented and found to be in good agreement with the experimental observations. All the observed dynamics of spike interaction and convergence can be explained solely based with the internal dynamics of carriers.

As sources of short, high-amplitude light pulses, self-pulsing lasers are central to many applications, including telecommunications and neuromorphic photonic computing. We consider an excitable semiconductor micropillar laser subject to delayed optical feedback. The microlaser alone displays an all-or-none response to external perturbations. In the presence of feedback, a first excitable pulse can regenerate itself after a delay time, thus resulting in a train of pulses with repetition rate close to the delay time. Several pulse trains can be triggered and sustained simultaneously. Although they can seem independent on the timescale of the experiment, recent work showed that all pulsing patterns correspond to very long transient towards one of the stable periodic solutions of the system. Only stable solutions corresponding to equidistant light pulses in the feedback cavity were observed. We demonstrate experimentally and numerically that stable periodic solutions corresponding to non-equidistant pulses can also exist and be stable. A bifurcation analysis of a suitable mathematical model unveils the conditions on the timescales of the gain and absorption variables for such solutions to exist. We show that the long-term timing between non-equidistant pulses is fixed by the system parameters and does not depend on the initial timing between the pulse trains. Moreover, the bifurcation analysis demonstrates that, for a given number of coexisting pulses in the feedback cavity, only one configuration is stable, corresponding either to equidistant pulses or non-equidistant pulses with a fixed interpulse timing. The latter originates from a period doubling bifurcation and can also be viewed as a symmetry breaking phenomenon of the time-shift symmetry sustained by the system. Our results provide a better understanding of pulsing dynamics in an excitable laser with delayed feedback. Because the only ingredients here are excitability and feedback, we believe our results may be of interest beyond the scope of laser dynamics.

In this work, we study the nonlinear dynamics of two elastically coupled micro-membranes. These MHz-resonators are capacitively driven by a pair of integrated interdigitated electrodes. Each membrane is suspended over a 350 nm air gap constituting a Fabry-Perot cavity used to optomechanically read-out its displacement with a 633 nm laser. The linear regime analysis of the system reveals a strong constitutive difference of the resonators natural frequencies as well as a weak coupling regime. The system is strongly driven to reach a nonlinear regime that is described with a two coupled Duffing resonators model. We report the emergence of classical chaos when the resonant driving force is modulated with a low frequency (kHz) pump. The experimental bifurcation diagrams corresponding to the change of low frequency pump and amplitude of this modulation are numerically reproduced. We discuss the dissipative aspect of the problem that plays a crucial role in the pump frequency range allowing the chaotic regimes to be reached. This system constitutes an interesting base for the fundamental investigation of the collective dynamics of an array of nonlinear resonators. Additionally, our bifurcation diagrams exhibits several brutal dynamical changes often referred as “extreme events”. We consider using these highly sensitive points in the parameters space as working points for chaos based sensing applications.

In ordinary consciousness, noise is associated with the term “hindrance”; it is considered as a nuisance that can lead to communication or signal transmission failure or prevent the detection of a weak signal to be measured. However, under certain conditions the impact of noise can be counter-intuitively a resource. In nonlinear systems, noise can induce novel regimes leading to the formation of synchronized structures, coherence between the output and the input of resonators or even to the amplification of weak signals. In other words, noise can play a constructive role, with potential benefits for signal processing or measurement for instance. Single or coupled Nano-Opto-ElectroMechanical resonators whose design is based on suspended photonic crystal membrane could be used as a toy-system to pursue two main goals: stochastic amplification and chaos. As such noise-aided processes might have a strong impact in noise-assisted applications including signal processing or sensing.

International audience; We review experimental and theoretical results on the computing properties of single spiking micropillar lasers and present numerical studies of propagation and computing in chains of evanescently coupled micropillar lasers. Single mi-cropillar lasers are shown to behave as ultrafast optical neurons with sub-nanosecond spike times. They also possess absolute and relative refractory times, spike latency and show temporal summation. With delayed optical feedback, they emulate an autapse. These basic neural properties can be used for simple photonic computing. We show by numerical simulations of a chain of coupled spiking micropillar lasers that basic logical operations can be implemented in photonic circuits, as well as temporal pattern recognition based on the collision properties of pulses in this chain.

An excitable semiconductor micropillar laser with delayed optical feedback is able to regenerate pulses by the excitable response of the laser. It has been shown that almost any pulse sequence can, in principle, be excited and regenerated by this system over short periods of time. We show experimentally and numerically that this is not true anymore in the long term: rather, the system settles down to a stable periodic orbit with equalized timing between pulses. Several such attracting periodic regimes with different numbers of equalized pulse timing may coexist and we study how they can be accessed with single external optical pulses of sufficient strength that need to be timed appropriately. Since the observed timing equalization and switching characteristics are generated by excitability in combination with delayed feedback, our results will be of relevance beyond the particular case of photonics, especially in neuroscience., 5 pages, 4 figures, 41 references

The lateral wet oxidation of thin layers of Al-rich semiconductors is of prime importance for the fabrication of electrically injected vertical-cavity lasers, and in many areas of nanophotonics. The authors introduce a reaction-diffusion model of oxidation-front propagation based on the chemical oxidation processes, one that includes the effects of anisotropies and applies to any (possibly nonconvex) initial geometry. Numerical simulations show excellent agreement with experiment. This method is general and opens the way to the fine control of wet-oxidation fronts, which has numerous practical applications in terms of device creation.

We report on a mode locked semiconductor laser for high-power pulse generation in the 810-nm waveband. This is based on a novel GaAsP/GaInP single quantum-well structure, with Aluminum-free active region. Average output powers higher than 40 mW are reported in narrow ridge two-section devices. A 1.65-mm-long laser with 70 μm saturable absorber yields a stable mode locked regime at a 23-GHz repetition rate as evidenced by a record low RF linewidth of 75 kHz over a wide range of gain currents. Other laser dynamics are also reported at lower frequencies.

We report experimental and theoretical results on the pulse train dynamics in an excitable semiconductor microcavity laser with an integrated saturable absorber and delayed optical feedback. We show how short optical control pulses can trigger, erase, or retime regenerative pulse trains in the external cavity. Both repulsive and attractive interactions between pulses are observed, and are explained in terms of the internal dynamics of the carriers. A bifurcation analysis of a model consisting of a system of nonlinear delay differential equations shows that arbitrary sequences of coexisting pulse trains are very long transients towards weakly stable periodic solutions with equidistant pulses in the external cavity.

Excitable lasers with saturable absorbers are currently investigated as potential candidates for low level spike processing tasks in integrated optical platforms. Following a small perturbation of a stable equilibrium, a single and intense laser pulse can be generated before returning to rest. Motivated by recent experiments [Selmi, Phys. Rev. E 94, 042219 (2016)10.1103/PhysRevE.94.042219], we consider the rate equations for a laser containing a saturable absorber (LSA) and analyze the effects of different initial perturbations. With its three steady states and following Hodgkin classification, the LSA is a Type I excitable system. By contrast to perturbations on the intensity leading to the same intensity pulse, perturbations on the gain generate pulses of different amplitudes. We explain these distinct behaviors by analyzing the slow-fast dynamics of the laser in each case. We first consider a two-variable LSA model for which the conditions of excitability can be explored in the phase plane in a transparent manner. We then concentrate on the full three variable LSA equations and analyze its solutions near a degenerate steady bifurcation point. This analysis generalizes previous results [Dubbeldam, Phys. Rev. E 60, 6580 (1999)1063-651X10.1103/PhysRevE.60.6580] for unequal carrier density rates. Last, we discuss a fundamental difference between neuron and laser models., SCOPUS: ar.j, info:eu-repo/semantics/published

As sources of short, high-amplitude light pulses, self-pulsing lasers are key elements in many applications, including telecommunications and optical processing of information. We consider here a semiconductor micropillar laser subject to delayed optical feedback. Without feedback, the laser is excitable, and, as such, displays an all-or-none response to external perturbations. Recent experiments demonstrated that, in the presence of feedback, a single external optical perturbation can trigger a train of optical pulses, whose repetition rate is determined by the delay time. These pulse trains can be controlled reliably through external optical perturbations. In particular, several pulse trains can be switched on and sustained simultaneously in the external cavity with different interpulse timing; moreover, they can be switched off or retimed, depending on the timing of the external perturbation. Such pulse trains are also referred to as localised structures or temporal dissipative solitons in the literature. We focus on the theoretical investigation of such pulsing dynamics. It has been verified experimentally and theoretically that, as long as the pulses are short compared to the delay time, the phase of the electric field is not relevant. Therefore, the Yamada model with feedback - a system of three delay differential equations for the gain G, absorption Q and intensity I - is a suitable mathematical model. We show that its temporal integration produces a wealth of pulsing dynamics in very good agreement with the experiment. The model allows us to explain the control and interaction of pulses by the interplay of the dynamics of the gain G and that of the net gain G-Q-1. We perform a bifurcation analysis of the Yamada model to unveil its complex dynamics. In particular, we show that several periodic solutions coexist and are stable. Each stable periodic solution corresponds to a pulsing regime with a given repetition rate, close to a submultiple of the delay time. These correspond to equidistant pulses in the external cavity. Importantly, no stable periodic solution with non-equidistant pulses are found. Although coexisting pulse trains may seem independent from each other on the timescale of the experiment, we demonstrate that they rather correspond to extremely long transients toward one of the available stable periodic solutions. Hence, the different pulses in the external cavity become equidistant in the long term. The rate of convergence toward the stable regime depends on the number of pulses in the external cavity, and can be determined theoretically. The maximum number of pulse trains that can be sustained simultaneously corresponds to the number of coexisting stable pulsing periodic solutions, and it strongly depends on the delay time and strength of the feedback. By providing a better understanding of pulsing dynamics in excitable lasers with feedback, these results constitute a step toward an all-optical control of pulse train duration, which may have applications in photonics. Because the mechanism for self-pulsations described here is typical and relies only on excitability and delayed feedback, our results might be of interest beyond the specific device considered here, for example for cell dynamics.

We report the formation of hybrid states of self-assembled PTCDI-C7 organic molecule excitons and surface plasmon polaritons (SPP). Ten self-assembled monolayers with no host matrix are directly evaporated onto a gold thin film forming a ultra-dense and organized, 30nm thick layer. The π- π stacking among molecules leads to the formation of H-aggregates with alignment of molecular dipole moments along the local electric field vector. This collective excitations are known to give rise to a sharp excitonic peak in absorption with large oscillator strength, which are favorable properties for the observation of strong coupling. Experimental wavevector-resolved reflectance spectra display an anticrossing, attesting the strong coupling regime with a Rabi splitting energy ΩR=102 meV at room temperature. By contrast, no anticrossing has been observed for PTCDI-C7 molecules evaporated in a different experimental condition and with a reduced local order. We interpret the observed strong coupling regime as resulting from the high degree of organization and the controlled molecular dipole orientation. Under optical pumping, we observe an enhancement of the coupling efficiency between the molecular emission and the SPP mode. This observation is consistent with the small oscillator strength of the lowest Frenkel state of exciton and to the large Stokes shift of PTCDI-C7 molecules induced by H-aggregate stacking. The use of ultra-dense layers of self-assembled molecules opens interesting perspectives for the control of the molecular dipole orientation at the nanoscale to maximize interaction with the SPP field and therefore the strong coupling strength.

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.

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.

We consider a VCSEL micropillar laser with an internal absorber section, which has been shown to show excitable behaviour before its threshold. The addition of optical feedback offers the possibility to generate a pulse train of low jitter with a repetition time that is controlled by the length of the feedback loop. We perform a bifurcation analysis of the governing Yamada equations for the intensity, gain and absorption and with delayed feedback. This reveals an increasing variety of new dynamics and a considerable degree of multistability when the delay time is increased. More concretely, we present a bifurcation/stability diagram in the plane of feedback delay and feedback strength --- the two parameters of the external feedback loop. The organising feature is a winding curve of Hopf bifurcations, which develops an increasing amount of self-intersections as the delay of the feedback is increased. Along certain parts of the Hopf curve stable periodic solutions are created, which are physically self-pulsations with an increasing number of pulses in the external cavity. Several of these self-pulsations may coexist stably, and their basins of attractions are intermingled in a complicated way. As a result, the micropillar laser is very sensitive to small perturbations and noise while in such a multistable configuration. We also find multifrequency dynamics, where the amplitude of the self-pulsations is strongly modulated.

Stochastic resonance is a general phenomenon usually observed in one-dimensional, amplitude modulated, bistable systems. We show experimentally the emergence of phase stochastic resonance in the bidimensional response of a forced nano-electromechanical membrane by evidencing the enhancement of a weak phase modulated signal thanks to the addition of phase noise. Based on a general forced Duffing oscillator model, we demonstrate experimentally and theoretically that phase noise acts multiplicatively inducing important physical consequences. These results may open interesting prospects for phase noise metrology or coherent signal transmission applications in nanomechanical oscillators. Moreover, our approach, due to its general character, may apply to various systems.

International audience; Stochastic resonance is a general phenomenon usually observed in one-dimensional, amplitude modulated, bistable systems. We show experimentally the emergence of phase stochastic resonance in the bidimensional response of a forced nanoelectromechanical membrane by evidencing the enhancement of a weak phase modulated signal thanks to the addition of phase noise. Based on a general forced Duffing oscillator model, we demonstrate experimentally and theoretically that phase noise acts multiplicatively, inducing important physical consequences. These results may open interesting prospects for phase noise metrology or coherent signal transmission applications in nanomechanical oscillators. Moreover, our approach, due to its general character, may apply to various systems.

International audience; We experimentally demonstrate strong coupling between self-assembled PTCDI-C7 organic molecules and the electromagnetic mode generated by surface plasmon polaritons (SPPs). The system consists of a dense self-assembly of ordered molecules evaporated directly on a thin gold film, which stack perpendicularly to the metal surface to form H-aggregates, without a host matrix. Experimental wavevector-resolved reflectance spectra show the formation of hybrid states that display a clear anticrossing, attesting the strong coupling regime with a Rabi splitting energy of ΩR ≃ 102 meV at room temperature. We demonstrate that the strength of the observed strong coupling regime derives from the high degree of organization of the dense layers of self-assembled molecules at the nanoscale that results in the concentration of the oscillator strength in a charge-transfer Frenkel exciton, with a dipole moment parallel to the direction of the maximum electric field. We compare our results to numerical simulations of a transfer matrix model and reach good qualitative agreement with the experimental findings. In our nanophotonic system, the use of self-assembled molecules opens interesting prospects in the context of strong coupling regimes with molecular systems.

In a large number of experiments or devices, noise is usually viewed as an undesirable disturbance, hindering the measurement sensitivity or device performances. In some circumstances however, noise-induced phenomena can help, as in the case of stochastic resonance whereby a small coherent signal gets amplified resonantly by application of external noise. Stochastic resonance occurs in a wide class of nonlinear systems, in neurobiology [1], mesoscopic physics [2], photonics [3], atomic physics [4], mechanics [5, 6]… Stochastic resonance is a kind of synchronization of the switching events. If a weak periodic forcing is applied to the oscillator, the initially symmetrical double-well potential gets tilted asymmetrically up and down, periodically raising and lowering the potential barrier. Although the periodic forcing is too weak to let the membrane switch periodically from one potential well into the other one, noise-induced hopping between the potential wells can become synchronized with the weak period forcing. This time coincidence takes place when the average waiting time between noise-induced interwell transitions is comparable with half the period of the periodic forcing. Thus stochastic resonance corresponds to the noise-assisted amplification of a weak coherent input that is too feeble to induce hopping between the two stable states.

We report the formation of hybrid states of H-aggregates of organic self-assembled aromatic polycyclic molecules (PTCDI-C7) and surface plasmons polaritons (SPP). Strong coupling has already been reported in molecular systems in a number of studies [1], for the most part in J-aggregates [2]. In our system, we consider an ultra-dense layer of self organised PTCDI-C7 molecules forming H-aggregates with no host matrix.

The occurrence of extreme events in a spatially extended microcavity laser has been recently reported [Selmi et al., Phys. Rev. Lett. 116, 013901 (2016)] to be correlated to emergence of spatiotemporal chaos. In this dissipative system, the role of spatial coupling through diffraction is essential to observe the onset of spatiotemporal complexity. We investigate further the formation mechanism of extreme events by comparing the statistical and dynamical analyses. Experimental measurements together with numerical simulations allow us to assign the quasiperiodicity mechanism as the route to spatiotemporal chaos in this system. 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 quasiperiodic extended spatiotemporal intermittency.

We present experimental measurements concerning the response of an excitable micropillar laser with saturable absorber to incoherent as well as coherent perturbations. The excitable response is similar to the behavior of spiking neurons but with much faster time scales. It is accompanied by a subnanosecond nonlinear delay that is measured for different bias pump values. This mechanism provides a natural scheme for encoding the strength of an ultrafast stimulus in the response delay of excitable spikes (temporal coding). Moreover, we demonstrate coherent and incoherent perturbations techniques applied to the micropillar with perturbation thresholds in the range of a few femtojoules. Responses to coherent perturbations assess the cascadability of the system. We discuss the physical origin of the responses to single and double perturbations with the help of numerical simulations of the Yamada model and, in particular, unveil possibilities to control the relative refractory period that we recently evidenced in this system. Experimental measurements are compared to both numerical simulations of the Yamada model and analytic expressions obtained in the framework of singular perturbation techniques. This system is thus a good candidate to perform photonic spike processing tasks in the framework of novel neuroinspired computing systems., SCOPUS: ar.j, info:eu-repo/semantics/published

Multistability between several pulsing solutions in a model of laser with saturable absorber and optical feedback is studied. High sensitivity to small perturbations is discussed and emerges as an interpretation of experimentally-observed dynamics.

We review advances on the experimental study of cavity solitons in VCSELs in the past decade. We emphasize on the design and fabrication of electrically or optically pumped broad-area VCSELs used for CSs formation and review different experimental configurations. Potential applications of CSs in the field of photonics are discussed, in particular the use of CSs for all-optical processing of information and for VCSELs characterization. Prospects on self-localization studies based on vertical cavity devices involving new physical mechanisms are also given.

The ultrafast gain and refractive index dynamics in AlInAs/AlGaAs quantum dot (QD) based semiconductor optical amplifiers is reported. Measurements in the forward bias regime indicate a complete gain recovery timescale of similar to 5 ps, while the phase dynamics occur over a much longer timescale. At increased pump powers, the impact of nonresonant carriers created by two-photon absorption is visible as an increased injection in both gain and phase dynamics. Reverse-biased measurements reveal a similar behavior to previous measurements on InAs QD devices.

We present recent experimental results on the control and dynamics of cavity solitons in a monolithic, vertical cavity surface emitting laser with saturable absorber. On one hand, the fast and independent manipulation of two laser cavity solitons is achieved and a flip-flop operation is demonstrated with a single control-beam. On the other hand, a pulsing localized structure is presented and we demonstrate the control of a pulsing multispot structure that we can switch-on and off. These results are promising in view of the obtainment of a pulsed and monolithic cavity soliton laser.

The ultrafast optical switching capabilities of an InP-based photonic crystal cavity with quantum dots (QDs) are studied. The signal is evanescently coupled into the cavity at 1.5 μm through a tapered fiber. Both surface and fiber-coupled pumping schemes are investigated and compared. It is shown that the carrier-induced nonlinear response allows the signal to be switched within time windows ranging from a few picoseconds to 20 ps for the switch ON process and from 30 to 170 ps for the switch OFF process depending on the pumping configuration and power level. The carrier-induced nonlinear effects in the bulk, the wetting layer, and the QDs are discussed and compared. From a fit of the switching dynamics to the solutions of a rate equation for carrier relaxation, we show that the main contribution to carrier dynamics governing the switching processes comes from both nonradiative and radiative carrier recombination within the InAsP wetting layer.

We show the spontaneous and controlled formation of bistable and localized laser spots in the transverse section of a monolithic vertical cavity laser with a saturable absorber. Successive incoherent writing and erasure is obtained up to 80 MHz repetition rate with a 60 ps localized excitation. We also show the formation of clusters of laser localized states. All these observations are in good qualitative agreement with existing models.

International audience; 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.

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.

International audience; Voltage bistability is demonstrated at low temperature in a biased unipolar GaAs/AlGaAs superlattice, using a design based on tunneling from a charge reservoir into a Wannier-Stark ladder and competition between nearest and next-nearest neighbor coherent injection channels. The static conduction characteristics are accounted for by a density matrix approach of coherent injection in an inhomogeneous three-level system with resistive load. Electrostatic retroaction on the energy levels is shown to provide an adequate nonlinear feedback mechanism for bistability, as well as for other instability regimes including sustained Bloch oscillation above a retroaction threshold.

The response of a bistable vertical cavity surface emitting laser to a periodic input signal display all the hallmarks of stochastic resonance. Accurate experimental measurements show the occurrence of noise-induced frequency and effective phase locking characterized by a plateau of the mean output switching rate and a minimum of the relative–phase diffusion constant, respectively.

The beneficial role fluctuations can play in the process of phase synchronization is analyzed in terms of a model with binary input and output signals. Special attention is paid to the relation between noise-induced phase synchronization and the well-known phenomenon of stochastic resonance. Analytic predictions are compared with experimental data from a vertical cavity surface emitting laser. Various measures for aperiodic stochastic resonance, frequency entrainment and stochastic phase synchronization reveal a satisfactory agreement between theory and experiment.

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.

We report on experimental evidence of neuronlike excitable behavior in a micropillar laser with saturable absorber. We show that under a single pulsed perturbation the system exhibits subnanosecond response pulses and analyze the role of the laser bias pumping. Under a double pulsed excitation we study the absolute and relative refractory periods, similarly to what can be found in neural excitability, and interpret the results in terms of a dynamical inhibition mediated by the carrier dynamics. These measurements shed light on the analogy between optical and biological neurons and pave the way to fast spike-time coding based optical systems with a speed several orders of magnitude faster than their biological or electronic counterparts.