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.

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.

Rare and extreme events are ubiquitous in many complex systems, from rogue waves in the ocean to financial crisis. In optics, extreme events have been identified in pulses propagating in nonlinear optical fibers and in the temporal dynamics of some semiconductor laser systems. Many questions remain unsolved concerning the minimum ingredients necessary to produce extreme events and how to control them. In this work, we study a dissipative, quasi 1D spatially extended system (a broad area line VCSEL with integrated saturable absorber of original design [1]) and show experimentally the occurrence in certain parameter regions of high amplitude and rare pulses (Fig. 1). Our system has the peculiar property of not displaying a complex dynamics (and thus extreme events) without spatial coupling. It is thus in stark contrast to existing studies in active dissipative systems where extreme events were found in the chaotic temporal dynamics of zero-dimensional systems [2]. We analyze the role of spatial coupling in the generation of extreme events. We experimentally demonstrate that the spatio-temporal dynamics has a characteristic correlation length smaller than the lasing area. Using cross-correlation measurements by recording the dynamics at two different locations simultaneously, we rule out the mechanism of collision of coherent structure as a mechanism for rogue wave formation in our system, as found e.g. in [3]. With the help of numerical simulations, we can identify several dynamical regimes giving rise to different long-tail probability density distributions. We calculate the Lyapunov spectrum of the numerically integrated dynamics and relate the presence of spatio-temporal chaos in our system to the occurrence of extreme events.

We study the neuromimetic properties of a micropillar laser with saturable absorber. The investigated properties are: excitability, refractory periods and temporal summation. 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. Temporal summation happens when two or more input perturbations below the excitable threshold and separated by a temporal delay lead to one excitable response. These properties could be found in excitable systems in general and neurons in particular and has been often studied in some optical systems. Fast excitable, neuron-like, response with a duration of 200 ps, which is 7 orders of magnitude faster than in biological neurons, is experimentally demonstrated. Relative and absolute refractory periods are evidenced in this system (respectively 200-350 ps and 200 ps). Temporal summation of two input perturbations is evidenced and a critical summation delay between input pulses of 600 ps in measured. The experimental results are well described qualitatively by a simple model of a laser with saturable absorber. Refractory periods and temporal summation proves that a micropillar laser with saturable absorber has a memory of its past history. Refractory periods are also responsible of the unidirectional propagation in neurons. These work pave the way for the realization of 2D networks of neuromimetic coupled micropillars laser with saturable absorber.

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.

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.

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.

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.

We present experimental and theoretical results on Vertical Cavity Surface Emitting Lasers (VCSELs) and microlasers with saturable absorber. Laser cavity solitons are experimentally demonstrated in a compact system, a broad-area VCSEL with intracavity saturable absorber. These states of light appear as 10 μm diameter self-localized microlasers that one can manipulate with external beams in the transverse plane of the laser. Cavity solitons (CS) can be thought of as optical bits for reconfigurable processing of information. We demonstrate incoherent manipulation of CS at a fast rate and present evidence of optical manipulation of self-pulsing states. Excitability is also demonstrated in a different parameter region. Excitability is characterized by: 1) existence of a threshold leading to an “all or nothing” type of response to an input perturbation, 2) appearance of a calibrated response above threshold. Excitable response is interesting for optical pulse reshaping and may be used to build logical gates. A chain of such coupled microlasers can also be used to demonstrate discrete nonlinear wave propagation, with application to e.g. optical delay lines or neuro-inspired processing. A novel scheme to attain self-pulsing in nanocavity lasers will also be presented, thus showing the possible scaling down of the previous system.

Microwave calcining of conventionally prepared (mixed oxides) as well as sol-gel prepared lead zirconate titanate (PZT) powders was investigated. Conventionally prepared PZT was calcined with microwave power at 720°C for 45 min, whereas conventional calcination requires 4 h at 800°C. The sol-gel PZT was calcined with microwave power at 600°C for 40 min, whereas 5 h are needed when a conventional furnace is used at the same temperature. Beside reducing the calcining temperature and time, microwave heating also leads to a more uniform particle size distribution in both cases.

There is considerable interest in the development of microwave ceramic phase shifters because of limitations of currently available ferrite and PIN diode phase shifters regarding cost and reliability and complexity. Ceramic phase shifters may provide a cost breakthrough for the phased array antenna designer while maintaining low insertion losses and low drive power and high power handling capacity. This paper describes ceramic phase shifters which utilize a ferroelectric material [(Ba-Sr)TiO3 series] for obtaining phase shifts from changes in dc biasing fields. Also, the dielectric properties are measured as a function of dc biasing fields, frequency and temperature for a few compositions of barium-strontium titanate material. For the frequency range of 400 MHz to 5 GHz, differential phase shift is obtained by a dc voltage-controlled lumped barium-strontium titanate capacitor in a coaxial line or stripline medium. For 5 to 18 GHz frequency range, a barium-strontium titanate material which partially or completely fills the rectangular waveguide is required for the construction of a ceramic phase shifter.

Sol gel processing of ceramic materials has attracted much interest in the past decade because of its inherent advantages in homogeneity of the resulting powder, fine grain size, high purity, and ability to mix disparate materials well. Sol gel processing is particularly apt to tunable electroceramics such as barium strontium titanate (BST) because of the fine grain size and purity desirable in such materials. It may be desirable to develop a semiautomatic system to produce the tunable ceramic powder, thin film and ceramic devices. Thin film tunable ceramics can be deposited on to a substrate with or without conductive traces by using a microwave plasma deposition system. In this paper, we have shown such a system incorporating microwave power for calcination, binder burn out and final sintering to a near net shape manufacturing of ceramic devices. This paper also describes the sol gel processing method for BST and compares properties of materials prepared by the sol gel method and the more conventional carbonate and oxide powder method.

It is shown that ferroelectric phase shifters for electronically steerable antenna systems can be realized by using an appropriate composition (e.g., Ba/sub 0.45/Sr/sub 0.55/TiO/sub 3/) of barium strontium titanate material in a suitable transmission line medium (waveguide, coaxial line, or microstrip line). Ferroelectric phase shifters will have several advantages over other types of phase shifters, including high power handling capacity, simple driver circuitry, low drive power, and low cost. Because of the large variation (more than 50%) of dielectric constant with DC biasing voltage, the development of low-loss tangent materials due to the addition of small quantities of Fe or Hi or Mn, and sol-gel processing of ultrapure and fine ceramic powders, (Ba-Sr)TiO/sub 3/ materials are particularly suitable for ferroelectric phase shifter applications.<>

The calcination and sintering behavior of barium strontium titanate was investigated using microwave power absorption. With microwave power, BaCO3, SrCO3 and TiO2 powders were calcined at 1100°C for 45 min, whereas conventional calcination requires typically more than 5 h at 1150°C. Pressed samples of microwave calcined Ba0.65Sr0.35TiO3 were sintered in 30 min at 1350°C using a microwave cavity. The permittivity and loss tangent of the sintered samples were also measured. It is shown that microwave calcination and sintering lead to an improvement in the dielectric properties.

Microwave power was used to burn out binder from tape-casted barium strontium titanate ceramics. Compared with conventional methods of binder burn out, microwave heating offers some distinctive advantages. The binder burn out process was completed using microwave power at lower temperature and less time. By characterizing the dielectric properties of the tapes at different stages of microwave heating, a better understanding of microwave and conventional binder burn out mechanisms is realized.

There is considerable interest in the development of microwave ceramic phase shifters because of limitations of currently available ferrite and PIN diode phase shifters regarding cost and reliability and complexity. Ceramic phase shifters may provide a cost breakthrough for the phase array antenna designer while maintaining low insertion loss and low drive power and high power handling capacity. This paper describes a ceramic phase shifter which utilizes a ferroelectric material for obtaining phase shifts from changes in dc biasing fields. Also, the dielectric properties were measured as a function of dc biasing fields, frequency, and temperature for a few compositions of barium-strontium titanate material.

The sintering behavior of coprecipitated Sb-doped SnO2 was investigated using microwave power absorption. With microwave power, samples were sintered at 1450°C for 20 min and showed a density as high as 99.9% of theoretical. However, samples fired in conventional electric furnace at the same temperature for 4 h showed only 60% of theoretical density. Microwave sintering also led to improvement in terms of uniform structure and electrical properties.