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 show that a monolithic and compact vertical cavity laser with intracavity saturable absorber can emit short excitable pulses. These calibrated optical pulses can be excited as a response to an input perturbation whose amplitude is above a certain threshold. Subnanosecond excitable response is promising for applications to novel all-optical devices for information processing or logical gates.

We report on a new type of optical nonlinearity in a polariton p-i-n microcavity. Abrupt switching between the strong and weak coupling regime is induced by controlling the electric field within the cavity. As a consequence bistable cycles are observed for low optical powers (2-3 orders of magnitude less than for Kerr induced bistability). Signatures of switching fronts propagating through the whole 300 x 300 µm 2 mesa surface are evidenced.PACS numbers: 71.36.+c, 42.65.Pc, 73.50.Pz, 78.55.Cr After its first observation in a Fabry Perot cavity containing Na vapor [1], optical bistability has been widely explored in solid state systems for its possible application in all optical circuits and optical computing [2]. A common approach is the use of a microcavity in which the resonance frequency depends on the stored optical energy: optical χ (3) nonlinearities, of electronic or thermal origin, have been used to obtain bistability in 1-dimensional [3,4] and 2 dimensional [5,6] photonic devices, with switching incident powers around 1 kW/cm 2 . When part of a spatially extended bistable system is switched from one stable state to the other, a front is formed between spatial regions in different states. If this front is locked, spatial solitons can be observed [7,8], otherwise the front propagates along the surface until the whole sample has switched state [9]. Recently optical bistability of microcavity polaritons has been theoretically proposed to generate propagation of switching fronts which can be used for all optical computation [10]. Polaritons are mixed exciton-photon quasiparticles resulting from the strong coupling regime of excitons with a resonant cavity mode [11]. Polaritonpolariton scattering gives rise to giant χ (3) -type nonlinearities [12,13] which have been recently shown to generate optical bistability [14]; indications of spatial solitons were also reported [15]. Another approach for optical bistability is to use the switch from strong to weak coupling regime due to exciton bleaching at high pumping power [16,17]. This method has been theoretically proposed in 1996 [18], and some experimental indication has been reported in 2004 [19]. In this work, we experimentally demonstrate low-power optical bistability based on a new non-linear mechanism. Switching between strong and weak coupling regime is induced controlling the internal electric field of a p-i-n microcavity. Well defined hysteresis cycles are observed both scanning the external bias or the optical power. * now at CNISM UDR Pavia and Dipartimento di Elettronica, Università degli studi di Pavia, via Ferrata 1, 27100 Pavia, Italy A model including the changes of optical and electronic properties between the strong and weak coupling regime is developed and gives a good overall description of the observed cycles. Finally we show that a local excitation can produce commutation of the whole mesa. The sample (see Fig. 1 a)) is described in details in ref. [20]. Grown on an n-doped GaAs substrate, an undoped GaAs cavity containing 3 In 0.05 Ga 0....