Enhanced complexity of optical chaos in a laser diode with phase-conjugate feedback.

We demonstrate numerically that a semiconductor laser subjected to phase-conjugate feedback (PCF) can exhibit an enhancement in the complexity of chaos by comparison to conventional optical feedback. Using quantifiers from spectral analysis and information theory, we demonstrate that under similar parametric conditions, PCF exhibits a larger chaotic bandwidth and higher spectral flatness and statistical complexity. These properties are of utmost importance for applications in secure communications and random number generation.

Spatial rogue waves in a photorefractive pattern-forming system.

We have experimentally analyzed pattern formation in an optical system composed of a bulk photorefractive crystal subjected to a single optical feedback. In a highly nonlinear regime far above the modulational instability threshold, we are reporting on turbulent spatiotemporal dynamics that leads to rare, intense localized optical peaks. We have proven that the statistics and features of those peaks correspond to the signatures of two-dimensional spatial rogue events. These optical rogue waves occur erratically in space and time and live typically the same amount of time as the response time of the photorefractive material.

Nonlocal effect on vortex-induced pattern dynamics.

We show experimentally and theoretically that the interplay between a vortex-induced pattern rotation and an optical feedback nonlocality-induced pattern drift leads to new dynamics and geometries of optical pattern formation. First, the vortex-induced pattern rotation and the nonlocality-induced drift can annihilate each other, resulting in the formation of static zones in the near field of the otherwise drifting pattern. Second, increasing the external mirror tilt leads to new pattern solutions that are composed of wave vectors of different amplitudes and directions, resulting in a multistriped pattern geometry.

Vortex induced rotation dynamics of optical patterns.

We demonstrate that modulation instability leading to optical pattern formation can arise by using nonconventional counterpropagating beams carrying an orbital angular momentum (optical vortices). Such a vortex beam is injected into a nonlinear single feedback system. We evidence different complex patterns with peculiar phase singularities and rotating dynamics. We prove that the dynamics is induced by the vortex angular momentum and the rotation velocity depends nonlinearly on both the vortex topological charge and the intensity of the input beam.

Experimental control of pattern formation by photonic lattices.

We study the control of modulational instability and pattern formation in a nonlinear dissipative feedback system with a periodic modulation of the material refractive index. We use a one-dimensional photonic lattice in a single-mirror feedback configuration and identify three mechanisms for pattern control: bandgap suppression of instability modes, periodicity induced pattern modes, and orientational pattern control.

Self-focusing of a single laser pulse in a photorefractive medium

An original experimental and theoretical time-resolved study of a single laser pulse self-focusing in a nonlinear photorefractive medium is reported. The behavior of the self-focusing process is experimentally observed in a photorefractive Bi12TiO20 crystal during the 5 ns pulse duration of a doubled Nd:YAG (yttrium aluminum garnet) laser. A theoretical interpretation is provided, based on a simple model of photorefraction on the nanosecond time scale.

Simulation of the temporal behavior of soliton propagation in photorefractive media.

We consider the propagation of light beams in photorefractive media in the framework of a (1+1)-dimensional model. The Kukhtarev band transport model is introduced both in a time-dependent differential equation describing the evolution of the space charge field and in a nonlinear wave propagation equation. This latter is then numerically solved with a beam propagation method routine. The evolution in time and space of an initially diffracting laser beam is simulated as a function of initial profiles and waists. The beam is shown to go through a transient overfocused state prior to relaxing to a steady state soliton. Additional features such as the stability condition of the system or effects such as optical branching and soliton interactions are studied.