We analyze the nonlinear propagation of a one dimensional Airy beam inside a photorefractive medium. Under nonlinear focusing conditions, the Airy beam splits into a weak accelerating structure and a soliton-like beam called ”off-shooting soliton”. Experimental measurements and numerical results related to the soliton-like structure are compared to conventional gaussian solitons and find good agreement in terms of profile, width and amplitude. We demonstrate that its profile is also preserved through propagation over long distances. Finally we identify the different parameters for generating the ideal Airy beam off-shooting soliton i.e. the one closest to the conventional theoretical soliton.
We study numerically and experimentally the transition from convective to absolute dynamical instabilities in an optical system composed of a bulk photorefractive crystal subjected to a single optical feedback. We demonstrate that the convective regime is directly related to the bistability area in which the homogeneous steady state coexists with a Turing pattern solution. Outside this domain, the system exhibits either a homogeneous steady state or an absolute dynamical regime. Moreover, an external background illumination applied onto the nonlinear medium is used as an external parameter for controlling the size of the bistability area. We question the role of this parameter and show how the background illumination makes the bistability area even larger.
We analyze numerically and experimentally the pattern formation process in an optical system composed of a bulk photorefractive crystal subjected to a single optical feedback. In this configuration, the system admits an homogeneous solution for low coupling strength. Increasing the coupling strength leads to a sub-critical bifurcation which leads to a pattern state. Such a bifurcation gives access to a well-defined hysteresis. In this paper we demonstrate that the size of the bistable area can be adjusted by different system parameters such as the intensity of the input beam, the power of an external background illumination and more interestingly by the feedback mirror tilt angle.
In this paper, we deal with optical Airy beams propagating in a nonlinear photorefractive crystal. We first study the dynamics of one Airy beam and show that it evolves in two stages: when we apply a focusing nonlinearity on the crystal, the output beam first turns into an off-shooting soliton. Then we observe a relaxation-type dynamics towards a focused redistributed solution where an Airy-like profile and the previous off-shooting soliton are superimposed. In a second step we add a second Airy beam counterpropagating in the nonlinear crystal. We show that the interactions induced by counter-propagating Airy beams allow for achieving complex waveguiding structures that would otherwise require the counter-propagating interactions of more than two Gaussian beams. Finally we present that the stationary waveguide structures shown previously can be switched to spatiotemporally varying structures by tuning the photorefractive nonlinearity of the system. The system dynamically evolves from a steady-state regime to time-dependent stable and turbulent states where the off-shooting solitons begin to move first periodically then erratically around specific Airy-induced output positions. These localized spatiotemporal dynamics are induced by the peculiar energy distribution of the counterpropagating Airy beams.
We analyze pattern formation in an optical system composed of a bulk photorefractive crystal subjected to a single
optical feedback. Far above the modulational instability threshold, in a highly nonlinear regime we report on a turbulent
spatio-temporal dynamics that leads to rare and intense localized optical peaks. We demonstrate that the statistics and
features of those peaks correspond to two dimensional rogue events. These optical rogue waves arise erratically in space
and time and live for a typical time of the same order of the response time of the photorefractive material.
We demonstrate theoretically and experimentally that modulation instability leading to optical pattern formation
can arise by using non conventional 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 non linearly on both the vortex topological charge
and the intensity of the input beam.
An experimental analysis of the dynamics of optical patterns emerging from a photorefractive two-wave mixing
geometry is investigated. The dynamics appears in the system, when a tilted single feedback mirror gives rise to an
advection-like effect. Depending on the nonlocal coupling (introduced by the tilting angle) between the two
counterpropagating beams, the strength of the nonlocal response of the nonlinear photorefractive bulk medium and the
distance mirror-crystal, we report on: the seeding of new pattern geometry, the inversion of pattern transverse phase
velocity and the bifurcation from convective to absolute instabilities.
We present the observation of the manipulation of modulational instability in a nonlinear dissipative system by a
periodic photonic lattice. We use a setup based on a photorefractive BaTiO<sub>3</sub> crystal in a single feedback mirror
configuration leading to the formation of hexagonal patterns. Additionally, we impose an optical lattice to induce one or
two-dimensional photonic band-gap structures with variable parameters. We show that by varying the lattice periodicity,
thus adjusting the transverse spatial frequencies associated to the bandgap, we can induce patterns of particular
symmetry or suppress the modulational instability when the position of the lattice bandgap coincides with the instability