Delphine Wolfersberger

Build up mechanisms of (1+1)-dimensional photorefractive bright spatial quasi-steady-state and screening solitons

A (1+1)-dimensional model is studied numerically to evidence the build up mechanisms of photorefractive solitons, from the characteristic carrier recombination time, through the quasi-steady-state soliton, to the screening soliton. Three different build up regimes are evidenced and their domain of existence are computed. The transient quasi-steady-state soliton is shown to be characterized by two constants: its normalized width and its normalized build up time response multiplied by its peak intensity over dark irradiance. This latter assertion allows us to predict the photorefractive soliton response time for various optical powers. It is thus compared to existing experimental results.

All-optical interconnects using Airy beams.

We analyze numerically optical waveguide structures in photorefractive media induced by one or two incoherent counter-propagating (CP) Airy beams. Under nonlinear focusing conditions, we show that for a single Airy beam or for two CP beams with various input positions, multiple waveguiding structures can be photo-induced in the medium. Optical Gaussian beams can therefore be guided with a deflecting trajectory and/or even split into several output beams. These results enable new configurations for all-optical interconnections.

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.

Experimental study of the self-focusing process temporal behavior in photorefractive Bi12TiO20

A systematic experimental study of the photorefractive self-focusing process in Bi12TiO20 is conducted and its results are successfully compared to previous and new theoretical work.

The r33 electro-optic coefficient of Er:LiNbO3

By exploiting a Mach–Zehnder interferometer, the r33 electro-optic coefficient of erbium-bulk-doped lithium niobate crystals grown by the Czochralski technique was measured depending on the erbium content. The r33 coefficient decreases with the erbium concentration. Such a trend has been connected with both the reduction of the lattice parameter, measured by high resolution x-ray diffraction, and the increase of lattice defects.

Coherent collisions of infrared self-trapped beams in photorefractive InP:Fe

In this paper, we experimentally demonstrate collisions between two copropagating parallel coherent beams inside the photorefractive semiconductor iron doped indium phosphide (InP:Fe) at λ=1064 nm.

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.

Spatiotemporal dynamics of counterpropagating Airy beams.

We analyse theoretically the spatiotemporal dynamics of two incoherent counterpropagating Airy beams interacting in a photorefractive crystal under focusing conditions. For a large enough nonlinearity strength the interaction between the two Airy beams leads to light-induced waveguiding. The stability of the waveguide is determined by the crystal length, the nonlinearity strength and the beam’s intensities and is improved when comparing to the situation using Gaussian beams. We further identify the threshold above which the waveguide is no longer static but evolves dynamically either time-periodically or even chaotically. Above the stability threshold, each Airy-soliton moves erratically between privileged output positions that correspond to the spatial positions of the lobes of the counterpropagating Airy beam. These results suggest new ways of creating dynamically varying waveguides, optical logic gates and chaos-based computing.

Bifurcation to chaotic low-frequency fluctuations in a laser diode with phase-conjugate feedback

We unveil theoretically the bifurcations to chaotic low-frequency fluctuations (LFF) in a laser diode with phase-conjugate feedback (PCF). LFF occur from a chaotic itinerancy among destabilized limit-cycle attractors that correspond to the external-cavity modes (ECMs) of the PCF laser system and with a directional motion toward a self-pulsating dynamics of increasing frequency and larger output power. When increasing the feedback strength, the frequency of the fast-pulsing dynamics changes about a multiple of the external-cavity frequency, which is a unique feature of LFF in a laser diode with PCF.

Super-harmonic self-pulsations from a time-delayed phase-conjugate optical system

We provide experimental evidence of super-harmonic self-pulsation in a laser diode with a phase-conjugate optical feedback (PCF), i.e., time-periodic nearly sinusoidal oscillating output power at a frequency being multiple of the external-cavity frequency that corresponds to the long-standing predictions of so-called “external-cavity mode” [G. P. Agrawal and J. T. Klaus, Opt. Lett. 16, 1325–1327 (1991)]. High-harmonic self-pulsations have been so far limited to configurations with long time-delay, hence to relatively small frequencies (<1–2 GHz). By contrast, the reported self-pulsating solutions from PCF are stable in a larger range of feedback strength and with higher-order harmonic number when decreasing the external-cavity time-delay.