Stability of photorefractive spatial solitons

Propagation characteristics of a focused laser beam in a strontium barium niobate photorefractive crystal under reverse external electric field

The propagation characteristics of a focused laser beam in a SBN:75 photorefractive crystal strongly depend on the signal-to-background intensity ratio (R=I_s/I_b) under reverse external electric field. In the range 20>R>0.05, the laser beam shows enhanced self-defocusing behavior with increasing external electric field, while it shows self-focusing in the range 0.03>R>0.01. Spatial solitons are observed under a suitable reverse external electric field for R=0.025. A theoretical model is proposed to explain the experimental observations, which suggest a new type of soliton formation due to "enhancement" not "screening" of the external electrical field.

Forward four-wave mixing with defocusing nonlinearity

We experimentally demonstrate degenerate, forward four-wave mixing effects in a self-defocusing photorefractive medium, in both one and two transverse dimensions. We observe the nonlinear evolution of new modes as a function of propagation distance, in both the near-field and far-field (Fourier space) regions.

Two-dimensional cnoidal waves in Kerr-type saturable nonlinear media

We report theoretically the existence, classification, and basic properties of families of stationary two-dimensional cnoidal-type waves in bulk Kerr-type saturable nonlinear media. The families of two-dimensional cnoidal-type wave solutions are shown to exhibit richer features than their known one-dimensional counterparts. At low- and high-energy flows, the cnoidal patterns are predicted to be robust enough to be observable experimentally.

Incoherently coupled steady-state soliton pairs in biased photorefractive-photovoltaic materials

A theory on incoherently coupled soliton pairs for photorefractive screening solitons is developed that gives rise to incoherently coupled steady-state soliton pairs and multicomponent spatial solitons in biased photorefractive-photovoltaic materials, which result from both the bulk photovoltaic effect and the spatially nonuniform screening of the external bias field. When the bulk photovoltaic effect is neglectable, these soliton pairs are the previously studied soliton pairs for screening solitons, these multicomponent spatial solitons predict incoherently coupled multicomponent spatial solitons for screening solitons, and their space-charge field is the space-charge field of screening solitons. When the external field is absent, these soliton pairs and multicomponent spatial solitons predict incoherently coupled soliton pairs and multicomponent spatial solitons for photovoltaic solitons, and their space-charge field is the space-charge field of photovoltaic solitons. The stability of these soliton pairs and multicomponent spatial solitons is also discussed using the modulation instability theory.

Temporal development of photorefractive solitons up to telecommunication wavelengths in strontium-barium niobate waveguides

We experimentally investigate the temporal development of photorefractive solitons in strontium-barium niobate waveguides at visible and infrared wavelengths. The development times in the infrared are shown to be comparable with those in the visible. The results are compared with predictions of a previously published model.

All optical quasi-steady-state photorefractive spatial solitons

We have created a one- (rather than two-) dimensional quasi-steady-state photorefractive spatial soliton induced by a laser beam instead of an applied electric field. The formation of this type of spatial soliton depends on the intensity of the self-trapped beam, which is different from quasi-steady-state spatial solitons reported in the literature. The optically induced spatial soliton can be exploited in all optical switching applications.

Multicomponent photorefractive cnoidal waves: stability, localization, and soliton asymptotics

An algorithm of building up a different class of stable self-consistent multicomponent periodical solutions of the nonlinear Schrödinger equation--multicomponent cnoidal waves--has been formulated by the example of a nonlinear wave propagating through a photorefractive crystal with a drift nonlinear response. Exact analytical expressions, describing distribution of light field in the components, have been obtained for solutions, which include up to three mutually incoherent components. It has been shown that such cnoidal waves are stable and their spatial structure is robust to collisions with the same cnoidal waves and to stochastic perturbations of the components' intensity distributions in a sufficiently wide range of changing spatial period.

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.

(1+1)-Dimensional and (2+1)-dimensional waveguides induced by self-focused dark notches and crosses in LiNbO(3):Fe crystal

We demonstrate that (1+1)-dimensional and (2+1)-dimensional waveguides can be induced by self-focused dark notches and crosses and stored in LiNbO(3):Fe crystals. This is very valuable for information processing and integrated optics. The self-focused dark notches and crosses may be related to the formation of (1+1)-dimensional and (2+1)-dimensional photovoltaic dark spatial solitons in LiNbO(3):Fe crystals.

Waveguides formed by quasi-steady-state photorefractive spatial solitons

We show that a quasi-steady-state photorefractive spatial soliton forms a waveguide structure in the bulk of a photorefractive material. Although the optically induced waveguide is formed by a very low-power (microwatts) soliton beam, it can guide a powerful (watt) beam of a longer wavelength at which the medium is nonphotosensitive. Furthermore, the waveguide survives, either in the dark or when guiding the longerwavelength beam, for a long time after the soliton beam is turned off. We take advantage of the solitons' property of evolution from a relatively broad input beam into a narrow channel and show that the soliton induces a tapered waveguide (an optical funnel) that improves the coupling efficiency of light into the waveguiding structure.