Solitonlike propagation in photorefractive crystals with large optical activity and absorption

Photorefractive solitons of arbitrary and controllable linear polarization determined by the local bias field

We discuss and experimentally demonstrate a scheme to achieve photorefractive solitons of arbitrary linear polarization using the quadratic electro-optic effect and describe the observation of the self-trapping of a set of linear polarized beams in different positions of a paraelectric photorefractive crystal of potassium-lithium-tantalate-niobate (KLTN) biased by the inhomogeneous field produced by two miniaturized top electrodes. The polarization of the single solitons of the set is determined by the local electrostatic configuration and the underlying tunable anisotropy, which is detected through zero-field electro-activation.

(2+1)-dimensional soliton formation in photorefractive Bi12SiO20 crystals

(2+1)-dimensional spatial solitons in Bi12SiO20 (BSO) photorefractive crystals with large optical activity are experimentally demonstrated. The soliton formation when a Gaussian beam is injected at the input has been previously analyzed numerically and then experimentally investigated. We demonstrate analytically, numerically, and experimentally that by applying static electric biases of high values, the polarization rotation accelerates: this acceleration prevents the beam from broadening if the polarization rotation period becomes shorter than the diffraction length. Contemporary to this nonlinear optical activity, an induced birefringence affects the beam polarization state. Analysis of the polarization dynamics shows that the polarization changes nonuniformly across the beam (with a field dependent speed) until about 30-35 kV/cm; above this limit, the whole beam has just one polarization state. Representation on the Poincaré sphere of the polarization dynamics reveals the existence of a stable polarization trajectory closed around a polarization attractor that depends on the linear optical activity and on the photorefractive nonlinearity. The experimental soliton is well described by the analytical solutions already obtained [Fazio et al., Phys. Rev. E 66, 016605 (2002)].