Photorefractive Spatial Solitons

Abstract

We present an overview of the experimental and theoretical understanding of spatial solitons in photorefractive materials. There are three generic types at present: quasi-steady-state, screening and photovoltaic solitons. The quasi-steady-state solitons (predicted and discovered first) exist during the slow screening process of an externally applied field in bright and dark realizations and in one and two transverse dimensions.(1,2) The screening solitons were predicted and recently observed(3-7) in a photorefractive material (SBN) with an externally applied field which is nonuniformly screened at steady-state. The photovoltaic solitons were predicted and observed(8,9) in photorefractive materials with a strong photovoltaic current (e.g. LiNbO3) and use the refractive index perturbation associated with the photovoltaic field to guide and confine the planar soliton. By and large, none of these solitons have properties similar to those of conventional Kerr solitons. Perhaps the most important distinctions between Photorefractive and Kerr solitons is the existence of photorefractive solitons at microwatts and lower power levels and in two transverse dimensions. Photorefractive solitons also induce waveguides that can guide other beams. When a guided beam is at a non-photosensitive wavelength it be much more intense than the soliton that induced the waveguide. Thus, a 1-microwatt soliton can guide a 1-watt beam.(10) All these unique features suggest the practicality of using photorefractive solitons for beam steering, optical wiring, interconnects, and other nonlinear optical devices.