Abstract

Spatial solitons in photorefractive (PR) materials¹ have been the object of growing interest during the last two years. Until now, three different types of PR solitons have been investigated. The first type stems from the nonlocal nature of the PR effect, as manifested in the dependence of the perturbation in the refractive index on the transverse derivatives of the light-intensity distribution.^1,2 Solitons of this type evolve when diffraction is exactly balanced by self-scattering (two-wave mixing) of the spatial (plane wave) components of the soliton beam. Observation of PR bright solitons of the first type^3,4 reveals that, unlike the Kerr-like solitons, these solitons may be trapped in two transverse dimensions⁵ (although the self-trapping effects are inherently asymmetric with respect to the two transverse dimensions) and maintain their stability.⁵ The most distinct properties of these solitons are independence of the absolute light intensity^1-3 (for intensities much larger than the dark irradiance) and (ii) the capability of trapping in two transverse dimensions^3-5 The second and the third types of PR solitons, called the screening soliton⁶ and the photovoltaic soliton,⁷ respectively, result from steady-state nonuniform screening (the former) or from photovoltaic fields (the latter). Unlike the first type of PR soliton, these two are both local effects (the index perturbation at any location is a function of the light intensity at the same location). As such, the shape and width (cross section) of these solitons are dependent on their intensity.

© 1995 Optical Society of America