Screening-photovoltaic spatial solitons in biased photovoltaic–photorefractive crystals and their self-deflection

Abstract

Steady-state dark (or bright) spatial solitons are predicted for biased photovoltaic–photorefractive materials when the diffraction of an optical beam is exactly compensated for by nonlinear self-defocusing (or self-focusing) that is due both to the photovoltaic effect and to spatially nonuniform screening of the applied field. These solitons differ from previously observed steady-state photorefractive or photovoltaic spatial solitons in their properties and experimental condition. These biased photovoltaic solitons are known as the screening-photovoltaic solitons. If the bias field is much stronger than the photovoltaic field, then the screening-photovoltaic solitons are just like the screening solitons. If the applied field is absent, they degenerate into photovoltaic solitons in the closed-circuit condition. We investigate the self-deflection process of bright screening-photovoltaic solitons by taking diffusion effects into account. By use of perturbation techniques it is found that the center of the optical beam moves on a parabolic trajectory and, moreover, that the central spatial-frequency component shifts linearly with the propagation distance. Both the spatial deflection and the angular deviation are proportional to the sum of two dimensionless quantities that are associated with the bias field and the photovoltaic field, respectively. The drift process and the photovoltaic process play an equivalent role in the self-bending process.