Existence and property of spatial solitons in a photorefractive dissipative system

A dissipative photorefractive system is considered, which consists of a biased photorefractive crystal and a pump beam with a uniform spatial distribution. A signal beam couples coherently with the pump beam by codirectional degenerate two-beam coupling and hence obtains a gain. It is shown that the signal beam can evolve into a steady-state spatial bright (or dark) soliton that is a result of double balance, i.e., loss is balanced by gain, and diffraction is balanced by nonlinearity due to the spatially nonuniform screening of the applied field and to the process of two-beam coupling. Such solitons have fixed amplitude and width for fixed values of system parameters and hence are known as rigid screening (RS) solitons. RS solitons differ from previously observed screening solitons in their properties and physical origin and can exist whether the crystal possesses a focusing or a defocusing nonlinearity. If the pump beam is switched to a background illumination, RS-soliton solutions can reduce to screening-soliton solutions. Numerical simulations show that RS solitons are stable relative to small perturbations. (C) 2003 Optical Society of America