Propagation of optical beams and the properties of two-dimensional spatial solitons in media with a local saturable nonlinear refractive index

An investigation of the propagation of optical beams and the main properties of spatial solitons in three-dimensional media with a local saturable nonlinear refractive-index change is presented. The fundamental bright-soliton solution is calculated from a first integral that describes a two-value solution branch. Although both solution branches are stable in the framework of linear stability theory, the dynamic of beam propagation shows that slightly perturbed initial soliton beams do not evolve to a perfect solitary beam but lead to periodic oscillations of the amplitude. The dependence of the long-living oscillations and the possible azimuthal-symmetry breaking with formation of filaments on the saturation parameter gamma and the initial-beam parameters are studied in detail. The results are compared with experimental observations of two-dimensional photorefractive solitons. The interaction and the collision of two spatial solitons are investigated. Beam fusion can appear for parallel propagation as well for small collision angles and small phase differences for solitary beams of bath solution branches. Furthermore, solitary-beam dragging with initially overlapping beams of different directions is studied. (C) 1997 Optical Society of America.