Cross-modulation coupling of incoherent soliton modes in photorefractive crystals

A problem of nonlinear wave propagation through a photorefractive crystal (PRC) with drift nonlinearity has been evaluated. A class of spatially localized solitonlike solutions with finite energy has been found. Solutions of this class can be considered as multicomponent solitons, combined by two or more mutually incoherent self-consistent components bonded by cross-modulation coupling. Light field spatial distributions of the components look like zero and higher order modes of their common waveguide formed in PRC due to its nonlinearity. We have shown such a soliton is stable on distances of several diffraction lengths and its spatial structure is robust to collisions and appreciable (more than 10% in intensity) stochastic perturbations of the intensity distributions. With taking into account saturation of PRC nonlinearity, parameters of all the soliton components (their amplitudes and widths) change quasiperiodically as the soliton propagates. The components do not exchange energy while a small fraction of the energy is emitted on few diffraction lengths. We discuss also a possibility of excitation of incoherent solitonlike multielectron states in conjugated polymers, ferromagnetics, and superconductors. These states could correspond to some mutually incoherent and self-consistent wave packets composed of electronic wave functions and propagating along conjugated chains or prominent atomic planes.