CROSS-MODULATION COUPLING OF INCOHERENT SOLITON MODES IN PHOTOREFRACTIVE CRYSTALS

A problem of nonlinear wave propagation through a photorefractive crys tal (PRC) with drift nonlinearity has been evaluated. A class of spati ally 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 componen ts bonded by cross-modulation coupling. Light field spatial distributi ons of the components look like zero and higher order modes of their c ommon waveguide formed in PRC due to its nonlinearity. We have shown s uch a soliton is stable on distances of several diffraction lengths an d its spatial structure is robust to collisions and appreciable (more than 10% in intensity) stochastic perturbations of the intensity distr ibutions. With taking into account saturation of PRC nonlinearity, par ameters of all the soliton components (their amplitudes and widths) ch ange quasiperiodically as the soliton propagates. The components do no t exchange energy while a small fraction of the energy is emitted on f ew diffraction lengths. We discuss also a possibility of excitation of incoherent solitonlike multielectron states in conjugated polymers, f erromagnetics, and superconductors. These states could correspond to s ome mutually incoherent and self-consistent wave packets composed of e lectronic wave functions and propagating along conjugated chains or pr ominent atomic planes.