Optical channel waveguides formed by upconverted photobleaching of dye-doped polymer film in regime of dark spatial soliton

We demonstrate theoretically and experimentally that an initially Gaussian optical beam (633 nm wavelength) sent through a pi-step phase mask and laun ched into a thin film of polymer poly(methyl methacrylate) doped with laser dye 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)4H-pyran known as DCM evolves into a spatial structure similar to a dark spatial soliton. This takes place due to nonlinear mechanism of upconverted photobleaching o f the dye-doped polymer. The result of beam structuring is the formation of a permanent pattern of the refractive index of the film that acts as a cha nnel waveguide trapping a weak Gaussian probe beam coaxial with the main be am. The proposed theoretical model is nonlocal in time and is based on a Sc hrodinger-type nonlinear propagation equation for the main beam and a linea r propagation equation for the probe beam complemented by a rate equation f or the Light-induced decrease of the refractive index. (C) 1999 Elsevier Sc ience B.V. All rights reserved.