Dark spatial solitons in photopolymer films for optical interconnections

Abstract

We demonstrate theoretically and experimentally that an initially Gaussian red light beam sent through a ?step phase mask and launched 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 the Kerr-type time-delayed nonlinearity associated with the mechanism of up-converted photobleaching of the dye-doped polymer. The proposed theoretical model is nonlocal in time and is based on the Shrodinger-type nonlinear equation for the amplitude of the propagating beam complemented by the rate equation for the light-induced decrease of the refractive index. The result of the structuring of the beam is the formation of a permanent pattern of the refractive index of the film that acts as a channel waveguide, trapping a weak Gaussian probe beam close to it. The probe beam can propagate along or against the soliton. We also demonstrate the tolerance of trapping to a possible shift or tilt of the probe beam with respect to the soliton. This makes the proposed approach potentially useful for interconnections between individual fibers, fiber ribbons, bundles, and multicore fibers as well as between fibers and planar integrated optical devices.