Effects of the Film Index on the Fields of Nonlinear-Cladding Optical Waveguides With Butt-Coupled Linear Waveguides

Effects of the film index of nonlinear-cladding optical waveguides on the evolution of fields at medium power levels are investigated numerically. The analysis method is based on mode matching of local normal modes of bounded waveguides. For waveguides with a film whose refractive index is greater than or nearly equal to the linear part of the index of the nonlinear cladding, the path of a beam winds between the film and the nonlinear cladding or in the film. In the case of a film index that is to some extent less than the linear part index of the nonlinear cladding, a beam is emitted to the nonlinear cladding, i.e., spatial soliton emission occurs. The lateral shift of a butt-coupled linear waveguide toward the substrate makes a beam emit to the nonlinear cladding with increased angles. Saturation and linear absorption weakens the winding of a path or decreases the angle of emission.