SELF-LOCALIZATION AND SPONTANEOUS SYMMETRY-BREAKING OF OPTICAL-FIELDS PROPAGATING IN STRONGLY NONLINEAR CHANNEL WAVE-GUIDES - LIMITATIONS OF THE SCALAR FIELD APPROXIMATION

We examine an application of scalar field theory to the prediction of modal properties of highly localized optical fields that propagate stably along a nonlinear channel waveguide. By comparison with results previously computed with the exact vectorial approach, serious limitations on the validity of the scalar approximation are found in the high-power regime, where nonlinearities are expected to play an essential role in forming the stationary mode. As in the vectorial calculation, a catastrophic transition from a symmetric to an asymmetric mode is confirmed for the channel waveguide with a linear core embedded in a self-focusing nonlinear cladding.