Self-localization and spontaneous symmetry breaking of optical fields propagating in strongly nonlinear channel waveguides: 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.