Guided waves in graded-index planar waveguides with nonlinear cover medium

Dispersion relations for TE modes in a planar exponentially graded-index waveguide with self-focusing nonlinear cover material have been solved numerically. It is shown that the threshold power required to pull the field maximum out of the film region into the cover is lower compared with that for the step-index waveguide and agrees well with the experimental results. Empirical relations to calculate the corresponding minimum film thickness and the minimum threshold power are given for the lowest-order mode.