Modal conversion in a gradient-index channel waveguide due to boundary perturbations

The effect of boundary perturbations on channel waveguides has been calculated following the effective-index method. As required by this approach, the index perturbations are assumed separable-a form describing defects expected using planar waveguide fabrication techniques. For sinusoidal perturbations, coupling occurs to, at most, one other guided mode and to a small band of radiation modes. As in the planar case, losses at step-index boundaries are greater than those at graded-index boundaries.