Analysis of forward wide-angle light propagation in semiconductor rib waveguides and integrated-optic structures

The authors analyse longitudinally varying semiconductor rib waveguides with a new nonparaxial wide-angle equation for unidirectional light propagation. They further develop a solution method involving multiplication of the incoming electric field by a series of unitary operators which are evaluated by split-step fast Fourier transform and finite difference techniques. In the test case of a strongly guiding rib waveguide Y-junction, the estimated losses nearly coincide with those of standard Fresnel equation procedures. They also present a numerical analysis of an integrated-optic lens, demonstrating significant errors in previous results. Finally, they explicitly illustrate the increased accuracy of their new method in comparison to the Fresnel equation for a highly nonparaxial Gaussian beam.