Numerical procedures for constructing equivalent slab waveguides-an alternative approach to effective-index theory

Standard effective-index methods may fail when properties of a waveguide are cut off. As an alternative, a simple numerical procedure is presented by which an equivalent slab waveguide is similarly substituted for the original two-dimensional refractive-index profile. The technique is demonstrated for a rib waveguide and shown to be in agreement with exact results obtained by other means. It provides an efficient way to replace a two-dimensional transverse distribution of refractive indexes with an equivalent one-dimensional profile. Consistent with the rationale of effective-index theory, it seeks to produce the most reasonable one-dimensional representation of an intrinsically two-dimensional distribution. An equivalent slab formulated in this way should provide a good starting point for subsequent beam propagation calculations involving longitudinally varying structures