Analysis of a Novel Grating-Assisted Directional Coupler by Using the Normal Mode and Coupled Mode Analyses

Abstract

We present a novel structure of the directional coupler which consists of two non-identical waveguides, with a periodic refractive index perturbation along the direction of propagation. We have compared the coupling characteristics obtained by using the approximate coupled mode analysis and the exact normal mode analysis for the grating-assisted directional coupler. We find that, for the proposed structure, using the modes of the isolated waveguides in the coupled mode theory does not give accurate results, and one should apply the normal mode analysis to obtain the coupling characteristics.