Total multimode reflection at facets of planar high-contrast optical waveguides

Based on rigorous mode expansion simulations, we consider the problem of guided light reflection at rectangular end facets of planar dielectric waveguides. Emphasis is on multimode structures with high refractive index contrast and on configurations that show a high reflectivity. Given the matrix of reflection coefficients for the guided fields, one can compute the maximum power reflectance for an incident mode superposition. While even for a substantial refractive index contrast across the facet the maximum reflected power for a single incoming mode is always moderate, the reflectivity may rise to a level that justifies the attribute total if one considers specific superpositions of at least two guided modes. The paper shows the results of numerical experiments for two series of symmetrical and nonsymmetrical waveguides and identifies conditions on the facet geometry and the exciting field, which are prerequisites for the full reflection effect.