Analysis of metallized-grating coupled twin-waveguide structures

In this paper, we present an analysis of grating coupled twin-waveguide str uctures consisting of a semitransparent metal-low-index waveguide on top of a corrugated high-index laser waveguide, A rigorous Floquet analysis of TE modes is performed for trapezoid shaped gratings. Starting from on-resonan t Floquet solutions, me establish a relation to simple coupled-mode equatio ns yielding results, that show excellent agreement with the rigorous Floque t solutions. Grating coupled radiation plays a crucial role in the waveguid e structures under consideration: when phase matching of the guided modes o ccurs, narrow-band resonant suppression of radiation loss with linewidths i n the subnanometer regime can be achieved. The grating geometry has an impo rtant impact on these resonances, which is made evident by various numerica l examples demonstrated in this paper.