Analysis of waveguide gratings: a comparison of the results of Rouard’s method and coupled-mode theory

Recently we introduced a new computational tool for the analysis of waveguide diffraction gratings based on Rouard’s method, a recursive technique used in thin-film coating design. In this paper we compare the reflectivities predicted by Rouard’s method with those found by using the ideal mode expansion of coupled-mode theory for both periodic and aperiodic gratings. We find empirically that the two methods are in excellent agreement, with typical differences in reflectivity of less than 1%.