Highly reflective and high-$Q$ thin resonant subwavelength gratings

We theoretically investigate the design of thin subwavelength gratings possessing high-reflectivity and high-$Q$ resonances when illuminated at normal incidence by a Gaussian beam. We compare the performances of single-period and dual-period rectangular gratings using Finite Element Method-based optimization and predict one to two orders of magnitude improvement in their transmission loss-linewidth product, which is the relevant figure of merit for e.g. resonant mirror-based microcavity applications.