Resonances of slanted dielectric diffraction gratings in asymmetric waveguide geometry

Abstract

Wood's anomalies are natural phenomena associated with diffraction gratings. The term anomaly refers to a rapid variation of externally observable fields with respect to the wavelength or angle of incidence of the input wave. Hessel and Oliner1 pointed out that there are two types of anomalous effects, the Rayleigh type and the resonance type. Wang et al.2 treated the resonance-type anomaly associated with planar dielectric-layer diffraction gratings. There, the guided-mode resonance characteristics of the evanescent and propagating fields were studied by using the rigorous coupled-wave theory. The present contribution is an extension of the work by Wang et al. The resonances are studied for a generalized geometry allowing grating slant and arbitrary surrounding media (asymmetric waveguide case). For small modulation and thin gratings, the usual eigenvalue equation of the corresponding unmodulated waveguide accurately predicts the locations of the resonances. For increasing modulation or waveguide thickness, numerical results calculated with the rigorous coupled-wave theory are presented to quantify these phenomena with respect to the grating parameters.