Resonant excitation analysis of sub-wavelength dielectric grating

A weakly modulated dielectric grating is equivalent to a planar waveguide. As the high-order spatial sub-waves couple with the leaky mode of the grating, guided-mode resonance (GMR) occurs. In this paper, the resonance positions of a weakly modulated dielectric grating are studied based on the eigenvalue equation of a planar waveguide, and the results agree with the rigorous coupled-wave analysis (RCWA) very well. This shows that double reflection peaks at normal incidence can be realized and the reasons are given in detail. The reason that GMR is sensitive to the incident angle and the grating period is also discussed. GMR filters with good filtering features can be realized by using the thin film effect.