Characteristics of waveguide-grating filters: plane wave and Gaussian beam illumination

Guided-mode resonance refers to sharp resonance effects in planar dielectric-layer diffraction gratings (with dielectric surrounding media) where 100% switching of light energy between reflected and transmitted waves occurs over small parameter ranges. Physically, this is due to coupling of the externally propagating diffracted fields to the modes of the waveguide. This guided-mode resonance phenomenon represents a new fundamental effect suitable for device applications including, static and tunable spectral filters with narrow, controllable linewidth and efficient, low-power switching elements. Using a high spatial frequency dielectric grating may lead to 100% reflective narrow-band spectrally selective mirrors. So far, we have only treated plane-wave resonances ignoring effects of phase curvature which can be the limiting effect in real device applications. Thus, the goal of the present paper is to evaluate the effects of beam divergence and the associated phase curvature on the resonance efficiency of waveguide-grating resonance devices