Variable optical reflectance of a self-supported Si grating

Variable reflectance of a self-supported Si grating mirror is reported. A grating suspended in air consisted of an array of 300 nm wide, 300 nm thick, and 20 μm long beams. The period of the grating was varied with an electrostatic microactuator from 600 to 720 nm. A broadband reflection in the wavelength longer than the grating period was observed, which was caused by a resonant interference of the light wave propagating along the grating similar to the guided-mode resonant gratings. Increasing the period of the grating with a microactuator, the reflection spectrum changed. The results were explained by the theoretical calculations based on rigorous coupled-wave analysis.