NORMAL-INCIDENCE GUIDED-MODE RESONANT GRATING FILTERS - DESIGN AND EXPERIMENTAL DEMONSTRATION

Guided-mode resonant grating filters have numerous applications. Howev er, in weakly modulated gratings designed for use at normal incidence, the filtering resonance of these subwavelength-period devices splits for angles of incidence that are even slightly off normal incidence. S trongly modulated gratings are designed that essentially overcome this practical problem near normal incidence. In addition, these gratings can have, by design, either broad or narrow spectral characteristics. An experimental demonstration (1.5-2.0-mu m wavelength range) of such a normal-incidence guided-mode resonant silicon grating upon a sapphir e substrate is presented. The measured reflection resonance had a FWHM of 67-100 nm for angles of incidence of 0-8 degrees and peak efficien cy of similar to 80 degrees. (C) 1998 Optical Society of America.