Design and fabrication of guided-mode resonant grating filter with antireflection structured surface

Abstract

We have proposed a new structure of guided-mode resonant grating (GMRG) filter with low sideband reflectance. This GMRG filter consists of a high refractive index thin-film on an antireflection structured (ARS) surface called “moth-eye structure”. This antireflective GMRG filter is valid for reducing reflection of nonresonant light waves in a wide spectral range. This antireflective GMRG filter is valid for reducing reflection of nonresonant light waves in a wide spectral range. The resonant reflection of this new filter was investigated by numerical calculation based on an electromagnetic grating analysis. In the case of an antireflective GMRG filter with aspect ratio 2, the sideband reflectance for nonresonant light waves was lower than 0.5% for TM polarized light in the wide-wavelength range. We have fabricated an antireflective GMRG filter. The triangular grating of fused silica for ARS surface was fabricated by reactive ion etching due to high-density fluorocarbon plasma with resist line patterns and chromium thin-film line patterns as etching masks. The fabricated antireflective GMRG filter was a period of 333 nm and a height of about 666 nm. The thickness of a TiO₂ thin-film deposited on the triangular grating was about 100 nm. Resonant peak was detected at wavelength of 680 nm, and peak intensity was 45%. Moreover, it was found that sideband reflectance was less than 4%.