Color filter based on a subwavelength patterned metal grating

TLDR

A subwavelength metal‑film grating color filter was designed with finite‑difference time‑domain simulations and fabricated by electron‑beam direct writing, using a 50‑nm grating height, a dielectric overlay for index matching, and pitches of 340 nm (red) and 260 nm (green). The red filter centered at 680 nm reached 57 % peak transmission, the green at 550 nm 50 %, and the index‑matching overlay raised transmission by ~15 % while merging double bands into a single dominant band, enhancing color selectivity.

Abstract

A color filter incorporating a subwavelength patterned grating in a metal film perforated with a square array of circular apertures on a quartz substrate was accomplished. Its performance was enhanced by applying a dielectric overlay to the grating layer so as to match the refractive indices of the media on either side of it. The device was designed by utilizing the finite-difference time-domain method and implemented by adopting the electron-beam direct-writing technique. Two different devices were fabricated with the structural parameters: the grating height of 50 nm and the pitch of 340 nm for the red color and 260 nm for the green color. For the red color filter the center wavelength was 680 nm and the peak transmission 57%, while for the green color one the center wavelength was 550 nm and the peak transmission 50%. It was confirmed the introduction of the index matching overlay led to an increase of ~15% in the transmission efficiency and helped combine double bands into a single dominant band as well, thereby improving the color selectivity of the filter.