Reciprocal asymmetric transmission in self-shadowed metallized gratings

Abstract

A single oblique metallization step gives conventional gratings one-sided silver decoration, established by electron microscopy and elemental mapping. Opposite-face reversal measurements yield finite-aperture red/green/blue transmission ratios up to 1.74 for a 1-$\mu$m grating and 1.5-1.8 for a 30-$\mu$m grating, with reference-normalized transmittances for the latter. Flat-side coating and reduced silver dose give ratios near unity. Maxwell calculations on self-shadowed growth profiles reproduce the directional sign qualitatively and attribute the contrast to diffraction-channel redistribution. The structure remains reciprocal, including its normal-incidence zeroth-order transmission. These results establish directional metallization as a route to direction-selective optical transmission without multilayer alignment or overlay lithography.