Fig. 1: Silicon on sapphire (SOS) visible meta-optics.
From: Full color visible imaging with crystalline silicon meta-optics

a Refractive index and absorption coefficient for crystalline silicon on sapphire for 400–700 nm. b Absolute transmission for SOS compared to a-Si: H and SRN, with values taken from references. c Illustrative comparison of the required pillar height to obtain scatterer with a 2π phase coverage. Here are pillars compared in SOS, with generic pillars with a refractive index of ~2. 5 and 2. d Schematic of nanoscale SOS scatterer with square footprint, defined by period p, height h, and side length x. d Phase delay of square scatterer for wavelengths across the visible range, as a function of the side length x. The colorbar represents the phase delay, in units of 2π. e Picture of a sos meta-optic with aperture size of 5 mm. f Top down SEM image of a section for a meta-optic. g Top-down SEM image of a section of scatterer, highlighting the size control on the nanometer scale. h Angled SEM image of the nanoscale SOS scatterer