Ultra-broadband wide-angle anti-reflection scheme utilizing multi-layer resonant metasurfaces.

Suppressing reflection at the interface separating media with different optical properties has always been an objective, common to many disciplines involving wave phenomena. This task constitutes an even greater challenge for beams exhibiting complex spatiotemporal profiles as broadband (spectral and spatial) operation is required. Here we present a new approach for obtaining broadband antireflection properties by utilizing nanostructure arrays in a multi-layer metasurface configuration with periodicity in the order of a wavelength. As a concrete example, we show the ability to attain ultra-broadband reflection suppression exceeding  -30dB in a Silicon-Air interface, over a bandwidth of ~ 400 nm at telecom wavelengths and an incidence angle of ± 30˚. This method offers several inherent advantages over moth-eye-like approaches as it allows for a more repetitive fabrication process while facilitating a monolithic, single-material antireflection structure. Furthermore, such AR structures can also be realized using additive manufacturing techniques such as 3D printing and Nano-Imprint Lithography.