Dielectric metasurfaces in transmission and reflection modes approaching and beyond bandwidth of conventional blazed grating.

Beyond the wave manipulation at a single frequency, efficiency bandwidth control and functional dispersion engineering over metasurfaces are key challenges towards practical applications. Here we propose a type of wideband dielectric metasurfaces made of ultra-thin and layered high-index dielectric patches. The inclusions can be considered as effective material with designable effective refractive index and dispersion. Beam-deflection metasurfaces composed of such inclusions are characterized with the bandwidth approaching and surpassing the limit of conventional blazed gratings in transmission and reflection manners. The bandwidths are more than twice of that in popular single-layer dielectric metasurfaces made of pillar and disk building blocks. In addition, the proposed design benefits from operation over wide range of incident angles and with large tolerance to fabrication errors. More complicated beam manipulation can be fulfilled similarly with great potential for wideband planar optics.