Flat metasurfaces to collimate electromagnetic waves with high efficiency.

Directional beaming of electromagnetic waves passing through a subwavelength aperture has attracted considerable interests in photonics, but the traditional approach of utilizing gratings to directionally couple surface waves (SWs) to a desired far-field direction faces the low-efficiency issue owing to high-order diffractions. Here we experimentally demonstrate that directional beaming of light can be realized with very high efficiencies, in …