Metagratings: A novel paradigm for efficient wavefront control

Metasurfaces have recently gained a lot of attention in the context of beam steering, but they are subject to fundamental limitations regarding their efficiency, that cannot be overcome unless we use active or nonlocal materials. Here we show that these limitations can be overcome if we approach the problem of beam steering from a grating perspective. We show that by using metamaterial elements as the building blocks of a periodic lattice we can achieve extreme beam steering with unitary efficiency, if these elements are designed to cancel all the diffraction orders supported by the lattice apart from the one where we want to reroute an incident wave. We call such structures metagratings, in order to highlight the two main aspects of such structures, the grating principle and the metamaterial elements forming it.