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In this talk, we present and discuss our recent advances on meta-gratings. Graded metasurfaces, as ultrathin planar arrays of closely-located polarizable inclusions, have attracted significant interest due to their unprecedented control over the flow of light. It was recently shown that metasurfaces based on this approach suffer from fundamental limits on the overall conversion efficiency. In addition, this method typically requires deeply subwavelength fabrication resolution that is imposed by the need for discretization of continuous fastly-varying impedance profiles. To overcome this issue, we have introduced the concept of meta-gratings, formed by periodic arrays of carefully tailored bianisotropic inclusions. We show that the proposed concept enables wavefront engineering with unitary efficiency and significantly lower fabrication demands both in transmission and reflection. Beyond beam-steering, we show metagratings for focusing and lensing, and to impart linear operations on the optical wavefront in momentum space.
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