Transcending the common perceptions of phase-gradient metasurfaces, metagratings emerge as a new paradigm for wavefront manipulation directly on the desired diffraction order with ultrahigh deflection angles. However, previous metagratings rely on directional scattering caused by multiresonant interference between multiple separate inclusions, of which the high diffrac tion efficiencies are only optimized with limited bandwidth and incident angle tolerance. Here, a kind of asymmetric kissing-dimer metagratings that can achieve broadband high diffraction efficiencies at nearly all incident angles
are proposed and experimentally realized. The building block is formed by touching two titanium dioxide polygon pillars with different geometries, which empowers highly directional scattering patterns in nearly the entire vis ible range. Such kissing-dimer metagratings possess maximum diffraction up to 90% and flat-top bandwidth of about 250 nm. This study provides a trans formative scheme for ultrahigh performance beam steering devices underpin ning various intriguing applications in imaging, sensing, and communication.

DOI: 10.1002/adom.201901389