Dispersion Engineered Nonlocal Metasurfaces with Customizable Wavefront-Selectivity

We propose and demonstrate nonlocal metasurfaces with wavefront-selective customizable features. In particular, we engineer in extreme ways the modal dispersion of metasurfaces, to go from positive to negative curvature across a flat dispersion regime. This result opens a new degree of freedom to selectively control metasurface responses, added to the already rich opportunities of nonlocal metasurfaces, such as frequency and polarization selectivity, as well as unitary-efficiency wavefront manipulation. We achieve customizable wavefront-selectivity by adding metallic via walls into bilayer nonlocal metasurfaces, which control the lateral energy transfer inside the metasurface while preserving the desired nonlocal properties imprinted in the bilayer. Based on these principles, we demonstrate highly-efficient wavefront-selective and wavefront-independent anomalous reflection and focusing, combined with frequency and polarization selectivity.