Designing Si sphere metagratings: From perfect reflection to large-angle diffraction

A thorough theoretical study of the optical properties of periodic Si nanosphere arrays is undertaken, placing particular emphasis on the synergy between electric and magnetic Mie resonances, which occur in high-refractive-index nanoparticles and can lead to a rich variety of phenomena ranging from perfect reflection to controlled diffraction. By means of systematic calculations using the layer-multiple-scattering method that we properly extended so as to describe periodic arrays with many scatterers per unit cell, in conjunction with finite-element simulations, we optimized surfaces of Si nanospheres that efficiently channel the transmitted light into a single, first-order diffraction beam, following simple design rules based on physical insight. Our results provide compelling evidence that Huygens' metasurfaces consisting of simple Si nanosphere dimer lattices constitute a promising platform for large-angle unidirectional deflection of transmitted light in the visible, at wavelengths shorter than the diffraction edge of the lattice.