High-order multipoles in all-dielectric metagrating enabling ultralarge-angle light bending with unity efficiency

Abstract: Gradient metasurfaces have been extensively applied in recent years for enabling an unprecedented control of light beam over thin optical components. However, these metasurfaces suffer from low efficiency when it comes to bending light with large angle and high fabrication demand when it requires fine discretion. In this work, we investigate the all-dielectric metagrating based on mie-type resonances interference, allowing extraordinary optical diffraction for beam steering with ultralarge angle. It is found that the coupling inside and among lattice of metagrating can tune the exciting state of electric and magnetic resonances including both fundamental dipoles and high-order multipoles, leading to ideal asymmetrical scattering pattern for redistributing the energy between the diffraction channels at will. The participation of quadrupole and hexapole not only significantly enhance the working efficiency, but also bring distinctive possibilities for wave manipulation which cannot be reached by dipoles. Utilizing a thin array of silicon rods, large-angle negative refraction and reflection are demonstrated with almost unity efficiency under both polarizations. Compared with conventional metasurfaces, such an all-dielectric mategrating has the merits of high flexibility, high efficiency and low fabrication demand. The strong coupling and prosperous interactions among multipoles may behave as a cornerstone for broad range of wavefront control and offer an effective solution for various on-chip optical wave control such as bending, focusing, filtering and sensing.