Polarization-controlled bifunctional metasurfaces in transmission and reflection geometries

Recently, gradient metasurfaces, have paved a new direction to the field of metamaterial with many remarkable achievements, including generalized Snell's law [1], new bridge to couple surface wave [2], meta-holograms [3], planar optical devices [4, 5], etc‥ In spite of these great developments, there are some aspects of the metasurfaces needed to be improved. For example, most of the previous systems only operate with the single functionality, which obviously does not satisfy the high integration requirement of the optical devices in modern science and technology. In this paper, we experimentally realized the bifunctional operation based on the polarization-dependent metasurfaces in both reflection and transmission geometry. In the former case, the functionality of the metasurface can be freely switched between focusing and surface wave excitation by rotating the polarization direction of the input linear polarized electromagnetic wave. In the latter case, the metasurface can serve as either a focusing lens or a beam deflector under different polarizations. Compared to the previous works, our device can two distinct functionalities with very high efficiency. The finding may suggest a new avenue to the designs of bifunctional devices.