Ultrathin metasurface based on phase discontinuity with maximal cross-polarization efficiency

An ultrathin flat metasurface experimentally realizing bi-functional microwave manipulation has been demonstrated to be able to approach the theoretical limit of cross-polarization (cross-pol) conversion efficiency of the transmission. With the excitation of a localized waveguide mode, an abrupt helicity-dependent phase change is introduced to the transmission and can be engineered by assembling the spatial orientation of each Pancharatnam-Berry phase element. By realizing a constant phase gradient, an anomalous refraction is unanimously demonstrated under circular polarized incident wave. Besides, due to the helicity-dependent phase modification, we also demonstrate an ultra-thin metalens with bi-functionality. By controlling the handedness of the incident wave, converging and diverging functions are interchangeable with the same flat lens. The proposed metalens has only one single layer as thin as 0.001λ, which massively reduces the thickness of the microwave lens along the wave propagation direction. With the great improvements in efficiency and thickness reduction, our design provides a promising approach to miniaturize, planarize and integrate multiple microwave components.