Photon spin hall effect-based ultra-thin transmissive metasurface for efficient generation of OAM waves

Metasurfaces deployed for generating electromagnetic waves that carry orbital angular momentum (OAM) in the transmission mode are generally inefficient in operation. In this paper, we present a method for the design, fabrication, and characterization of an ultra-Thin metasurface which could be used for generating OAM waves at microwave frequencies with high efficiency. We achieve this objective by proposing a novel bilayer subwavelength scatterer having \pi retardation phase between two orthogonal polarizations of an incident circularly polarized (CP) wave that also have high amplitudes. When analyzed our setup using Jones matrices, we find that the scatterer inverts the spin direction of the incident CP wave with high efficiency. Furthermore, the setup provides full phase control with the spatial rotation of the scatterer as per Pancharatnam-Berry Phase Mechanism. To further illustrate the utility of the proposal, a metasurface was designed based on the proposed scatterer and the generation of OAM waves is validated through both simulations and experimental measurements. To further clarify the points, a rigorous analysis for the transmission and conversion efficiencies is presented.