Circulating Spin Angular Momentum Modes Using a Discretized Metasurface

We propose the spin angular momentum (SAM) space operation of a metasurface, which can realize the circulation of electromagnetic waves with different SAMs. Under a certain cut-off condition to achieve mode selection in a coaxial waveguide, a metasurface can realize the circulation of SAM modes by converting inputs with SAMs of -1, 0, 1 to outputs with SAMs of 0, 1, -1 respectively. To prove the concept, a structure was designed by placing an ideal transmitting metasurface inside a coaxial waveguide. Simulation results show the circulation of three considered SAM modes with near perfect efficiency.