Polarization-independent quadri-channel vortex beam generator based on transmissive coding metasurface

In the 1990s, it was recognized that light beams carrying orbital angular momentum (OAM) have benefited applications ranging from optical manipulation to quantum information processing. In recent years, attention has been directed towards the opportunities for communication systems due to the inspiring application potential in both the optical and microwave fields. In this paper, a polarization-independent quadri-channel vortex beam generator based on transmissive metasurface is proposed that can achieve selectivity of polarization, 2-bit OAM modes and spatial distribution in the quadri-channel simultaneously. The transmissive metasurface consists of four metallic layers and three dielectric layers and is designed, fabricated, and experimentally demonstrated to generate multi-mode and dual-polarization OAM vortex beams at 10.0 GHz. Orthogonal polarization and 2-bit information are carried by OAM modes +1, −1 + 2 and −2 and a different phase gradient is superimposed at each channel to realize beam steering, ensuring the accuracy and integrity of the information. The simulation and experimental results verify that the vortex beams with different OAM modes in dual polarizations can be flexibly generated by using transmissive metasurfaces. The proposed method and metasurface pave a way to add extra channels to create an additional set of data carriers for space-division multiplexing (SDM).