Demonstration of Orbital Angular Momentum Multiplexing and Demultiplexing Based on a Metasurface in the Terahertz Band

Abstract

Orbital angular momentum of light (OAM) is attracting increasing attention in conjunction with the continuing development of high-speed optical communications. The unlimited nature of OAM allows its multiple degrees of freedom to be used in communications applications. In the OAM multiplexing technique, different OAMs provide independent channels to carry and deliver different data. An OAM multiplexing scheme in the terahertz (THz) band based on use of a single-layer metasurface is demonstrated numerically and experimentally in this work. The designed structure generates four focused phase vortex beams that have different topological charges under illumination by a Gaussian beam, which means that OAM multiplexing with four channels is realized. When an individual vortex beam is used as the incident light, only one channel is identified and extracted as a focal spot; that is, demultiplexing of the OAM signal is achieved. The structure has subwavelength-level thickness, which enriches the number of potential approaches available for the miniaturization and integration of THz communication systems. The performance of the designed OAM multiplexing and demultiplexing device shows excellent agreement between the theoretical predictions and experimental results, thus indicating that this device is suitable for ultrahigh-speed THz communications.