Six-Mode Orbital Angular Momentum Generator Enabled by Helicity-Assisted Full-Space Metasurface with Flexible Manipulation of Phase, Polarization, and Spatial Information

Abstract

Vortex beam carrying orbital angular momentum (OAM) has been experiencing a research upsurge attributed to its excellent communication capability, which also boosts the development of the OAM technology and promotes the application of the OAM generator. However, most of the existing designs of the OAM generators can only produce a small number of diverse OAM modes, and restrict the channel capacity of single OAM generator. Herein, an appealing strategy of six-mode OAM generator based on helicity-assisted full-space metasurface is proposed to generate up to six diverse OAM modes by altering the polarization state, illumination region, and incidence direction of incident waves. Significantly, the designed OAM generator has high communication security because of its great information entropy, and the generated OAM modes possess the characteristics of high purity and low crosstalk which result from the orthogonal polarization states and unequal deflection angles of produced vortex beams. A proof-of-concept prototype is constructed to corroborate the validity of our methodology, and the results of simulations and experiments are in excellent agreement with theoretical predictions. This fire-new OAM generator will possess a promising application prospect in communication systems, and may also provide an efficacious method to design multifunctional devices.