Reflective and Transmission Metasurfaces for Orbital Angular Momentum Vortex Waves Generation

Metasurfaces are a novel class of two-dimensional (2D) or quasi-two-dimensional (Q2D) artificial electromagnetic surfaces comprised of subwavelength microstructures. These structures allow for precise control over the propagation of electromagnetic waves. Reflective and transmissive metasurfaces, emerging as groundbreaking concepts and techniques, have experienced rapid development in recent years. Meanwhile, vortex waves with orbital angular momentum (OAM) have attracted considerable interest due to their distinctive helical phase distributions. Initially observed in optics, OAM vortex waves have since found applications in microwave and terahertz domains, offering promising opportunities for improving communication modes, expanding channel capacity, and enhancing spectral efficiency. This chapter aims to investigate the characteristics of electromagnetic vortex waves with OAM. Firstly, it offers a comprehensive review of OAM vortex waves in optics. Subsequently, it explores the generation of electromagnetic vortex waves with OAM in the radio frequency range using reflective and transmissive metasurfaces. The combination of metasurfaces and OAM vortex waves holds great potential for manipulating and controlling electromagnetic waves in radio frequency applications. This research contributes to furthering our understanding of these phenomena and opens up new possibilities for advanced communication systems.