Terahertz Switchable Vortex Beam Generator Based on Vanadium Dioxide Reflective Metasurface

Vortex beams exhibit significant potential for applications in diverse fields, such as optical communications, particle manipulation, and quantum information, due to the orbital angular momentum (OAM) they carry. While substantial progress has been made in the generation of vortex beams and the control of their wavefronts, further optimization is necessary to enhance the variability of OAM modes and the modulation of focusing. This study presents three tunable vortex beam generators based on vanadium dioxide metasurfaces. By leveraging the insulator-metal phase transition of vanadium dioxide (VO2), 2 ), these metasurfaces can convert incident left- circularly polarized (LCP) light into a deflected vortex beam with adjustable OAM modes, a switchable focused vortex beam, or a focused vortex beam with tunable OAM modes in the terahertz band. Specifically, by varying the angle of the incident light, a vortex beam carrying variable topological charges can be deflected over a range from-34 degrees degrees to 90 degrees. degrees . Vortex beams with a topological charge of 1 enable reversible switching between near- focus (0.85 mm) and far-focus (3.2 mm), demonstrating highly effective tunable focusing capabilities. Additionally, focused vortex generators with switchable topological charges are proposed. Focused vortex beams with a topological charge of-1 are generated in the insulating state, while a topological charge of-2 is observed in the metallic state. These vortex beam generators allow for different phase gradient distributions in the phase transition states, enabling diverse OAM and variable focuses. This research has potential applications in areas such as dynamic imaging and optical communications.