Multifunctional vortex fields manipulation enabled based on vanadium dioxide metasurfaces

Abstract

Vanadium dioxide (VO₂), a prototypical phase-change material, endows terahertz waves with dynamic tunability through its insulator–metal transition. Here we demonstrate a reconfigurable metasurface that exploits VO₂’s dramatic optical switching capability. Based on VO₂, we designed a reflective metasurface which possesses switchable characteristics and can realize several functions including generation of vortex beams, split vortex beams, split vortex beams with focused orbital angular momentum (FOAM), and multi-channel FOAM. Specifically, the paper discusses vortex beams with topological charges l = 1 and l = 2, phase distributions for two-way and four-way splitting, as well as split vortex beams with l = 2, which enhance the capacity for information transmission. A high-purity FOAM function with a focal length of 6000 μm is achieved at a frequency of 0.39 THz. Finally, by combining the FOAM metasurface with split-phase superposition, multi-channel FOAM beams is successfully realized. When linearly polarized waves (LP) are incident on the split FOAM metasurface, the far-field amplitude exhibits four energy channels. In the circumstance of left circularly polarized (LCP) and right circularly polarized (RCP) waves being incident separately, the phase amplitude distribution is oriented towards the negative y-axis and the positive y-axis, respectively, thereby reflecting the transmission of wave in disparate directions. Furthermore, when VO₂ switches to dielectric state, the reflection behavior of the metasurface transitions to specular reflection. The novelty of our approach lies in the dynamic and multifunctional integration of these distinct manipulation capabilities onto a single, reconfigurable platform. By harnessing the phase transition of VO₂, we demonstrate on-demand switching among the operational modes—an advance beyond conventional static metasurfaces. Vortex beams, split vortex beams, FOAM effects, and split FOAM provide diverse means for light-field control and open new possibilities for designing highly tunable, precisely controlled optical devices.