Bifunctional metasurface for polarization transformation and vortex generation

Metasurface, as an innovative 2D material, is promoting the technological development of optical control through its extraordinary capacity to precisely manipulate electromagnetic wavefront. We introduce a bilayer metasurface utilizing vanadium dioxide (VO2), which has the characteristic of a reversible insulator-to-metal transition. This metasurface utilizes the mutual interference of a diatomic structure to induce phase delay, enabling the transformation of an arbitrary polarized wave into a specified polarization. Leveraging propagation and geometric phases, it is designed to generate anomalously reflected vortex beams. Furthermore, by controlling the temperature, this approach enables selective switching of incident polarization between linear and circular states, as well as independent control over vortex beams. Specifically, when the temperature exceeds 68°C, the electromagnetic wave is modulated by VO2 patches. Utilizing the propagation phase, the y-polarized reflection port produces a vortex beam carrying topological charge (TC) l=1, exhibiting an anomalous reflection at 30 deg. As the temperature is below 68°C, the gold patch array modulates the incident wave. Leveraging the geometric phase, the metasurface generates an anomalous vortex beam possessing TC l=−2 and anomalous reflection at −30 deg in the right-handed circularly polarized reflection channel. This innovative metasurface opens up possibilities for reconfigurable optical devices and dynamic vortex control, holding great promise for applications in optical communication and information processing.