Active Switching Between Absorption and Polarization Conversion Enabled with VO2-Based Reconfigurable Terahertz Metasurfaces.

Terahertz (THz) metasurfaces have drawn considerable research interest, owing to their compelling potential in sensing, imaging, and wireless communication. However, most existing designs are constrained to a single predefined function, severely hindering their practical applicability in dynamic or multifunctional scenarios. Herein, we present a reconfigurable THz metasurface that enables on-demand functional transformation by harnessing the phase transition characteristics of vanadium dioxide (VO2). The designed unit cell adopts a six-layer stacked configuration, sequentially comprising a VO2 square ring, a first polyimide (PI) dielectric spacer, an elliptical gold patch, an intermediate VO2 thin film, a second PI dielectric spacer, and a gold ground plane. When VO2 is in its metallic phase, the metasurface operates as a metal-insulator-metal (MIM) absorber, achieving over 90% absorption in the frequency range of 1.01-1.91 THz. In the insulating state, it acts as a polarization converter, enabling efficient linear-to-circular polarization conversion (PC) with an axial ratio (AR) below 3 dB from 1.82 to 2.21 THz under linearly polarized (LP) incidence. Moreover, the metasurface exhibits robust performance under varying incident angles and different polarization conditions. Collectively, this design offers a flexible and reconfigurable platform for advanced THz devices, laying a solid foundation for THz communication, intelligent sensing, and imaging systems.