All-optical controlled ternary encoding polarization THz modulator-based on a vanadium dioxide-metal bilayer reconfigurable metasurface.

Terahertz (THz) polarization modulators play a critical role in application-oriented terahertz wireless communication. Currently, the highly efficient multifunctional polarization state modulator-based optical excitation continues to be a challenge due to limitations in manipulation methods. In this study, we proposed a vanadium dioxide (VO₂)-metal hybrid bilayer metasurface. By independently manipulating the insulator-to-metal transition of VO₂ bars on both surfaces under two pump excitations, the metadevice can freely switch between left-handed circular polarization, right-handed circular polarization, and linear polarization states at a resonance frequency. A ternary encoding for the output polarization states was proposed. Furthermore, an equivalent circuit model was also established to demonstrate its physical mechanism of resonances. The results not only provide what we believe to be a novel method to design multifunction metadevices but also promote the development of polarization modulation technology in terahertz communications.