Fig. 1. Structure of the switchable bifunction polarization converter. (a) Perspective view; (b) top view; (c) side view of the unit cell

Fig. 2. Dielectric constants of BDS at different Fermi energy levels. (a) Real part; (b) imaginary part

Fig. 3. Simulation results when BDS are used as QWP. (a) Reflection coefficient of co-polarization and cross-polarization; (b) phase and phase difference corresponding to reflection coefficient; (c) decomposition diagram of incident wave vector; (d) phase and phase corresponding to reflection coefficient in u-v coordinate system; (e) ellipticity

Fig. 4. Simulation results when BDS are used as HWP. (a) Reflection coefficient and PCR; (b) phase and phase difference corresponding to reflection coefficient in u-v coordinate system

Fig. 5. Current distribution of top resonator and gold film when metasurface are used as QWP. (a) 2.048 THz; (b) 2.693 THz; (c) 3.344 THz

Fig. 6. Current distribution of top resonator and gold film when metasurface are used as HWP. (a) 2.770 THz; (b) 3.495 THz

Fig. 7. Performance of metasurface at different Fermi energy levels. (a) QWP; (b) HWP

Fig. 8. Spectra of the metasurface. (a) Spectra in TE mode when metasurface acts as QWP; (b) spectra in TM mode when metasurface acts as QWP; (c) spectra in TE mode when metasurface acts as HWP; (d) spectra in TM mode when metasurface acts as HWP