Fig. 1. Metasurface unit. (a) Top view; (b) side view; (c) VO₂ phase change process

Fig. 2. Magnitude and phase of reflection at incidence of x and y polarized waves under different states of VO₂. (a) Insulated state; (b) metallic state

Fig. 3. Reflection amplitude and reflection phase of VO₂ in insulated state and metallic state when RCP wave is incident perpendicularly to coding metasurface unit. (a) Reflection amplitude and (b) reflection phase when VO₂ is in insulated state; (c) reflection amplitude and (d) reflection phase when VO₂ is in metallic state

Fig. 4. Coding sequence corresponding to vortex beam with l=1

Fig. 5. Far-field beams of vortex waves at different frequencies for different states of VO₂. (a)(d) VO₂ is in an insulated state at 1.2 THz; (b)(e) VO₂ is in metallic state at 0.88 THz; (c)(f) VO₂ is in metallic state at 1.4 THz

Fig. 6. Coding metasurface with random coding sequence

Fig. 7. Comparison of metasurface far-field pattern with metal plates in different states of VO₂._{(a) Far-field pattern and (b) comparison with metal plates for VO2 in insulated state of 1.2 THz metasurface; (c) far-field pattern and (d) comparison with metal plates for VO2 in metallic state of 0.88 THz metasurface; (e) far-field pattern and (f) comparison with metal plates for VO2 in metallic state of 1.4 THz metasurface}

Fig. 8. Vortex beams with l=1. Far-field patterns at (a) 1.17 THz and (b) 1.37 THz; phases at (c) 1.17 THz and (d) 1.37 THz

Fig. 9. Far-field patterns. (a) 1.17 THz; (b) 1.37 THz

Fig. 10. Vortex beams with l = 1. Far-field patterns at (a) 0.87 THz, (b) 0.92 THz, (c) 1.5 THz, and (d) 1.6 THz; phases at (e) 0.87 THz, (f) 0.92 THz, (g) 1.5 THz, and (h) 1.6 THz

Fig. 11. Far-field patterns. (a) 0.87 THz; (b) 0.92 THz; (c) 1.5 THz; (d) 1.6 THz