Fig. 1. (a) Three-dimentional (3D) schematic of the unit structure composed of a BaF₂ substrate and a GSST brick. (b), (c) 2D schematic of the unit structure, where the rotation angle θ relative to the x-axis is counterclockwise. (d)–(g) Working principle of the GSST metasurfaces for generating tunable vector beams in both amorphous and crystalline states. pol., polarized.

Fig. 2. The transmittance (a) amplitudes and (b) phases of the unit structure as a function of wavelength under x- and y-polarized excitations when GSST is in the amorphous state. Calculated DoLPs and AoLPs as a function of the rotation angle θ at λ = 8.55 µm under (c) LCP and (d) RCP incidences. The polarization states when (e) θ = 0° and (f) θ = 45° at λ = 8.55 µm.

Fig. 3. (a), (b) The transmittance (a) amplitudes and (b) phases of the unit structure as a function of wavelength under x- and y-polarized excitations when GSST is in the crystalline state. (c), (d) Calculated DoLPs and DoCPs as a function of the rotation angle θ at λ = 8.55 µm under (c) LCP and (d) RCP incidences. (e), (f) The polarization states when (e) θ = 0° and (f) 45° at λ = 8.55 µm.

Fig. 4. Performance of the VVB generator with GSST in the amorphous state. Electric field intensity and electric field vector diagrams for (a), (b) LCP incidence and (g, h) RCP light incidence; polarization-resolved (c), (d) far-field intensity and (e), (f) phase distributions under LCP incidence; polarization-resolved (i), (j) far-field intensity and (k), (l) phase distributions under RCP incidence.

Fig. 5. Performance of the second-order vector beam generator with GSST in the crystalline state. Electric field intensity and electric field vector diagrams for (a), (b) x-polarized light incidence and (g), (h) y-polarized light incidence; polarization-resolved (c), (d) far-field intensity and (e), (f) phase distributions under x-polarized light incidence; polarization-resolved (i), (j) far-field intensity and (k), (l) phase distributions under y-polarized light incidence.