Fig. 1. (Color online) Working principle and the schematic of the proposed tunable metasurface. (a) The schematic of the metasurfaces. The left and right figures respectively illustrate the reflection and transmission colors of the metasurface in the amorphous and crystalline states under TM polarization light. (b) The single unit of the device, consisting of elliptical column Sb₂S₃ and CF₂ as substrate. R_x and R_y represent the major and minor axes of the cylindrical structure respectively, while T_x and T_y are the periodicity of the single unit in the two directions. Additionally, t_pcm corresponds to the thickness of the phase change material. (c) Refractive index (blue) and the absorption coefficient (red) of amorphous Sb₂S₃ (solid line) and crystalline Sb₂S₃ (dash line) in wavelength between 400 and 800 nm.

Fig. 2. (Color online) The numerical simulation with R_y changing from 10 to 90 nm (from bottom to top). (a), (b) The reflection spectra of the device in amorphous (a) and crystalline state (b) respectively in TM polarization mode. Panel (c) shows Δλ when the PCMs change from amorphous to crystalline. (d), (e) The reflection spectra of the device in amorphous (d) and crystalline state (e) respectively in TE polarization mode. (f) The CIE1931 plot numerically calculated structural color palettes of amorphous (green) and crystalline (red) states under TM (stars) and TE (circles) polarized wave.

Fig. 3. (Color online) The numerical simulation with R_x changing from 90 to 170 nm (from bottom to top). (a), (b) The reflection spectra of the device in amorphous (a) and crystalline state (b) respectively in TM polarization mode. Panel (c) shows Δλ when the PCM change from amorphous to crystalline. (d), (e) The reflection spectra of the device in amorphous (d) and crystalline state (e) respectively in TE polarization mode. (f) The CIE1931 plot numerically calculated structural color palettes of amorphous (green) and crystalline (red) state under TM (stars) and TE (circles) polarized wave.

Fig. 4. (Color online) The numerical simulation with T_x and T_y changing from 300 to 400 nm (from bottom to top). (a), (b) The reflection (a) and transmission (b) spectra of the metasurface in amorphous with changing T_y in TM polarization mode. (c) The CIE1931 plot numerically calculated structural color palettes of reflection (green) and transmission (red). The reflection (d) and transmission (e) spectra of the metasurface in amorphous with changing T_x in TM polarization mode. (f) The CIE1931 plot numerically calculated structural color palettes of reflection (green) and transmission (red).

Fig. 5. (Color online) The electromagnetic multipole decomposition of reflection spectra in TM Mode with fixed periodicity T_x = T_y = 350 nm and t_pcm = 120 nm. Different results of three structure geometry in atmosphere (a), (b), (c) and crystalline (d), their structural parameters are (a), (d) R_x/R_y of 130/30 nm, (b) R_x/R_y of 130/60 nm, (c) R_x/R_y of 170/30 nm.

Fig. 6. (Color online) The electromagnetic simulation of single unit. Panel (a) shows the single unit whose structural parameters are R_x/R_y/T_x/T_y/t_pcm of 130/30/350/350/120 nm. (b) Reflection spectra of the metasurfaces under TM (left) and TE (right) polarized waves. (c), (d) Electromagnetic field distributions of electric dipole mode and magnetic dipole mode in an amorphous and crystalline state in TE and TM polarization mode. Here the wavelength is 561.5 nm.