Fig. 1. (a) Schematic depiction of the envisioned all-chalcogenide dynamically tunable metasurface filter. The meta-atom composing the metasurface comprises the highly thermally stable Ge25Sb10S65 (GSS) and Ge2Sb2Te5 (GST). (b) Illustration of the meta-atom geometry of the proposed metasurface. The period (Λ) of the unit structure is 940 nm; the protective layer GSS has a height (H) of 345 nm and a radius (R) of 420 nm; and a PCM GST with a thickness (h) of 30 nm and a radius (r) of 410 nm is embedded in the GSS and placed at a distance of 172.5 nm above the substrate.

Fig. 2. (a) Refractive indices (n) and (b) absorption coefficients (k) of amorphous GST (a-GST), crystalline GST (c-GST), and GSS glass.

Fig. 3. (a) Reflectance spectra of the designed metasurface under normal incidence conditions, showcasing the distinct responses when GST is in the amorphous (a-GST) and crystalline (c-GST) states. (b) and (c) Magnetic field distributions corresponding to the magnetic resonance of GST in the amorphous and crystalline states, respectively. (d) and (e) Electric field distributions associated with the electric resonance of GST in the amorphous and crystalline states, respectively.

Fig. 4. Relationships between the positions of (a) a-GST and (b) c-GST within the meta-atom of the designed metasurface and the reflection (R) of the metasurface filter, respectively.

Fig. 5. Relationships between the thicknesses of (a) a-GST and (b) c-GST within the meta-atom of the designed metasurface and the reflection (R) of the metasurface filter, respectively.

Fig. 6. Reflectivity R of the designed metasurface as a function of GST crystallization ratio m.

Fig. 7. Relationship between the incident light polarization and the reflection R of the designed metasurface filter for (a) a-GST and (b) c-GST, respectively.

Fig. 8. Relationship between the incidence of TM waves at different angles and the reflection (R) of the designed metasurface filter for (a) a-GST and (b) c-GST, respectively. Relationship between the incidence of TE waves at different angles and the reflection (R) of the designed metasurface filter for (c) a-GST and (d) c-GST, respectively.

Fig. 9. (a) Illustration of the transversal section of the phase-change metasurface. (b) Schematic representation of the photothermal control scheme for the proposed GST-GSS metasurface consisting of a 5×5 array. RL denotes the radius of the 532 nm top-hat laser beam.

Fig. 10. (a) Power curves depicting the crystallization and amorphization simulation processes of a single unit. (b) Simulated thermal curves of the GST central region of a single unit during the crystallization and amorphization simulation processes.

Fig. 11. (a) Calculated average thermal curves of the GST central temperatures for the 5×5 metasurface during the crystallization and amorphization simulation processes. (b) Top view and (c) side view of the thermal distribution during the metasurface crystallization and amorphization simulation process.

Fig. 12. (a) Simulated thermal curves of a single unit in the crystallization simulation process. (b) Simulated thermal curves of a single unit in the amorphization simulation process. (c) The temperature variation curve for irradiating the GSS meta-atom without GST under the same conditions.