Fig. 1. Configuration of the EIT metasurface. (a) Schematic of the all-optical, nonvolatile, chalcogenide metamaterial induced EIT switch: single ns laser pulse transits a 35-nm-thick GST225 film, backward and forward between AM and CR on an area covering 510,000 antennae. (b) A representation of the resonator. The geometrical parameters are: l1=380nm, l2=550nm, w=220nm, d=120nm, and p=700nm, respectively; the thicknesses of the top Au resonator and GST225 dielectric layer are TAu=35nm and TGST=35nm, respectively. The SEM images of the 5×7 resonators section of the fabricated metasurface (c) before crystallizing and (d) after crystallizing the GST225 dielectric film hybridized with the metasurface. Scale bar: 2μm.

Fig. 2. Sequential treatment for the reversible phase transition. (a) Scheme of the reversible phase transition of the GST225 film hybridized with an EIT metasurface: AD-AM GST225 is first annealed above 180°C to change to CR GST225 using a hot plate. A single ns laser pulse (5 ns, 24mJ/cm2) is triggered to heat the CR GST225 film above 600°C that re-amorphizes the CR GST225. Subsequent quenching results in the MQ-AM GST225. To recrystallise the MQ-AM GST225, for which a temperature above 180°C but below 600°C is required, a single-ns laser pulse with a lower energy (5 ns, 14mJ/cm2) is taken. (b) Visible–NIR complex refractive index of 35-nm-thick GST225 film at the structural states of the AD-AM (red line), CR (blue line), MQ-AM (orange line), and R-CR (green line), where the refractive index is measured using an ellipsometer over a spectral range of 1000 to 2400 nm.

Fig. 3. Experimental realization of reversibly tunable EIT and the comparison with theory and simulation. (a) The FTIR measurement of the normalized transmittance spectra, (b) theoretical fitted transmittance spectra, and (c) numerical simulated transmittance spectra of the phase change metasurface with the different structural states of AD-AM, CR, MQ-AM, and R-CR.

Fig. 4. Bright and dark modes in EIT. The FDTD simulated spectra and E-field distributions for (a) the VCW resonators array with the AM-GST225 film at λ=2021nm, (b) the HCW resonators array with the AM-GST225 film at λ=1565nm, (c) the metasurface with the AM-GST225 film at λ=1811nm, and (d) the metasurface with the CR-GST225 film at λ=2161nm.

Fig. 5. The ng for the different structural states of the GST225.

Fig. 6. (a)–(c) Measured transmittance spectra of the phase change metasurface for 30 switching times. (d) The values of resonance peaks for AM (indicated by red dots) and CR (indicated by blue dots) states with 30 transition times.