Fig. 1. Schematic comparison of the optical functions of various types of metasurfaces. (a) Schematic diagram illustrating the transmission characteristics on both sides of a traditional transmissive metasurface (Ff =Fb). (b) Schematic diagram illustrating the transmission characteristics on both sides of an asymmetric Janus metasurface (Ff ≠Fb). (c) Schematic diagram illustrating the transmission characteristics on both sides of a reconfigurable asymmetric Janus metasurface.

Fig. 2. Complex refractive indices, n, and the extinction coefficients, k, of A-Sb2S3 and C-Sb2S3 from 400 to 700 nm.

Fig. 3. Scheme for switching an asymmetric hologram based on a nonvolatile reconfigurable Janus metasurface. When LCP white light is incident onto the metasurface, either in a forward or backward direction, four independent holographic images are reconstructed under different states. (b) Left, three different optical decoding keys; right, optical characterization of the nonvolatile reconfigurable Janus metasurface.

Fig. 4. (a) Detailed flow chart of the reconfigurable asymmetric transmission metasurface design. (b) Optimization process using the modified GS algorithm.

Fig. 5. Structural design and optical properties of meta-atoms. (a) 3D view, side view, and top view of the meta-atom. (b) The transmissivity spectra of cross-polarization conversion are simulated at different levels of crystallization. (c) Cross-polarization transmission and phase variation are simulated at different crystallization levels with varying orientation angles. (d) The function of DE with L and W at the corresponding wavelengths is given for different levels of crystallization. (e) The structural colors in the CIE 1931 chromaticity diagram were calculated by simulating the response of transmission spectra at different levels of crystallization. (f) The beam deflection and deflection angle of LCP light are simulated for both forward and backward incidences.

Fig. 6. (a) Diagram of the entire reconfigurable asymmetrical transmission metasurface configuration with top view, zoomed view, and angled view. (b) The flow chart of the image is reconstructed using different wavelengths of LCP light at various levels of crystallinity.

Fig. 7. Co-polarization and cross-polarization transmission efficiency of the reconfigurable Janus metasurface sample with different crystallinity. (a) A-Sb2S3. (b) C-Sb2S3.

Fig. 8. (a) Simulation results of a single wavelength LCP incident light with a wavelength of 550 nm (650 nm) when the metasurface is in an amorphous (crystalline) state. (b) Complex refractive index curve of the semi-crystalline Sb2S3. (c) Cross-polarization conversion efficiency of meta-atoms in a semi-crystalline state. (d) Simulation results of dual-wavelength LCP incident light at 550 nm and 650 nm when the metasurface is in a semi-crystalline state.

Fig. 9. Manufacturing tolerances of the reconfigurable Janus metasurface. (a) Variation of the simulated cross-polarization transmission spectra of A-Sb2S3 nanorods with different lengths, widths, and thicknesses. (b) Variation of the simulated cross-polarization transmission spectra of C-Sb2S3 nanorods with different lengths, widths, and thicknesses.

Fig. 10. Numerical analysis of unit structures for reconfigurable asymmetric transmittance metasurfaces. The scanning results are separately calculated for different wavelengths, levels of crystallinity, and polarization states.

Fig. 11. Design process of the PSO algorithm for optimizing the size of the nanorods.

Fig. 12. Potential manufacturing steps for the reconfigurable Janus metasurface.

Fig. 13. Potential experimental setup for measuring the encrypted holographic images.