Fig. 1. Schematic of metasurface-based multi-dimensional optical information encryption

Fig. 2. Metasurface-based optical information encryption with single dimensional for single pure input. (a) Wavelength-dimensional optical encryption based on spatial multiplexing^[50]; (b) optical encryption based on angle-of-incidence dimensional multiplexing^[53]; (c) four-channel optical encryption based on angle-of-incidence dimension^[54]; (d) optical encryption scheme with left and right circular polarization^[36]; (e) realizing 11 polarization multiplexing channels by introducing noise into Jones matrix^[37]

Fig. 3. Metasurface-based multidimensional optical information encryption at pure input. (a) Achieving orbital angular momentum hologram based on vortex light combined with space and phase dimensions^[43]; (b) two independent holographic images with input combining wavelength and polarization dimensions^[59]; (c) optical encryption based on coherent pixel design realized by combining wavelength, polarization, and incident angle dimensions at input^[55]

Fig. 4. Metasurface-based optical information encryption with pure single output. (a) Information hidden in specific single linearly polarized light^[60]; (b) two images hidden in orthogonal polarization states^[61]; (c) two images hidden in non-orthogonal linearly polarized states^[62]; (d) optical encryption of multiple images with different observation angles based on large-scale grating pixel structures^[65]; (e) optical encryption with large-scale observation angle multiplexing based on metasurface^[66]; (f) optical encryption with diffraction distance dimension^[67]; (g) stereoscopic Jones matrix holography ^[68]

Fig. 5. Metasurface-based optical information encryption with polarization dimension at both input and output terminals. (a) Holographic encryption based on geometric phase and spatial multiplexing^[74]; (b) three-channel holographic encryption realized by introducing phase difference between two circular polarization states of incident light as additional degree of freedom^[38]; (c) independent phase control achieved under arbitrary orthogonal polarization states based on geometric and propagation phases^[39]; (d) optical encryption of grayscale and binary images based on continuous and degenerate output under linear polarization states of anisotropic unit structure^[41]; (e) optical encryption based on third hybrid channel image formed under different incident and outgoing linear polarization angles^[76]

Fig. 6. Metasurface-based optical information encryption with polarization dimension at input terminal and multi-dimension at output terminal. (a) Two-channel encryption with left and right rotation polarization^[77]; (b) three-channel linear polarization encryption based on highest six degree-of-freedom Jones matrix of planar structure^[78]; (c) four-channel linear polarization encryption based on highest eight degree-of-freedom Jones matrix of double-layer structure^[79]; (d) optical information encryption of holographic images combining with three dimensions of polarization, diffraction distance, and observation angle at output terminal^[80]

Fig. 7. Metasurface-based optical information encryption with wavelength dimension at input terminal and other dimensions at output terminal. (a) Based on nanostructure color filter mechanism^[82]; (b) based on mechanism that nanostructures with different sizes have different resonance diffraction under different wavelengths^[83]; (c) full-color display with arbitrary brightness, saturation, and hue based on three primary colors mixing theory^[84]; (d) three-wavelength channel holographic optical encryption with linearly polarized output varying in space^[85]; (e) two-wavelength channel optical encryption of nanoprinting images with different linearly polarized output^[86]

Fig. 8. Metasurface-based optical information encryption with incident-angle dimension at input terminal and diffraction-distance dimension at output terminal^[87-88]. (a) Angle-multiplexed encryption by building structured database of angle-encoded responses; (b) encoding encryption for different incident angles by using angular illumination to change surface plasma resonance and Fabry-Perot nanocavity resonance

Fig. 9. Metasurface-based optical information encryption with multi-dimension at input terminal and other dimensions at output terminal. (a) Optical information encryption with polarization dimension at output terminal and dual dimensions of incident angle and polarization at input terminal^[89]; (b) optical encryption based on structural spatial multiplexing design and circular polarization state^[90]; (c) optical encryption of circular polarization state under non-multiplexing basic unit constructed based on single nanostructured pixel^[52]; (d) optical encryption of linear polarization state based on neural network^[91]. (e) optical encryption with three dimensions of vortex light (phase and spatial) and polarization at input terminal and linear polarization state dimension at output terminal^[92]; (f) optical encryption with three dimensions of vortex light (phase and spatial) and polarization at input terminal and diffraction distance dimension at output terminal^[46]