Fig. 1. Design strategies for CGH devices based on metasurface. (a) Brief design strategy of meta-holographic devices; (b) Design process of holographic devices using metasurface based on geometric phase as an example

Fig. 2. Static meta-holography. (a) PB phase-modulated 3D on-axis transmission holograms based on gold nanoantennas^[32]; (b) Two amplitude-modulated holograms of photon sieves with set relation^[40]; (c) Complex amplitude modulation is achieved by adjusting the orientation angle and geometric parameters of the cell structure, and the holographic images at the wavelengths of 1.65 μm and 0.94 μm are reconstructed respectively^[42]; (d) THG nonlinear modulated cyan and blue holograms based on C-shaped Si nanoantennas^[43]

Fig. 3. Schematic of meta-holography. (a) Static meta-holography; (b) Multiplexed meta-holography, which means dynamic display can be realized by controlling the fundamental properties of incident light; (c) Active meta-holography, which means metasurface itself can be changed in response to optical, electrical, thermal, or chemical stimuli

Fig. 4. Different methods for wavelength-multiplexed meta-holography to realize color holography. (a) Spatially staggered arrangement^[64]; (b) Multilayer design and adjusted GS algorithm^[68]; (c) Dispersion phase-based metasurface^[70]; (d) Combined with angle multiplexing technology^[73]

Fig. 5. Angle multiplexed and polarization multiplexed meta-holography. (a) Angle-multiplexed meta-holography, which can display different images at 0° and 30° incident angles, respectively^[77]; (b) Combined with nanoprinting and four different images can be projected^[80]; (c) Combine the propagation phase with the geometric phase to realize the multiplexing of LCP and RCP^[86]; (d) Simultaneously record a continuous grayscale nanoprinting image in the near field and project two independent holographic images in the far field^[87]; (e) Three-dimensional vectorial holography with a large field of view (94°) and high diffraction efficiency (78%) based on machine learning inverse design^[92]

Fig. 6. OAM multiplexed, space channel multiplexed and nonreciprocal meta-holography. (a) OAM-multiplexed meta-holography with discrete spatial frequency distribution^[98]; (b) Dielectric multi-momentum meta-transformer in the visible^[100], scale bar: 20 μm; (c) Space channel multiplexed metasurface, which can realize dynamic holographic video display in a way similar to cinematography^[101]; (d) Space channel multiplexed metasurface, which can realize cinematography-inspired dynamic holographic display and display 2²⁸ different frames with structured laser beam^[102]; (e) Space channel selecting metasurface realized by a template^[104]; (f) Nonreciprocal meta-holographic device^[108]

Fig. 7. Diffracted light field multiplexed meta-holography. (a) Diffracted light field multiplexed meta-holography, which can realize dynamic display by changing the incident light field with spatial light modulators^[110]; (b) Cascaded metasurface, which can display different holographic images in the mood of single-layer or multi-layer^[111]; (c) Use the in-plane rotation between two cascaded metasurface to introduce the concept of the rotational multiplexing method and display different images^[112]

Fig. 8. Applications based on multiplexed meta-holography. (a) A polarization-multiplexed holographic device for gas sensing by combining liquid crystal materials and the circular polarization of incident light can be switched under different gas concentrations which leads to holographic image switching between two images^[117]; (b) Code division multiplexed metasurface^[118]; (c) A vectorial holographic device can control the phase information of the holographic image plane to hide or display image information under specific input and output conditions^[119]

Fig. 9. Active meta-holography. (a) Switchable spin Hall effect, vortex beam generation and holography based on GST phase transition properties^[126]; (b) Dynamic metasurface holography based on Mg hydrogenation/dehydrogenation properties^[132]; (c) Dynamic switching display of holographic image based on stretchable PDMS substrate^[135]

Fig. 10. Active meta-holography. (a) Switchable meta-holographic device based on environmentally sensitive MIM structures^[138], scale bar: 40 μm; (b) Electronically controlled digital metasurface for optical projection display^[143]; (c) Refractive index modulation by femtosecond laser pulse reduction of to achieve wide-FOV 3D holograms^[148]

Fig. 11. Micro-nano fabrication technologies for optical metasurfaces (a) Electron beam lithography; (b) Focused ion beam; (c) Photolithography; (d) Plasmonic cavity lithography; (e) Nanoimprint lithography; (f) Two-photon polymerization laser direct writing