Fig. 1. (a) Structural schematic diagram of symmetric and asymmetric deflectors^[26]; (b) Experimental characterization setup and actual photography of anomalous reflection^[27]

Fig. 2. Off-axis meta-lens. (a) Schematic diagram showing the coordinates of the meta-lens, and the displacement of the focal line along the x′-axis (normal to the focal axis) as a function of wavelength^[28]; (b) Compact spectrometer composed of meta-lens and CMOS camera^[29]; (c) Experimental characterization of the aberration corrected meta-lens and the Berry phase lens^[30]; (d) Schematic diagram of the relationship between spectral range, Spectral resolution and structural parameters^[31]

Fig. 3. (a) Schematic diagram of folded metasurface^[35]; (b) Numerical simulation results of spectral reconstruction algorithm in SLIM system^[36] ; (c) Schematic of an optical architecture for hyperspectral imaging system^[37]; (d) Set up of the dispersion experiment and the splice diagram of experimental results^[38]

Fig. 4. Spectral imaging based on transmission-type metasurface. (a) Compact spectrometer composed of integrated filter array^[44]; (b) Simulated transmission spectra of a group of filters with different nanopillar widths^[46]; (c) Schematic diagram of a hypersurface snapshot spectral imager^[47]; (d) Schematic diagram of generating process of the multispectral filter mosaic^[4]; (e) Block diagram of target detection strategy for unknown source incident power^[48]

Fig. 5. Spectral imaging based on absorption-type metasurface. (a) 3D schematic of the multispectral metamaterial absorber^[61]; (b) Schematic diagram of the hybrid plasmonic− pyroelectric detectors^[63]; (c) Electric field distributions excited at resonant peaks^[63]; (d) Schematic illustration of the multilayer metasurface absorber^[65]

Fig. 6. Spectral imaging based on reflection-type metasurface. (a) Schematic of the guided-mode resonance filter with gradient grating periods^[7]; (b) Molecular fingerprint detection with pixelated dielectric metasurfaces^[68]

Fig. 7. (a) Micro-spectrometer based on photonic-crystal (PC) slabs^[76]; (b) Comparison of reconstructed spectra of photonic crystal filters and novel filters^[88]; (c) Design and fabrication diagram of nanocolumn^[91]; (d) Schematic drawing of the metasurface-based multispectral and polarimetric detection^[92]

Fig. 8. Tuned metasurface. (a) Phase-change metasurface spectral modulator based on GSST^[103]; (b) Cross-sectional view of the MIM structure^[101]; (c) Reflection spectrum and electric field distribution of a-GST and c-GST as dielectric layers^[101]; (d) Schematic representation of the electrically tunable color filter^[105]; (e) Schematic of graphene metasurface modulator^[106]

Fig. 9. Spectral reconstruction algorithm. (a) Schematic diagram of spectral reconstruction system^[82]; (b) Reconstruction results of broadband spectra^[82]; (c) Narrow band spectral reconstruction results based on CS theory^[81]; (d) Design framework for parametric constrained spectral encoders and decoders^[83]; (e) Reconstruction results based on deep learning^[113]

Fig. 10. (a) Molecular fingerprint retrieval and spatial absorption mapping^[68]; (b) Optical characterization of graphene using dielectric metasurface^[66]; (c) Metasurface device diagram for mouse cerebral hemodynamic imaging^[81]

Fig. 11. (a) Spectral measurement results of a real face and other masks^[79]; (b) Operation schematic of the crypto-display^[117]; (c) Demonstration of NIR imaging through the object that is opaque at visible wavelengths^[119]