Fig. 1. Dielectric grating at different scales. (a) Diffraction gratings; (b) Resonant (subwavelength) gratings; (c) Equivalent dielectric films

Fig. 2. Proposal of metagratings^[7]

Fig. 3. Subwavelength gratings and metagratings at different wavelengths^[17-27]

Fig. 4. Narrow-frequency sharp-angular transmission filter structures and the spectrum using cascaded metagratings^[28]

Fig. 5. Analytical theory of optical gratings: mode expansion, resonant and interference. (a) Coupled-mode theory^[31]; (b) Guided-mode resonance theory^[33-34] ; (c) Generalized Kerker effect^[35]

Fig. 6. Waveguide array mode expansion^[36-39]

Fig. 7. Electrical circuits type of metagrating diffraction modulation^[45-46]

Fig. 8. Beam-steering using anisotropic or asymmetric metegrating

Fig. 9. Metagrating based on topology optimization

Fig. 10. High efficient beam-steering using rectangle dielectric grating^[55，50]

Fig. 11. (a) Schematic of microfluidic chip with nanostructured and spot-wise functionalized sensor field^[78]; (b) Schematic and (c) optical image of the disposable GMR biosensor chip, consisting of a subwavelength grating (a one-dimensional TiO₂ grating structure) on a cyclic olefin copolymer substrate and a microfluidic module for handing the injection of fluid sample into the sensing area^[80]

Fig. 12. Nanohole array subwavelength grating filters. (a) Transmission spectra of the hole array filters with different side length (a1) 10 μm, (a2) 5 μm, (a3) 2.4 μm, (a4) 1.2 μm^[87]; (b) Color logo based on the nanohole array filter^[88]; (c) oNanohle array filter integrated with CMOS imaging sensor^[89] ; (d) Si subwavelength grating color filters^[90]

Fig. 13. One dimensional nanograting color filters. (a) Schematic diagram and (b) the spectra of the ultrathin Ag nanogratings color filters^[98];(c) Schematic diagram of the nanograting color filters; (d) Relationship between color spectra and period of the color filter nanograting^[100]

Fig. 14. (a) SEM images of silicon nanowire array; (b) Reflection spectra of color filter for different nanowire arrays^[105]; (c) Concept schematic of photoelectric detectors based on vertical silicon nanowires; (d) Color image of test objects taken by silicon nanowire arrays^[106]

Fig. 15. (a) Schematic configuration and (b) reflection spectral responses of the subtractive CMY color filters incorporating a Si-Al hybrid-ND metasurface formed on a Si substrate^[108]; (c) Cross-shaped Si nanoantennas color filters and (d) its transmittance spectra^[113]

Fig. 16. (a) Diagram and (b) absorption spectra of the subwavelength grating (sawtooth anisotropic metamaterial thin film)^[118]; (c) Diagram of MICM (metal-insulator composite multilayer); (d) Comparison of absorption spectra for different structures^[119]

Fig. 17. (a)Absorption spectra of subwavelength grating with nanodisk unit^[123]; (b) Field intensity and energy loss of subwavelength grating with nanodisk unit^[123]; (c) Absorption spectra of subwavelength grating absorber with multilayered metal-dielectric-metal resonant stacks ^[131]. (d) Subwavelength grating of Ti-SiO₂-Al structure for solar energy absorption film^[133]

Fig. 18. (a) Measured absorption spectra of fabricated Ag-SiO₂-Ag cross structure of subwavelength grating with different parameters^[135]; (b) Extinction spectra using crossed trapezoid array subwavelength metagraing^[139]; (c) Absorption spectra of ring array structure^[140]; (d) Absorption spectra of subwavelength grating of cone unit structure^[145]

Fig. 19. (a) Structure and its absorption spectrum of SiO₂-Ge-W^[146]; (b) Experimentally obtained focal ling intensity profiles^[149]; (c)-(d) Structure and its absorption spectrum of SiN_x-TiN- SiO₂^[150]