Fig. 1. Current image sensor technology^[56]. (a) Diagrams of front-side illumination and back-side illumination CMOS image sensors; (b) schematic of Bayer array; (c) development trends of pixel pitch and luminous flux of image sensor

Fig. 2. Typical color filter with micro-nano structure. (a) Structure of planar cavity^[63]; (b) structure of grating waveguide^[31]; (c) structure of metal nanohole array^[76]; (d) dielectric nanostructures^[34]

Fig. 3. Typical color rendering technique based on grating diffraction. (a) Color rendering technique based on blazed gratings and microlens^[81]; (b) color rendering by Dammann gratings^[79]; (c) scanning electron microscope and optical microscopic images of color rendering by Dammann gratings^[83]; (d) color rendering grating with dielectric nanorod structures^[84]

Fig. 4. Typical color rendering technique based on surface plasmon. (a) Beam rendering structure with metal slit^[96]; (b) spatially overlapped subwavelength Bull’s eye structure^[98]; (c) coupled metal nanodisks^[101]; (d) coupling structure of asymmetrical metal nanodisks and metal nanoring^[105]; (e) orthogonal gold and silver nanorods^[106]; (f) single metal nanorod^[108]

Fig. 5. Typical metasurface color rendering techniques. (a) Colorful metasurface hologram imaging^[127]; (b) metalens with four foci for RGGB unit cell based on supercell method^[131]; (c) metalens with three foci for RGB unit cell based on supercell method^[113]; (d) metalens with three foci for RGB unit cell based on staggered phase array method^[129]; (e) focusing of three foci in RGB space based on double layer metalens ^[132]

Fig. 6. Typical dielectric nanoantenna color rendering techniques. (a) Single dielectric nanoantenna^[139]; (b) image sensor with integrated dielectric nanoantennas^[45]; (c) color rendering nanostructures for RGB bands obtained by inverse design^[145]; (d) color rendering nanostructures for multiple wavelengths obtained by inverse design^[147]