Fig. 1. Structure of metasurfaces. (a) P-B metasurface; (b) Transmission metasurface; (c)-(d) The phase shift and transmission amplitude vary with cylinder diameter, when the metasurfaces use SiO₂ as substrate, TiO₂ as nanoantennas in (c) and Si₃N₄ as nanoantennas in (d). The p is 0.42 μm and the H is 1.0 μm

Fig. 2. Transmission amplitude and phase shift of the transmitted light through Si₃N₄ metasurfaces with different D, p and H (Metasurfaces use cylindrical nanoantennas)

Fig. 3. Metasurface using Si₃N₄ nanoantennas. (a) Maximum duty cycle of cylindrical nanoantennas; (b) Maximum duty cycle of square post nanoantennas; (c)-(d) Correspondence between phase shift and side length of square posts when p is 0.47 μm and 0.48 μm

Fig. 4. Metasurfaces simulation with different focal length. (a) Square post antenna arrangement of metasurfaces; (b) Schematic diagram of metasurfaces focusing; (c) Electric field distribution in xz plane of metasurfaces with different focal lengths; (d) Electric field distribution in xy plane of metasurfaces with different focal lengths

Fig. 5. Simulation results of metasurfaces with different focal lengths. (a) Focusing spot size changes with f/D_m; (b) Transmittance and focusing efficiency of metasurfaces with different focal lengths; (c) The deviation between actual focal length and theoretical focal length; (d) When the theoretical focal length is 200 μm, the focal length of the metasurfaces changes with the aperture

Fig. 6. Analysis of dispersion characteristics of metasurfaces. (a) MTF at different bandwidths of metasurfaces with a focal length of 100 μm; (b) The focal length of the metasurfaces varies with the central wavelength of the incident light

Table 1. Nanoantennas' side length L and its corresponding phase shift φ

Table 2. Simulation results of metasurfaces with different focal lengths