Fig. 6. Metasurfaces for dispersion control at discrete wavelengths. (a) Illustration of the designed multicolor meta-hologram composed of three kinds of aluminum nanorods, each of which controls one wavelength. As a result, images of letter R, G, and B can be generated. (b) Schematic of the dispersive hologram realized by dielectric metasurfaces. The unit cell consists of three different kinds of Si nanoblocks. (c) Schematic of the three-layer metasurfaces lens. Each layer focuses different designed wavelength to the same distance to realize an achromatic metalens. (d) Schematic of a multiwavelength achromatic metasurface to diffract normally incident plane waves at three discrete wavelengths to the same angle θ with respect to z-axis. Each unit cell contains two coupled rectangular Si resonators. (e) Scattering efficiency for one unit cell, which supports three resonances at the target wavelengths. (f) Measured diffraction angles at 1300, 1550 and 1800 nm, which are nearly the same. (g) Schematic of the unit cell (left panel) and the metasurfaces with controllable multiwavelength functions, which can generate different orbital angular momentum at different wavelengths (right panel). (h) The simulated phases at 460, 540 and 700 nm for TiO2 pillars with different width. The black star A indicates the required ideal phase point and red point B means the nearest neighbor of A among those that can be realized in experiments. (a) Reproduced with permission.119 (b) Reproduced with permission.121 (c) Reproduced with permission.116 (d–f) Reproduced with permission.34 (g and h) Reproduced with permission.123.
