Fig. 1. Schematic of focusing by metalens

Fig. 2. Flow chart of particle swarm optimization algorithm

Fig. 3. Phase of unit column under different widths and wavelengths

Fig. 4. Comparison between standard focus phase profile and optimized phase profile at different wavelengths.(a) 500 nm; (b) 510 nm; (c) 520 nm; (d) 530 nm; (e) 540 nm; (f) 550 nm

Fig. 5. Unit nanopillar and structural arrangement of metalens. (a)Top view of metalens structure; (b) unit nanopillar; (c) top view of unit nanopillar

Fig. 6. Focus comparison between achromatic metalens and chromatic metalens. (a) Achromatic; (b)chromatic

Fig. 7. Reflectivity of reflected beam in xoy plane under different wavelengths

Fig. 8. Diffraction efficiency of polarized incident light