Fig. 1. Design scheme of the metalens for coaxial double wavelength focusing. (a) The phase modulation for the laser with a wavelength of λ1; (b) the phase modulation of a vortex with a topological charge of one; (c) the phase modulation combining (a) and (b) for the laser with a wavelength of λ2; (d) the meta-molecular structure unit.

Fig. 2. Schematic diagram of the designed metalens for coaxial double wavelength focusing.

Fig. 3. FDTD-simulated focusing spot for designed metalens. (a) The circular solid spot for the first laser with λ1; (b) the doughnut-shaped focusing spot for second laser with λ2.

Fig. 4. Local magnified SEM image of the fabricated metalens.

Fig. 5. Experimental setup for verifying the functionality of the designed metalens.

Fig. 6. Experimental result that is captured by a CCD camera.