Fig. 1. Simulation principle and process of metalens. (a) Working principle of metalens; (b) permittivity distributions of initial value (left) and final result (right) of objective-first inverse design method. Black part represents polymer material constituting device, white part represents air, and gray part lies between the two; (c) 3D metalens structure obtained by rotating 2D planar metalens along its central symmetry axis

Fig. 2. Parameter changes of metalens during iteration process. (a) Residual of metalens, where solid line represents continuous structure and dashed line represents binary structure; (b) binary value of metalens; (c) focusing efficiencies of continuous structure and binary structure; (d) distributions of permittivity of continuous structure and binary structure at 400th iteration

Fig. 3. Simulation of a metalens operating at a wavelength of 1550 nm. (a) E2 normalized intensity distribution for plane containing optical axis; (b) focusing efficiency distributions of metalens from 1300 to 1800 nm, with a focusing efficiency of 72% at 1550 nm; (c) normalized intensity distribution of E2 at focal length; (d) bandwidth of focal full width at half maximum (FWHM) at focal length of metalens from 1400 to 1700 nm

Fig. 4. Metalens structure obtained after offsetting metalens profile by -100, -50, 0, +50, and +100 nm, respectively

Fig. 5. Effect of metalens profile shift on performance. (a) E2 normalized intensity distribution for plane containing optical axis; (b) E2 normalized intensity distribution in x direction at focal plane; (c) bandwidth curves of metalens focusing efficiency at different profile offsets

Fig. 6. 3D FDTD simulation of metalens. (a) E2 normalized intensity distribution at a plane 17.5 μm away from metalens; (b) normalized distribution of electric field intensity for plane containing optical axis; (c) focusing efficiency within a bandwidth from 1300 to 1800 nm; (d) FWHM variation of focal point at focal plane within 1400-1750 nm bandwidth