Fig. 1. (a) Working principle of a continuous-zoom metalens. (b) Diagram of a nanobrick unit structure. Each nanobrick was designed with length L=140nm, width W=70nm, height H=350nm, and cell size C=300nm at an operation wavelength of 633 nm. ϕ is the orientation angle of the nanobrick, and the incident light propagates along the z-axis direction. (c) Schematic diagram of one of the designed GEMSs. (d) The co-polarization and cross-polarization transmissivities of a nanobrick. The simulation was run by normally illuminating a nanobrick with a beam of CP light and under the boundary condition of a period.

Fig. 2. Focal length of the metalens as a function of the mutual rotation angle between two GEMSs. With LCP incident light, the metalens acts as a positive zoom lens and its focal length changes from +∞ to nearly zero like the blue curve. When the incident light is switched to RCP, the metalens becomes a negative one, and its focal length ranges from −∞ to nearly zero. In this example, the metalens dimension is 30.3μm×30.3μm, the constant a is 0.1μm−2, and the operation wavelength is 633 nm.

Fig. 3. Simulation of a zoom metalens. Full-wave numerical simulations were performed by FDTD Solutions for the propagation of LCP incident light. (a)–(c) Intensity of the electric field along the direction of light propagation (z axis) corresponding to θ=30°, 45°, and 75°, respectively. The back surface of the metalens is placed at z=0μm.

Fig. 4. Simulation results at the focal plane of the metalens. (a)–(c) Intensity of the electric field at the cross-section of the focal plane corresponding to θ=30°, 45°, and 75°, respectively. The Airy disks marked by white curves are calculated with the diffraction limit principle, and their radii are 2.42 μm (θ=30°), 1.61 μm (θ=45°), and 0.97 μm (θ=75°), respectively.

Fig. 5. Simulation of a zoom metalens. (a), (b) The simulation domains show the distribution of phase along the direction of light propagation (z axis) for θ=75°(f=−37.9μm) and θ=30°(f=−94.8μm), respectively. (c), (d) Compared with the negative focal length case, the simulation domains show the phase distribution of θ=75°(f=37.9μm) and θ=30°(f=94.8μm) with LCP light incidence.

Fig. 6. A variation tendency of the focal length for the corrected metalens. (a)–(d) Intensity of the electric field along the direction of light propagation (z axis) corresponding to θ=−90°(f=+∞), θ=−45°(f=63.1μm), θ=0°(f=31.5μm), and θ=45°(f=21.0μm), respectively. The corrected metalens is illuminated by a beam of LCP incident light.