Fig. 1. Schematic diagram and design principle of the broadband achromatic polarization-insensitive metalenses. (a) Schematic diagram of a broadband achromatic polarization-insensitive metalens (The entire visible light spectrum can be converged into a single focal spot, regardless of polarization). The insets provide a detailed view of the constituent elements of the metalenses. The meta-atom is comprised of two anisotropic nanofins arranged either orthogonally (orthogonal mode) or in parallel (parallel mode) to each other. The structural parameters are p=300 nm，h=900 nm，L₁=140 nm，W₁=60 nm，L₂=50 nm and W₂=290 nm, respectively. The cross-polarized transmittance (T_cross) (b) and the PCE (c) against the wavelength for the nanofins1, nanofins2, parallel mode and orthogonal mode, respectively

Fig. 2. Broadband achromatic focusing performance of our proposed metalens. Simulated normalized intensity distributions in the x-z planes for the designed broadband achromatic metalens (a), sub-metalens 1(b), and sub-metalens 2(c) under LCP light incidence across the visible light of 470 to 650 nm with a step of 30 nm. The white dashed lines correspond to the predetermined focal length of 40 μm, and the insets (depicted by red solid lines) in (a) illustrate normalized intensity profiles along the z=40 μm cut plane

Fig. 3. Quantization of focal length of the designed broadband achromatic metalens. (a)-(c) The normalized intensity distributions along the x=0 cross-section of the designed broadband achromatic metalens, sub-metalens1, and sub-metalens2 under LCP incidence with different wavelengths. (d) Simulated focal lengths and focal length shifts functioning versus wavelength for the broadband achromatic metalens, sub-metalens1, and sub-metalens2

Fig. 4. Quantification of focusing efficiency and intensity of the designed broadband achromatic metalens. (a) The simulated peak intensities and full widths at half maximum (FWHMs) of focal spots versus the sampled wavelengths for the designed broadband achromatic metalens. The pink dashed line represents the corresponding theoretical diffraction limits; (b) The simulated focusing efficiencies and depth of focus of focal spots versus the sampled wavelengths for the designed broadband achromatic metalens

Fig. 5. Polarization insensitive focusing performance of the designed metalens. (a) Simulated intensity profiles in the x-z planes for the designed broadband achromatic metalens under linearly, circularly, and elliptically polarized lights; (b) Simulated focal lengths and focal length shifts versus the incident polarization states; (c) The simulated peak intensities and full widths at half maximum (FWHMs) of focal spots versusthe incident polarization states for the designed broadband achromatic metalens (the pink dashed line represents the corresponding theoretical diffraction limits); (d) Simulated focusing efficiencies and depth of focus of focal spots versus the sampled wavelengths for the designed broadband achromatic metalens