Fig. 1: Design of achromatic flat lens with high NA.
a Schematic of an achromatic flat lens. b Phase profiles of the conventional achromatic metalens. The focus length f and the maximum phase dispersion of the meta-atoms are set to be 9.7 μm and 2.20π, respectively. The achromatic operating is set within the wavelength range of 650 nm to 1000 nm. The gray region indicates the inherent size limitation of this achromatic flat lens if it is solely composed of conventional metalens. The corresponding maximum radius and NA of the conventional achromatic metalens are r0 = 6.6 μm and NA = 0.56, respectively. Inset is the schematic of the metalens. c The phase profiles of the meta-atoms φmeta (r, ω) (solid lines), the relative phase ΔωΔL(r)/c corresponding to the SPDC layer (dashed lines) and (d) the relative phase φlens (r,ω) – φlens (R,ω) of the achromatic flat lens shown in (a). The parameters are identical to those in Fig. 1b. The corresponding maximum radius and NA of the flat lens are r6 = 20.1 μm and NA = 0.9, respectively. If using a conventional achromatic metalens to achieve the phase control of (d), then the required maximum phase dispersion of the meta-atoms would need to reach ΔΦmeta = 13.60π. Inset is the schematic of the achromatic flat lens
