Fig. 2. Determination of phase profile for metalens according to Huygens principle.

a A spherical wavefront is given by the envelope of the secondary spherical waves emitted by sub-sources on a surface with a continuous hyperboloidal phase profile. b The meta-atoms impose discrete distribution of phase instead of continuous phase distribution, leading to aberrations related to the wave aberration function (WAF). c The effects of the number of phase discretization levels on the normalized WAF_rms (WAF_rms/λ) and the Strehl ratio (SR), which are represented by red and blue lines, respectively. Inset is the case of 4-level phase discretization. The data are extracted from ref. ¹¹