Fig. 2: Comparison of metalens design methodologies: conventional intuitive design by library search vs. inverse design by evolutionary optimization.
From: Inverse design of metasurfaces with non-local interactions
a Ideal phase profile of a focusing lens. The inset equation corresponds to the 1D phase profile of a cylindrical lens, where x is the radial position relative to the lens center and f is the focal length. b A pre-determined meta-atom library (disc radius vs. phase shift diagram), similar to Fig. 1c. The phase profile is discretized using sub-wavelength meta-atoms with radius obtained from the pre-determined library, in order to generate a phase profile that is closest to the continuous phase profile. c A typical metalens layout designed by library search. The appropriate discs are placed in a constant-pitch lattice, in order to reproduce the ideal phase map. d Electric energy density distribution in the x–z cross-section of an ideal focusing lens. The lens is illuminated by an incident plane wave from the bottom and focuses the light to a focal spot at a distance f above the lens plane. e Evolutionary optimization workflow: genetic algorithm with an interface to FDTD simulation. f A typical aperiodic metalens layout designed by evolutionary optimization.
