Fig. 5: Optimization results for metalenses.
From: Inverse design and flexible parameterization of meta-optics using algorithmic differentiation
a The unit cell is based on four coupled TiO2 elliptical nanopost resonators, each defined by their respective major and minor axes. The labels Dxi and Dyi denote the x and y semi-diameters of the ith nanopost of the four resonators in the unit cell, respectively. The labels t and p denote the thickness and pitch of the unit cell. An example learning curve where we optimize the electric field magnitude at the desired focal spot, |Efocus|, is shown in (b) and its corresponding normalized intensity profile computed via finite-difference time-domain (FDTD) simulation at the focal plane is presented in (c). Normalized intensity cross sections along the optical axis for several different optimized metalenses with different f-numbers, with the near-field data computed via FDTD, are shown in (d). Focusing efficiency (e), FWHM at best focus (f), and the peak sidelobe ratio (g) are calculated from the FDTD-simulated optimized designs of (d).
