Fig. 11. Dispersion engineering capability of meta-atoms.

a Schematic of a metalens element for visible achromatic imaging. b Phase spectra for five different elements showing the tunability of the group delay by changing the lengths and widths of nanofins. Each colored curve corresponds to its element schematically shown on the right. c The schematic wavefronts of a nonlinear phase compensation scheme. d Effective refractive index spectra of six meta-units listed on the right. e Focal length distribution at different wavelengths. The orange line is the focal length of the nonlinear matched metalens, and the blue line is the normal negative dispersion reference curve. Panels a and b are reproduced with permission⁸⁸. Copyright 2018, The Authors, published by Springer Nature. Panels c–e are reproduced with permission⁹⁸. Copyright 2021, The Authors, preprinted by arXiv