Fig. 2: Design of the near-IR achromatic metalens.
From: High-efficiency broadband achromatic metalens for near-IR biological imaging window
a The layout of the quarter of the designed metalens. Four fundamental building blocks (unit cells) are enlarged in the insets. b The required group delay for broadband achromatism (solid line) and the values provided by the TiO2 nanostructures. c and d are the numerically calculated focal lengths and efficiencies of TiO2 metalenses with NA = 0.24 (dots) and NA = 0.1 (open squares) at different wavelengths. The diameters of two metalens are 30 and 25 µm, respectively.
