Inverse Design of Large-scale Metalens for Advanced Optical Applications

Abstract

Metalenses offer a significantly smaller size compared to conventional lenses while achieving high optical performance. However, it is difficult to design hundreds of micrometers or more of metallens. Therefore, it is difficult to develop an metalens for application. To overcome these limitations, this paper utilizes MEEP's adjoint solver and cylindrical symmetry to efficiently design large-aperture metalenses. Initially, we designed a single-layer achromatic metalens with a diameter of 544.7 μm, a numerical aperture (NA) of 0.29, and a focal length of 900 μm, operating at wavelengths R (635 nm), G (532 nm), and B (635 nm). This allowed us to confirm the feasibility of achromatic metalens design using MEEP. The designed metalens demonstrates a longitudinal chromatic aberration of less than 1 μm and achieves a focusing efficiency of 6.5% across the three wavelengths. To achieve higher optical performance, we designed a multi-layer metalens with a 3-layer structure. A longitudinal chromatic aberration of the multi-layer metalens remains below 1 μm, and the focusing efficiency significantly surpasses that of the single-layer metalens, reaching 15.6% for R, 14.9% for G, and 13.0% for B wavelengths, more than doubling the performance of the single-layer metalens. Additionally, the modulation transfer function (MTF) values at 100lp/mm are all above 0.8 for the three wavelengths. While this research focused on designing R, G, B achromatic metalenses with a diameter of 544.7 μm, increasing the number of figures of merit (FOMs) would enable the design of achromatic metalenses operating in a broader spectral range. Furthermore, it is anticipated that updating the optimization code segments would allow for the design of achromatic metalenses with a large field of view.