A Hybrid Achromatic Metalens

TL;DR

This paper introduces a Hybrid Achromatic Metalens (HAML) that achieves broad wavelength focusing with high efficiency, overcoming previous trade-offs between chromatic correction and focusing efficiency in ultra-thin optical elements.

Contribution

The paper presents a novel HAML design method combining ray-tracing and phase libraries, enabling efficient fabrication and broad-spectrum achromatic focusing.

Findings

Achieved diffraction-limited performance with NA up to 0.27

Focusing efficiencies exceeded 60% on average

Operates effectively over 1000-1800 nm wavelength range

Abstract

Metamaterials and metasurfaces are widely used to manipulate electromagnetic waves over a broad range of wavelengths. Several recent efforts have focused on metalenses, ultra-thin optical elements that focus light using subwavelength structures. Compared to their refractive counterparts, metalenses offer reduced size and weight, improved manufacturability, and new functionality such as polarization control. However, metalenses that correct chromatic aberration also suffer from markedly reduced focusing efficiency. Here we introduce a Hybrid Achromatic Metalens (HAML), that overcomes this trade-off and offers improved focusing efficiency over a broad wavelength range from 1000 - 1800 nm. Fabricated HAMLs demonstrated diffraction limited performance for numerical apertures (NA) of 0.27, 0.11, and 0.06 with average focusing efficiencies $> 60\%$ and maximum efficiencies ~ $ 80\%$. HAMLs can be designed by combining recursive ray-tracing and simulated phase libraries rather than computational intensive global search algorithms. Moreover, HAMLs can be fabricated in low-refractive index materials using multi-photon lithography for customization or using molding for mass production.