High efficiency near diffraction-limited mid-infrared flat lenses based on metasurface reflectarrays

TL;DR

This paper presents a metasurface flat lens for mid-infrared light that achieves near diffraction-limited focusing with high efficiency, using simple fabrication methods and a design that simplifies experimental setup.

Contribution

The authors demonstrate a high-efficiency, near diffraction-limited flat lens based on metasurface reflectarrays for mid-infrared wavelengths, with simplified geometry and scalable fabrication.

Findings

Achieved 80% experimental focusing efficiency at 4.6 μm

Designed for near diffraction-limited focusing at 45° incidence

Utilized single-step photolithography for large-scale production

Abstract

A limiting factor in the development of mid-infrared optics is the lack of abundant materials that are transparent, low cost, lightweight, and easy to machine. In this paper, we demonstrate a metasurface device that circumvents these limitations. A flat lens based on antenna reflectarrays was designed to achieve near diffraction-limited focusing with a high efficiency (experiment: 80%, simulation: 83%) at 45(o) incidence angle at {\lambda} = 4.6 {\mu}m. This geometry considerably simplifies the experimental arrangement compared to the common geometry of normal incidence which requires beam splitters. Simulations show that the effect of comatic aberrations is small compared to parabolic mirrors. The use of single-step photolithography allows large scale fabrication.