Subwavelength-thick lenses with high numerical apertures and large efficiency based on high-contrast transmitarrays

TLDR

Combine: flat optical devices thinner than a wavelength promise to replace conventional components for wavefront and polarization control; transmissive flat lenses are promising for imaging and on-chip integration, but existing designs (plasmonic metasurfaces, high-contrast transmitarrays, gratings) have not matched conventional curved lenses. So: "Flat, sub‑wavelength optical devices promise to replace conventional components for wavefront and polarization control, yet existing transmissive flat‑lens designs have not yet matched the performance of conventional curved lenses for imaging and on‑chip integration." That covers. Purpose sentences: - From [Purpose, Findings] line: "Here we report polarization-insensitive, micron-thick, high-contrast transmitarray micro-lenses with focal spots as small as 0.57 λ." - From [Purpose, Mechanism] line: "A rigorous method for ultrathin lens design, and the trade‑off between high efficiency and small spot size (or large numerical aperture) are discussed." So purpose: They aim to report polarization-insensitive, micron-thick high-contrast transmitarray micro-lenses with sub‑wavelength focal spots, and to present a rigorous design method and discuss trade‑offs between efficiency and spot size/NA. One sentence: "The authors aim to demonstrate polarization‑insensitive, micron‑thick high‑contrast transmitarray micro‑lenses with sub‑wavelength focal spots, and to provide a rigorous design method that discusses the trade‑off between efficiency and spot size or numerical aperture." That seems fine. Mechanism sentences: - From [Purpose, Mechanism] line: same as above but mechanism: "A rigorous method for ultrathin lens design, and the trade‑off between high efficiency and small spot size (or large numerical aperture) are discussed." But that's more purpose.

Abstract

Flat optical devices thinner than a wavelength promise to replace conventional free-space components for wavefront and polarization control. Transmissive flat lenses are particularly interesting for applications in imaging and on-chip optoelectronic integration. Several designs based on plasmonic metasurfaces, high-contrast transmitarrays and gratings have been recently implemented but have not provided a performance comparable to conventional curved lenses. Here we report polarization-insensitive, micron-thick, high-contrast transmitarray micro-lenses with focal spots as small as 0.57 λ. The measured focusing efficiency is up to 82%. A rigorous method for ultrathin lens design, and the trade-off between high efficiency and small spot size (or large numerical aperture) are discussed. The micro-lenses, composed of silicon nano-posts on glass, are fabricated in one lithographic step that could be performed with high-throughput photo or nanoimprint lithography, thus enabling widespread adoption. Replacing conventional components with flat optic devices such as flat lenses is desirable for imaging and on-chip integration, but performance has hindered their use. Here, Arbabi et al. report a wavelength-thin, high-contrast transmitarray micro-lens with a 0.57 λfocal spot and 82% focusing efficiency.