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

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.