Silicon Nitride Metalenses for Close-to-One Numerical Aperture and Wide-Angle Visible Imaging

Abstract

Silicon nitride (SiN) is one of the emerging semiconductor materials that are used in both linear and nonlinear all-optical integrated devices. Its excellent dielectric properties, high material stability, and dispersion controllability are attractive to on-chip optical communications, optical signal processing, and even imaging devices. However, a large-aperture SiN metalens with high numerical aperture (NA) is limited by the low refractive index and nanofabrication technologies, particular in the visible spectrum. Here, we experimentally realize the visible-spectrum SiN divergent metalenses by fabricating the 695-nm-thick hexagonal arrays with a minimum space of 42 nm between adjacent nanopillars. A micro-size divergent metalens with NA∼0.98 and subwavelength resolution enables objects to be shrunk as small as a single-mode fiber core. Another centimeter-size SiN divergent metalens with over half a billion nanopillars, made by using the mature CMOS-compatible fabrication process, exhibits high-quality wide-angle imaging. Our findings may open a new door for the miniaturization of optical lenses in the fields of optical fibers, microendoscopes, and smart phones, as well as the applications in all-sky telescopes, large-angle beam shaping, and near-eye imaging.