Nanostructure-Empowered Efficient Coupling of Light into Optical Fibers at Extraordinarily Large Angles

Abstract

Coupling of light from free space to optical fibers is essential for many applications, while commonly used step-index optical fibers provide insufficient coupling efficiencies especially at large angles of incidence. Here, we demonstrate record-high coupling efficiencies achieved with dielectric nanostructures located on single-mode fiber end faces. We introduce a novel approach that allows fabricating dielectric nanostructures at the facet of a step-index optical fiber via an extended version of planar electron-beam based lithography. We demonstrate polarization- and angle-independent coupling of light into the fiber across a wide range of angles as large as 80°. We support our experimental results with an analytical model and extensive numerical simulations. Our results reveal the key properties of nanostructure-empowered fibers that may improve the performance of many optical devices requiring efficient collection of light, including quantum technologies (single-photon collection) or biophotonics (in vivo imaging). Our approach can be extended to other materials and geometries, merging fiber optics with high-index dielectric metasurfaces, allowing for unprecedented functionalities for the efficient control of light.