High-quality metalens enables minimally invasive CFB endoscopy

Abstract: Metalenses, owing to their ultra-thin planar structures, present a promising solution for reducing endoscopic invasiveness. However, achieving high-quality imaging with minimal invasiveness (short focal length of metalens) remains a critical challenge. This paper presents a deep learning assisted metalens with a 1mm focal length (corresponding to NA = 0.447) tailored for coherent fiber bundle, constituting the least invasive metalens-CFB system reported to date. To overcome the increased chromatic dispersion and aberrations associated with high NA metalens, we develop a Metalens Image Super-Resolution Generative Adversarial Network to restore images from metalens designed with angularly consistent modulation transfer functions. In parallel, Metal-Height Compensated Etching (MHCE) is applied to compensate for lateral etching at the bottom of high aspect ratio nanopillars, achieving uniform 90{\deg} vertical sidewalls throughout the metalens and improving the phase accuracy. Subsequent experiments with the metalens-CFB system confirm that the metalens expands the field of view of CFB to 48.3{\deg} and extends the depth of field beyond 125 mm. This work accelerates the development of ultra-minimally invasive endoscopic imaging system.