High-quality metalens enables minimally invasive CFB endoscopy

TL;DR

This paper introduces a deep learning assisted, high-quality metalens with a 1mm focal length for coherent fiber bundle endoscopy, significantly reducing invasiveness while maintaining imaging performance.

Contribution

It presents a novel fabrication method for high aspect ratio nanopillars to correct aberrations in ultra-miniature metalenses for minimally invasive endoscopy.

Findings

Achieved a 48.3° field of view with the metalens-CFB system.

Demonstrated a depth of field exceeding 125 mm.

Fabricated a metalens with nearly vertical nanopillar sidewalls for improved phase accuracy.

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 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 compensate for lateral etching at the base of the nanopillars by adjusting the thickness of a sacrificial hard mask. This approach enables the fabrication of nanopillars with small cross sections and high aspect ratios, featuring nearly vertical sidewalls (~90{\deg}), thereby enhancing the phase accuracy of the metalens. Experimental validation using the metalens-CFB system demonstrates that the metalens achieves an expanded field of view of 48.3{\deg} and a depth of field exceeding 125 mm. This work establishes a new paradigm for ultra-minimally invasive endoscopic imaging.