Design of an infrared wide-angle metalens for medical endoscopic imaging systems.

With the development of minimally invasive diagnostic and therapeutic techniques, medical endoscopes face challenges in achieving synergistic optimization of miniaturization, wide field of view (FOV), and high resolution within narrow anatomical environments such as the digestive tract and blood vessels. Traditional refractive lens systems are limited by volume expansion, aberration accumulation, and packaging complexity, making it difficult to meet the precise imaging requirements in complex anatomical scenarios. This paper proposes an innovative design for a single-wavelength near-infrared wide-field metalens based on a doublet metalens architecture. By optimizing the phase distribution of cascaded metasurfaces and the design of nanostructures, the system achieves a ± 50° FOV at a wavelength of 1.5 μm. The system features an aperture of 1.8 mm, relative illuminance > 98.89%, Strehl Ratio > 0.995, and a modulation transfer function (MTF) close to the diffraction limit, exceeding 0.84 at 21 lp/mm. Simulation results show that through the collaborative effect of the corrector plate and focusing metasurface, the doublet metalens maintains a full width at half maximum (FWHM) of 6.212 micrometers and low sidelobe intensity < 1.74% even at the extreme 50° FOV. This study effectively overcomes the field of view-aberration contradiction of single-layer metalenses through the synergistic effect of wavefront pre-compensation and main focusing, significantly enhancing the nanoscale characterization capability of vascular wall microstructures. It provides an innovative solution for miniaturization and high-resolution imaging of medical narrow-bandwidth endoscopes, remarkably strengthening the ability to characterize vascular wall microstructures and demonstrating important clinical application potential.