Large field-of-view polychromatic metalens for full-color scanning fiber endoscopy

Metalenses are a compelling solution to replace refractive lenses in miniaturized imaging systems such as endoscopes. The intrinsic ultrathin thickness and the ease for achieving arbitrarily small diameters facilitate miniaturization of endoscopic systems. This in turn, can potentially open doors for endoscopic applications in tightly confined spaces such as blood vessels and spinal cords. Despite these advantages, traditional metalenses face challenges due to their strong chromatic aberrations, limiting their utility in multi-color imaging. To address this limitation, we present an inverse-designed polychromatic metalens with a diameter of 680 µm and low dispersion across 3 distinct wavelengths 643 nm, 532 nm, and 444 nm,suitable for a tri-color scanning fiber endoscope. The metalens collimates and steers light emitted from a scanning ffber tip to provide illumination of red, green, and blue light, supporting tri-color imaging with a large field-of-view of 70◦. The metalens provides a close-to-diffraction-limited 0.5 ◦ angular resolution, only restricted by the effective aperture of the system. The average relative efficiency of the metalens for on-axis angle among 3 design wavelength is around 32%. This work holds promise for the application of metalenses in endoscopes and other miniaturized imaging systems.