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Acquisition of high-resolution images from within internal organs using endoscopic optical imaging has several clinical applications. In particular, endoscopic optical coherence tomography (OCT) capable of visualizing tissue microstructures is emerging as a promising tool for detection, diagnosis, and monitoring of disease in luminal organs. However, difficulties associated with optical aberrations and the trade-off between transverse resolution and depth-of-focus significantly limits the scope of applications. This work presents a new class of optical imaging catheters termed nano-optic endoscopes that address the difficulties associated with current endoscopic imaging catheters. We incorporate a metalens with the ability to modify the phase of incident light at sub-wavelength level into the design of an OCT catheter to achieve near diffraction-limited imaging through negating non-chromatic aberrations. A metalens consists of a 2-dimentional array of subwavelength-spaced scatterers with specific geometric parameters and distribution that locally shift the phase of the incident light and modify its wavefront. The metalens ability to arbitrarily and accurately modify the phase allows the nano-optic endoscope to overcome spherical aberrations and astigmatism, the essential barriers to diffraction-limited imaging. Remarkably, the tailored chromatic dispersion of the metalens in the context of spectral interferometry is utilized to maintain high-resolution imaging beyond the input field Rayleigh range, overcoming the compromise between transverse resolution and depth-of-focus. Endoscopic imaging is demonstrated in resected human and swine airway specimens and in sheep airways in vivo. The versatility and design flexibility of the nano-optic endoscope significantly elevate endoscopic imaging capabilities that will likely impact clinical applications.
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