Large field-of-view short-wave infrared metalens for scanning fiber endoscopy

Significance: The scanning fiber endoscope (SFE), an ultrasmall optical imaging device with a large field-of-view (FOV) for having a clear forward view into the interior of blood vessels, has great potential in the cardiovascular disease diagnosis and surgery assistance, which is one of the key applications for short-wave infrared biomedical imaging. The state-of-the-art SFE system uses a miniaturized refractive spherical lens doublet for beam projection. A metalens is a promising alternative that can be made much thinner and has fewer off-axis aberrations than its refractive counterpart.

Aim: We demonstrate a transmissive metalens working at 1310 nm for a forward viewing endoscope to achieve a shorter device length and better resolution at large field angles.

Approach: We optimize the metalens of the SFE system using Zemax, fabricate it using e-beam lithography, characterize its optical performances, and compare them with the simulations.

Results: The SFE system has a resolution of $\sim 140\mu m$ at the center of field (imaging distance 15 mm), an FOV of $\sim 70\mathrm{deg}$ , and a depth-of-focus of $\sim 15\mathrm{mm}$ , which are comparable with a state-of-the-art refractive lens SFE. The use of the metalens reduces the length of the optical track from 1.2 to 0.86 mm. The resolution of our metalens-based SFE drops by less than a factor of 2 at the edge of the FOV, whereas the refractive lens counterpart has a $\sim 3$ times resolution degradation.

Conclusions: These results show the promise of integrating a metalens into an endoscope for device minimization and optical performance improvement.