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

Abstract

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 ∼140 μm at the center of field (imaging distance 15 mm), an FOV of ∼70 deg, and a depth-of-focus of ∼15 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 ∼3 times resolution degradation.Conclusions: These results show the promise of integrating a metalens into an endoscope for device minimization and optical performance improvement.

Wide field-of-view metalens: a tutorial

“…[139][140][141][142] Meta-optic fiber endoscopes and scanning fiber endoscopes have been explored with WFOV and colored imaging recently. 143,144 Endoscopy is only one example highlighting the potential applications of WFOV metalenses in the biomedical imaging arena. Other promising use scenarios include portable or miniature microscopy, 145 wide-field retinal imaging, and 3-D microscopy.…”

“…Emerging techniques facilitating integration of metasurfaces on fiber facets also envisage novel miniaturized endoscopic probes with enhanced and versatile imaging capabilities 139 – 142 Meta-optic fiber endoscopes and scanning fiber endoscopes have been explored with WFOV and colored imaging recently 143 , 144 …”

Spectrally Encoded Nonscanning Imaging through a Fiber

“…The capability to see through a single optical fiber or a small bundle with extremely small device dimensions holds the potential to drastically transform the field of biomedical endoscopy, as sutureless surgery would become possible. Various approaches to this problem have been explored, including fiber-optic confocal microscopy, , scanning fiber endoscopy, , coherent fiber bundles, and micro-electromechanical systems-scanned optical coherence tomography endoscopic probes. , In scanning-based modalities, an image is formed by scanning the fiber , or the beam at the distal end, , which results in bulky devices, relatively complicated integration, and low speed. , On the other hand, an ordered fiber array (i.e., a coherent fiber bundle) , enables direct imaging combined with a lens, but the resolution is ultimately limited by the number of fibers ∼10,000 in the bundle and typically has a larger diameter (∼1 mm).…”

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

“…Leveraging their ultra-thin thickness and the ease of aperture reduction, metalenses have been integrated into various kinds of endoscopic systems, including coherent fiber bundle endoscopes, 8,9 fluorescence confocal endoscopes, 10,11 optical coherence tomographic endoscopes, 12 and scanning fiber endoscopes. 13 However, a metalens exhibits a pronounced dispersion in wavelength, akin to other diffractive lenses, where the focal length is inversely proportional to the wavelength. 14 This significant dispersion introduces severe chromatic aberrations, impeding the adoption of metalenses in multicolor imaging applications.…”