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Metasurfaces have been studied and widely applied to optical systems. A metasurface-based flat lens (metalens) holds promise in wave-front engineering for multiple applications. The metalens has become a breakthrough technology for miniaturized optical system development, due to its outstanding characteristics, such as ultrathinness and cost-effectiveness. Compared to conventional macro- or meso-scale optics manufacturing methods, the micro-machining process for metalenses is relatively straightforward and more suitable for mass production. Due to their remarkable abilities and superior optical performance, metalenses in refractive or diffractive mode could potentially replace traditional optics. In this review, we give a brief overview of the most recent studies on metalenses and their applications with a specific focus on miniaturized optical imaging and sensing systems. We discuss approaches for overcoming technical challenges in the bio-optics field, including a large field of view (FOV), chromatic aberration, and high-resolution imaging.
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Inverse-designed large field-of-view polychromatic metalens for tri-color scanning fiber endoscopy
Abstract Metalenses, with their ultrathin thicknesses and their ease for achieving ultra small diameters, offer a promising alternative to refractive lenses in miniaturized imaging systems, such as endoscopes, potentially enabling applications in tightly confined spaces. However, traditional metalenses suffer from strong chromatic aberrations, limiting their utility in multi-color imaging. To address this limitation, here we present an inverse-designed polychromatic metalens with a diameter of 680 μm, focal length of 400 μm, and low dispersion across 3 distinct wavelengths at 643 nm, 532 nm, and 444 nm. The metalens collimates and steers light emitted from a scanning fiber tip, generating scanning beams across a 70° field-of-view to provide illumination for a scan-based imaging. 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 among three design wavelengths is around 32% for on-axis angle and 13% averaged across the entire field-of-view. This work holds promise for the application of metalenses in endoscopes and other miniaturized imaging systems.
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- Award ID(s):
- 2025489
- PAR ID:
- 10595745
- Publisher / Repository:
- NatureSpringer
- Date Published:
- Journal Name:
- Communications Engineering
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2731-3395
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Theoretical bounds are commonly used to assess the limitations of photonic design. Here we introduce a more active way to use theoretical bounds, integrating them into part of the design process and identifying optimal system parameters that maximize the efficiency limit itself. As an example, we consider wide-field-of-view high-numerical-aperture metalenses, which can be used for high-resolution imaging in microscopy and endoscopy, but no existing design has achieved a high efficiency. By choosing aperture sizes to maximize an efficiency bound, setting the thickness according to a thickness bound, and then performing inverse design, we come up with high-numerical-aperture (NA=0.9) metalens designs with, to our knowledge, record-high 98% transmission efficiency and 92% Strehl ratio across all incident angles within a 60° field of view, reaching the maximized bound. This maximizing-efficiency-limit approach applies to any multi-channel system and can help a wide range of optical devices reach their highest possible performance.more » « less
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Abstract Femtosecond laser‐induced damage threshold (LIDT) testing is carried out at 515 nm on 4‐mm‐sized metalens arrays that are manufactured by direct nanoimprinting of a TiO2nanoparticle (NP)‐based ink containing either polymeric or inorganic binders. The all‐inorganic TiO2metalenses exhibit ≈80% absolute focusing efficiency and demonstrate an LIDT of ≈90 mJ cm−2based on a single‐shot determination using Liu's method, while the metalenses with the polymeric binder achieve ≈137 mJ cm−2and an efficiency of ≈76%. Despite the higher LIDT of the TiO2‐polymer composite metalenses in the single‐shot experiment, these lenses exhibit significant damage at fluences as low as ≈8 mJ cm−2when subjected to ≈6 × 10⁸ pulses at 60 kHz. On the other hand, the all‐inorganic metalenses remain intact under identical conditions at ≈64 mJ cm−2. That is, the inorganic binder provides superior long‐term stability relative to the polymeric binder and is a more viable solution for high‐energy applications. Structural damages observed in nanostructures result in a reduced deflection efficiency and increase light scattering at the focal plane of the metalens. The LIDT testing is also performed in the nanosecond regime at 532 and 1064 nm with the all‐inorganic metalenses, yielding thresholds of ≈0.5 and ≈5 J cm−2, respectively.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1038/s44172-025-00377-7
