An official website of the United States government
Abstract Nanophotonic devices are optical platforms capable of unprecedented wavefront control. To push the limits of experimental device performance, scalable design methodologies that combine the simplicity and fabricability of conventional design paradigms with the extended capabilities of freeform optimization are required. A novel gradient‐based design framework for large‐area freeform metasurfaces is introduced in which nonlocal interactions between simply shaped nanostructures, placed on an irregular lattice, are tailored to produce high‐order hybridized modes that support customizable large‐angle scattering profiles. Utilizing this approach, multifunctional super‐dispersive metalenses are designed and experimentally demonstrated. The approach to high‐numerical‐aperture radial metalenses capable of diffraction limited focusing and the generation of donut‐shaped point spread functions is also extended. It is anticipated that these concepts will have utility in super‐resolution microscopy, particle trapping, additive manufacturing, and metrology applications that require ultra‐high numerical apertures.
more »
« less
Design, fabrication, and characterization of large metalenses
This work demonstrates the utility of a design, fabrication, and testing loop on 10 mm diameter metalenses to accelerate large-scale production of flat optics. By enabling rapid measurement and analysis of metalenses, it is possible to identify differences between designed performance and as-built performance quickly and correlate those to process characteristics. This accelerated feedback between the design, fabrication, and testing is expected to enable higher yields of better-performing metalenses.
more »
« less
- PAR ID:
- 10517977
- Editor(s):
- Fan, Jonathan A; Chang-Hasnain, Connie J; Zhou, Weimin
- Publisher / Repository:
- SPIE
- Date Published:
- Journal Name:
- SPIE
- ISBN:
- 9781510663664
- Page Range / eLocation ID:
- 25
- Format(s):
- Medium: X
- Location:
- San Francisco, United States
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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
-
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.more » « less
-
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.more » « less
-
Abstract Highly efficient metalens arrays designed for 550 nm are directly printed using UV‐assisted nanoimprint lithography (UV‐NIL) and a TiO2nanoparticle (NP)‐based ink on 8″ optical wafers with imprint times less than 5 min. Approximately one‐thousand 4‐mm metalenses are fabricated per wafer with uniform optical performance using a reusable PDMS‐based elastomeric stamp. The absolute and relative focusing efficiencies are as high as 81.2% and 90.4%, respectively, matching closely with the simulated maximum efficiencies of 83% and 91% achievable with the given master design, indicating that future improvements are possible, and efficiencies are not limited by materials or process. The imprinted metalenses are free from organics due to a post‐imprint calcination step and exhibit outstanding dimensional and optical stabilities. The highest efficiencies are attained using imprint formulations comprised of mixtures of 10 and 20 nm TiO2NPs, whose denser packing not only increases the refractive index (RI) of the calcined lenses up to 2.0 but also reduces the feature shrinkage relative to the master. 25 cycles of atomic layer deposition of TiO2following imprinting increase the RI up to 2.3 without changing dimensions by uniform gap filling between NPs. This work opens a path for true, full‐scale additive manufacturing of metaoptics.more » « less
