Metalenses, ultra-thin optical elements that focus light using subwavelength structures, have been the subject of a number of recent investigations. Compared to their refractive counterparts, metalenses offer reduced size and weight, and new functionality such as polarization control. However, metalenses that correct chromatic aberration also suffer from markedly reduced focusing efficiency. Here we introduce a Hybrid Achromatic Metalens (HAML) that overcomes this trade-off and offers improved focusing efficiency over a broad wavelength range from 1000-1800 nm. HAMLs can be designed by combining recursive ray-tracing and simulated phase libraries rather than computationally intensive global search algorithms. Moreover, HAMLs can be fabricated in low-refractive index materials using multi-photon lithography for customization or using molding for mass production. HAMLs demonstrated diffraction limited performance for numerical apertures of 0.27, 0.11, and 0.06, with average focusing efficiencies greater than 60% and maximum efficiencies up to 80%. A more complex design, the air-spaced HAML, introduces a gap between elements to enable even larger diameters and numerical apertures.

We design and fabricate ultra-broadband achromatic metalenses operating from the visible into the short-wave infrared, 450–1700 nm, with diffraction-limited performance. A hybrid 3D architecture, which combines nanoholes with a phase plate, allows realization in low refractive index materials. As a result, two-photon lithography can be used for prototyping while molding can be used for mass production. Experimentally, a 0.27 numerical aperture (NA) metalens exhibits 60% average focusing efficiency and 6% maximum focal length error over the entire bandwidth. In addition, a 200 μm diameter, 0.04 NA metalens was used to demonstrate achromatic imaging over the same broad spectral range. These results show that 3D metalens architectures yield excellent performance even using low-refractive index materials, and that two-photon lithography can produce metalenses operating at visible wavelengths.

Thermal imaging at the infrared wavelength regime has long been applied to different areas such as agriculture and defense industries. Metasurfaces, 2D engineered ultra-thin structures, have attracted much attention due to their compact size, superior performance, and different functionalities at optical frequencies. This work details the design and fabrication of high transmission metalenses operating at the long-wave infrared (LWIR) spectrum. We minimize the reflection losses through anti-reflection coating (ARC) while maintaining the full wavefront control at the central wavelength 9.07 µm. Our unit cell structure provides an average transmission of 97.5%. We experimentally verify our results and show that the fabricated metalenses perform diffraction-limited imaging at the design wavelength.

This work presents the design and fabrication of polymeric, structural optical filters that simultaneously focus light. These filters represent a novel, to the best of our knowledge, design at the boundary between diffractive optics and metasurfaces that may provide significant advantages for both digital and hyperspectral imaging. Filters for visible and near-infrared wavelengths were designed using finite-difference time-domain (FDTD) simulations. Prototype filters were fabricated using two-photon lithography, a form of nanoscale 3D printing, and have geometries suitable to replication by molding. The experimentally measured spectral transmission and focused spot size of each filter show excellent agreement with simulation.

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