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1. Height-modulation of diffraction gratings by light-controlled capillary force lithography for structural coloring

   https://doi.org/10.1117/12.2650950  

   Ji, Myung Gi; Kim, Jaeyoun (March 2023, PROCEEDINGS SPIE OPTO, MOEMS and Miniaturized Systems XXII)

   Piyawattanametha, Wibool; Park, Yong-Hwa; Zappe, Hans (Ed.)

   Diffraction gratings are ubiquitous in many optical applications such as sensors, filters, and optical security devices. Capillary force lithography, which utilizes the capillary rise of photopolymer into nanoscale cavities, is a simple and rapid method to construct diffraction gratings without necessitating expensive instruments or complex steps. With the help of spatial light modulators, such as the digital micromirror device, the height of the grating can also be spatially modulated, printing spatially height-modulated gratings. When white light normally impinges on the grating, the light propagates into the grating interferes with light that propagates into air. By varying the height of the grating, the optical path lengths of two lights can be varied, leading to different interference effects and structural coloring. Judicious design of the grating’s parameters and patterning process will even allow encoding of multiple images. In this work, by tuning the height of the grating through the light-controlled capillary force lithography, we demonstrate grating-based structural color printing. This technique is promising for producing the custom patterns for anti-counterfeiting, authentication, and cryptography. 

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2. Diffractive microoptics in porous silicon oxide by grayscale lithography

   https://doi.org/10.1364/OE.538142  

   Siegle, Leander; Xie, Dajie; Richards, Corey_A; Braun, Paul_V; Giessen, Harald (September 2024, Optics Express)

   We demonstrate focusing as well as imaging using diffractive microoptics, manufactured by two-photon polymerization grayscale lithography (2GL), that have been 3D printed into porous silicon oxide. While typical doublet lens systems require support structures that hold the lenses in place, our optics are held by the porous media itself, decreasing both the fabrication time and design constraints while increasing the optically active area. Compared to the typical two-photon polymerization fabrication process, 2GL offers better shape accuracy while simultaneously increasing throughput. To showcase 2GL manufactured optics in porous media, we fabricate singlet diffractive lenses with a diameter of 500 µm and numerical apertures of up to 0.6. We measure the intensity distribution in the focal plane, and along the optical axis. Furthermore, we design and fabricate a doublet lens system for imaging purposes with a diameter of 600 µm and thinner than 60 µm. We examine the imaging performance with a USAF 1951 resolution test chart and determine the resolution to be 287 lp/mm. 3D printing in porous SiO₂thus holds great promise for future complex and unconventional microoptical solutions. 

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3. Optimal binary gratings for multi-wavelength magneto-optical traps

   https://doi.org/10.1364/OE.498606  

   Burrow, Oliver S.; Fasano, Robert J.; Brand, Wesley; Wright, Michael W.; Li, Wenbo; Ludlow, Andrew D.; Riis, Erling; Griffin, Paul F.; Arnold, Aidan S. (January 2023, Optics Express)

   Grating magneto-optical traps are an enabling quantum technology for portable metrological devices with ultracold atoms. However, beam diffraction efficiency and angle are affected by wavelength, creating a single-optic design challenge for laser cooling in two stages at two distinct wavelengths – as commonly used for loading, e.g., Sr or Yb atoms into optical lattice or tweezer clocks. Here, we optically characterize a wide variety of binary gratings at different wavelengths to find a simple empirical fit to experimental grating diffraction efficiency data in terms of dimensionless etch depth and period for various duty cycles. The model avoids complex 3D light-grating surface calculations, yet still yields results accurate to a few percent across a broad range of parameters. Gratings optimized for two (or more) wavelengths can now be designed in an informed manner suitable for a wide class of atomic species enabling advanced quantum technologies. 

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4. High-efficiency 2D grating design for the magneto-optical trap: enhancing intensity balance and reducing optical complexity

   https://doi.org/10.1117/1.OE.64.8.085106  

   Karooby, Elaheh; Li, Jiazhen; Agrawal, Amit; Gu, Qing (August 2025, Optical Engineering)

   Integrated diffraction gratings offer a compact route to magneto-optical traps (MOTs) for atom cooling and trapping, thus preparing MOTs for future scalable quantum systems. While segmented tri-gratings ensure axial radiation pressure balance, they are limited in optical trapping volume. Planar 2D gratings, though offer larger trapping regions, suffer from low diffraction efficiency and the resulting axial pressure imbalance, necessitating the use of a neutral density (ND) filter to achieve this balance. We present a numerically optimized 2D diffraction grating design that overcomes these limitations and satisfies the required optical conditions for laser cooling, namely, radiation pressure balance, specular reflection cancellation, and circular polarization handedness reversal upon diffraction, thus achieving an optical molasses – a necessary condition in MOT. Using Rigorous Coupled Wave Analysis (RCWA) and a Genetic Algorithm (GA), we design a grating for (_ ^87)Rb grating MOT (GMOT) that achieves a 24% first-order diffraction efficiency, of which 99.7% have the correct circular handedness. These properties enable efficient atom cooling without an ND filter when used with a flat-top beam inside the vacuum chamber. Our design simplifies optical alignment, reduces system footprint, and advances the integration of GMOTs into compact quantum devices. 

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5. Toward implantable devices for angle-sensitive, lens-less, multifluorescent, single-photon lifetime imaging in the brain using Fabry–Perot and absorptive color filters

   https://doi.org/10.1038/s41377-022-00708-9  

   Taal, Adriaan J.; Lee, Changhyuk; Choi, Jaebin; Hellenkamp, Björn; Shepard, Kenneth L. (December 2022, Light: Science & Applications)

   Abstract Implantable image sensors have the potential to revolutionize neuroscience. Due to their small form factor requirements; however, conventional filters and optics cannot be implemented. These limitations obstruct high-resolution imaging of large neural densities. Recent advances in angle-sensitive image sensors and single-photon avalanche diodes have provided a path toward ultrathin lens-less fluorescence imaging, enabling plenoptic sensing by extending sensing capabilities to include photon arrival time and incident angle, thereby providing the opportunity for separability of fluorescence point sources within the context of light-field microscopy (LFM). However, the addition of spectral sensitivity to angle-sensitive LFM reduces imager resolution because each wavelength requires a separate pixel subset. Here, we present a 1024-pixel, 50  µm thick implantable shank-based neural imager with color-filter-grating-based angle-sensitive pixels. This angular-spectral sensitive front end combines a metal–insulator–metal (MIM) Fabry–Perot color filter and diffractive optics to produce the measurement of orthogonal light-field information from two distinct colors within a single photodetector. The result is the ability to add independent color sensing to LFM while doubling the effective pixel density. The implantable imager combines angular-spectral and temporal information to demix and localize multispectral fluorescent targets. In this initial prototype, this is demonstrated with 45 μm diameter fluorescently labeled beads in scattering medium. Fluorescent lifetime imaging is exploited to further aid source separation, in addition to detecting pH through lifetime changes in fluorescent dyes. While these initial fluorescent targets are considerably brighter than fluorescently labeled neurons, further improvements will allow the application of these techniques to in-vivo multifluorescent structural and functional neural imaging. 

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