Modular snapshot multispectral-panchromatic imager (MSPI) with customized filter arrays.

As one of the simplest methods to construct snapshot spectral imagers, multispectral filter array (MSFA) has been applied to commercial miniatured spectral imagers. While most of them have fixed configurations of spectral channels, lacking flexibility and replaceability. Moreover, conventional MSFA only comprises filtering channels but lacks the panchromatic channel which is essential in detecting dim and indistinct objects. Here, we propose a modular assembly method for snapshot imager which can simultaneously acquire the object's multispectral and panchromatic information based on a customized filter array. The multispectral-panchromatic filter array is batch fabricated and integrated with the imaging senor through a modular mode. Five-band spectral images and a broadband intensity image can be efficiently acquired in a single snapshot photographing. The efficacy and accuracy of the imager are experimentally verified in imaging and spectral measurements. Owing to the modular architecture, our proposed assembly method owns the advantages of compactness, simple assembling, rapid replacement, and customized designing, which overcomes the expensiveness and complexity of scientific-level snapshot spectral imaging systems.

Batch fabrication and compact integration of customized multispectral filter arrays towards snapshot imaging.

Snapshot multispectral imaging (MSI) has been widely employed in the rapid visual inspection by virtues of the non-invasive detection mode and short integration time. As the critical functional elements of snapshot MSI, narrowband, customizable, and pixel-level multispectral filter arrays (MSFAs) that are compatible with imaging sensors are difficult to be efficiently manufactured. Meanwhile, monolithically integrating MSFAs into snapshot multispectral imagers still remains challenging considering the strict alignment precision. Here, we propose a cost-efficient, wafer-level, and customized approach for fabricating transmissive MSFAs based on Fabry-Perot structures, both in the pixel-level and window-tiled configuration, by utilizing the conventional lithography combined with the deposition method. The MSFA chips own a total dimension covering the area of 4.8 mm × 3.6 mm with 4 × 4 bands, possessing the capability to maintain narrow line widths (∼25 nm) across the whole visible frequencies. After the compact integration with the imaging sensor, the MSFAs are validated to be effective in filtering and target identification. Our proposed fabrication method and imaging mode show great potentials to be an alternative to MSFAs production and MSI, by reducing both complexity and cost of manufacturing, while increasing flexibility and customization of imaging system.

New diagonal micropolarizer arrays designed by an improved model in fourier domain.

The design of micropolarizer array (MPA) patterns in Fourier domain provides an efficient approach to reconstruct and investigate the polarization information. Inspired by Alenin's works, in this paper, we propose an improved design model to cover both 2 × N MPAs and other original MPAs, by which an entirely new class of MPA patterns is suggested. The performance of the new patterns is evaluated through Fourier domain analysis and numerical simulations compared with the existing MPAs. Particularly, we analyze the reconstruction accuracy of the first three Stokes parameters and degree of linear polarization (DoLP) in detail. The experimental results confirm that the 2 × 2 × 2 MPA provides the highest reconstruction quality of s0, s1, s2 and DoLP in terms of quantitative measures and visual quality, while the 3 × 3 diagonal MPA achieves the state-of-the-art best results in case of single-snapshot systems. The guidance of this extended model and new diagonal MPAs show its massive potential for the division of focal plane (DoFP) polarization imaging applications.

Wide-Gamut and Polarization-Independent Structural Color at Optical Sub-diffraction-Limit Spatial Resolution Based on Uncoupled LSPPs.

The decreasing pixel size of digital image sensors for high-resolution imaging brings a great challenge for the matching color filters. Currently, the conventional dye color filters with pixel size of several microns set a fundamental limit for the imaging resolution. Here, we put forward a kind of structural color filter with circular nanohole-nanodisk hybrid nanostructure arrays at sub-diffraction-limit spatial resolution based on the uncoupled localized surface plasmon polaritons (LSPPs). Due to the uncoupled LSPPs taking effect, the pixel could generate an individual color even though operating as a single element. The pixel size for the minimum color filtering is as small as 180 × 180 nm2, translating into printing pixels at a resolution of ~ 141,000 dots per inch (dpi). In addition, through both the experimental and numerical investigations, the structural color thus generated exhibits wide color gamut, large viewing angle, and polarization independence. These results indicate that the proposed structural color can have enormous potential for diverse applications in nanoscale optical filters, microscale images for security purposes, and high-density optical data storage.

Polarization-independent and high-efficiency broadband optical absorber in visible light based on nanostructured germanium arrays.

A broadband optical absorber based on the nanostructured germanium (Ge) film composed of single-sized circular nanodisk-nanohole arrays is proposed, which demonstrates high efficiency, strong polarization independence, and large viewing angle. Due to the electric and magnetic resonance absorption modes excited by the nanostructure arrays in highly lossy Ge film, the absorber obtains a high absorptivity, reaching above 90% over the full visible wavelength, and it can be maintained well at a large viewing angle over ±50°. Based on the geometrical symmetry, the absorber is proved to be polarization independent. Moreover, the simple single-sized nanostructure within a certain size tolerance decreases the design and fabrication complexity. The structural configuration with a slight Ge sidewall formed in the nanofabrication process could enhance the overall light absorption. These results indicate that the proposed broadband absorber has great potential in various applications such as anti-reflective coating and perfect cloaking.

Polarization independent subtractive color printing based on ultrathin hexagonal nanodisk-nanohole hybrid structure arrays.

Structural color printing based on plasmonic metasurfaces has been recognized as a promising alternative to the conventional dye colorants, though the color brightness and polarization tolerance are still a great challenge for practical applications. In this work, we report a novel plasmonic metasurface for subtractive color printing employing the ultrathin hexagonal nanodisk-nanohole hybrid structure arrays. Through both the experimental and numerical investigations, the subtractive color thus generated taking advantages of extraordinary low transmission (ELT) exhibits high brightness, polarization independence and wide color tunability by varying key geometrical parameters. In addition, other regular patterns including square, pentagonal and circular shapes are also surveyed, and reveal a high color brightness, wide gamut and polarization independence as well. These results indicate that the demonstrated plasmonic metasurface has various potential applications in high-definition displays, high-density optical data storage, imaging and filtering technologies.

Batch Fabrication of Broadband Metallic Planar Microlenses and Their Arrays Combining Nanosphere Self-Assembly with Conventional Photolithography.

A novel low-cost, batch-fabrication method combining the spin-coating nanosphere lithography (NSL) with the conventional photolithographic technique is demonstrated to efficiently produce the metallic planar microlenses and their arrays. The developed microlenses are composed of subwavelength nanoholes and can focus light effectively in the entire visible spectrum, with the foci sizes close to the Rayleigh diffraction limit. By changing the spacing and diameter of nanoholes, the focusing efficiency can be tuned. Although the random defects commonly exist during the self-assembly of nanospheres, the main focusing performance, e.g., focal length, depth of focus (DOF), and full-width at half-maximum (FWHM), keeps almost invariable. This research provides a cheap way to realize the integrated nanophotonic devices on the wafer level.