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Snapshot spectral imaging with parallel metasystems

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Science Advances  18 Sep 2020:
Vol. 6, no. 38, eabc7646
DOI: 10.1126/sciadv.abc7646
  • Fig. 1 Schematic of proposed MSSI and principle of operation.

    (A) Side view and (B) top view. A 4 × 5 array of doublet lenses comprising two metasurfaces is aligned to a matched array of metasurface bandpass filters resting on an image sensor. (C) The doublet lens array images an object composed of mixed spectral content. Filters discriminate light traversing the doublet lenses into spectral channels. (D) Individual channels are registered to form a 3D spectral datacube.

  • Fig. 2 Metasurface bandpass filter array.

    (A) Schematics. Each bandpass filter consists of two DBRs that form a Fabry-Pérot cavity. A layer of SU-8 polymer separates the DBRs, and a uniform array of α-Si nanoposts rests on the lower DBR. Nanopost diameter determines each filter’s passband. (B) Simulated transmission passbands for filters with nanopost diameters ranging from 0 to 230 nm. (C) Optical micrograph of the completed filter array and electron micrograph of the nanopost array in the filter’s interior (inset). (D) Measured transmission passbands for a subset of the filter array.

  • Fig. 3 Metasurface doublet array.

    (A) Ray diagrams showing fields incident at 0° and 10°. (B) Example spot diagram for fields incident at 0° and 10° for one of the doublets with a design wavelength of λ0 = 872.8 nm. Green dots indicate λ0, and red and blue dots nearby wavelengths inside the filter passband (λ0 ± 4.7 nm). The black circle marks the first zero of the Airy pattern. (C) Schematic of doublet array. Both corrector and focuser metasurfaces are implemented by nonuniform, rectangular arrays (320-nm lattice constant) of square, 485-nm-tall α-Si nanoposts encapsulated in SU-8 polymer. (D) Optical micrograph showing a portion of the focuser array. (E) Measurement setup and (F) measured focal spots for light at 0°, 5°, and 10° incidence. Focal spots share an intensity scale. Line graph shows cross section at 0 (black, solid) with Airy pattern (red, dashed) for comparison. (G) Illustration depicting the problem of reflective field stops. An errant ray (blue) rejected by one filter (green) bounces off a reflective field stop (gold) into a neighboring channel, contributing noise. (H) Schematic of absorptive apertures showing Al2O3-protected SU-8 polymer without Ti deposition (R1), Al2O3-protected SU-8 polymer with Ti deposition (R2), etched SU-8 polymer with Ti deposition (R3), and etched SU-8 polymer without Ti deposition (R4). (I) Photo of test sample showing regions labeled in (H) and electron micrograph of etched SU-8 polymer. R1 is transparent, showing the cloth behind the substrate; R2 is opaque and reflective; R3 is opaque and absorptive; and R4 is diffuse. In the electron micrograph, a thin layer of gold was sputtered on the sample to mitigate charging effects.

  • Fig. 4 Spectral images and video.

    (A) Schematic of measurement setup. (B) Images with filter array retracted (left) and inserted (right). (C) Normalized image array. Colored outlines indicate RGB channel assignment for false-color images in (E). (D) Visible and (E) false-color near-infrared (NIR) images of a butterfly wing (left), Euro banknote (center), and marker pen lines (right). (F) Datacube (left) constructed from image array in (C), horizontal and vertical cross sections of datacube (center), and line cuts (right) for corresponding points of interest indicated in datacube, showing spatially variant spectral response. (G) Still images captured from spectral video of pouring water. Each row shows a different channel and each column a different time in 1-s increments. Photo credit: Andrew McClung, University of Massachusetts Amherst.

Supplementary Materials

  • Supplementary Materials

    Snapshot spectral imaging with parallel metasystems

    Andrew McClung, Sarath Samudrala, Mahsa Torfeh, Mahdad Mansouree, Amir Arbabi

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