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Composite functional metasurfaces for multispectral achromatic optics

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ABSTRACT

Nanostructured metasurfaces offer unique capabilities for subwavelength control of optical waves. Based on this potential, a large number of metasurfaces have been proposed recently as alternatives to standard optical elements. In most cases, however, these elements suffer from large chromatic aberrations, thus limiting their usefulness for multiwavelength or broadband applications. Here, in order to alleviate the chromatic aberrations of individual diffractive elements, we introduce dense vertical stacking of independent metasurfaces, where each layer is made from a different material, and is optimally designed for a different spectral band. Using this approach, we demonstrate a triply red, green and blue achromatic metalens in the visible range. We further demonstrate functional beam shaping by a self-aligned integrated element for stimulated emission depletion microscopy and a lens that provides anomalous dispersive focusing. These demonstrations lead the way to the realization of ultra-thin superachromatic optical elements showing multiple functionalities—all in a single nanostructured ultra-thin element.

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Chromatically corrected three-layer metasurface lens.Measured light focusing with conventional FZP (a) and metasurface FZP (b) under white light illumination (Xenon arc lamp, contrast normalized for viewing purposes). Chromatic aberration is apparent in a while the focal spot at 1 mm appears white in b. Images of the focal region for a conventional FZP illuminated by laser light at 450 nm (c), 550 nm (d) and 650 nm (e) and for the metasurface FZP (f–h), showing the aberration correction for the latter. (i) Theoretical calculation (equation 2) of the focal distance for a conventional FZP (red line) and the measured focal points at the RGB wavelengths of the conventional FZP (crosses) and metasurface FZP (circles). (j) Demonstration of colour imaging using the fabricated metasurface FZP element.
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f3: Chromatically corrected three-layer metasurface lens.Measured light focusing with conventional FZP (a) and metasurface FZP (b) under white light illumination (Xenon arc lamp, contrast normalized for viewing purposes). Chromatic aberration is apparent in a while the focal spot at 1 mm appears white in b. Images of the focal region for a conventional FZP illuminated by laser light at 450 nm (c), 550 nm (d) and 650 nm (e) and for the metasurface FZP (f–h), showing the aberration correction for the latter. (i) Theoretical calculation (equation 2) of the focal distance for a conventional FZP (red line) and the measured focal points at the RGB wavelengths of the conventional FZP (crosses) and metasurface FZP (circles). (j) Demonstration of colour imaging using the fabricated metasurface FZP element.

Mentions: To compare the broadband operation of the new lens to a conventional binary FZP lens, we also fabricated a conventional binary FZP (see ‘Methods' section), illuminated both lenses with white light (Xenon arc lamp), and characterized the light propagation after the lenses. Figure 3a,b shows the light propagation after the conventional FZP and the multilayer metasurfaces lens, respectively. It can be seen clearly that for the case of the conventional FZP (Fig. 3a), the focus is strongly chromatically aberrated by more than 400 μm. For the multilayer metasurface lens (Fig. 3b), on the other hand, the chromatic aberrations are corrected and a white focus is formed at 1 mm away from the lens. The background of the conventional FZP is darker since it was fabricated as transparent rings in a continuous thin film, thus blocking background illumination. Also, its dynamic range is somewhat larger than the fabricated metasurfaces-based FZP that show lower extinction compared to continuous films. In Fig. 3c–e, we show the performance of conventional FZP with laser illumination (see ‘Methods' section) at wavelengths of 450 nm, 550 nm and 650 nm, respectively, and compare to the performance of the composite metasurface for the same wavelengths (Fig. 3f–h). The perfect chromatic aberration correction of the composite metasurface at these wavelengths is clear. Figure 3i depicts the measured focal distance versus wavelength for the uncorrected and corrected lenses. This measured low spread of the wavelength-dependent focal plane, and low crosstalk between the different layers, enables our lens to perform chromatic imaging, as presented in Fig. 3j (see ‘Methods' section and Supplementary Methods).


Composite functional metasurfaces for multispectral achromatic optics
Chromatically corrected three-layer metasurface lens.Measured light focusing with conventional FZP (a) and metasurface FZP (b) under white light illumination (Xenon arc lamp, contrast normalized for viewing purposes). Chromatic aberration is apparent in a while the focal spot at 1 mm appears white in b. Images of the focal region for a conventional FZP illuminated by laser light at 450 nm (c), 550 nm (d) and 650 nm (e) and for the metasurface FZP (f–h), showing the aberration correction for the latter. (i) Theoretical calculation (equation 2) of the focal distance for a conventional FZP (red line) and the measured focal points at the RGB wavelengths of the conventional FZP (crosses) and metasurface FZP (circles). (j) Demonstration of colour imaging using the fabricated metasurface FZP element.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5382321&req=5

f3: Chromatically corrected three-layer metasurface lens.Measured light focusing with conventional FZP (a) and metasurface FZP (b) under white light illumination (Xenon arc lamp, contrast normalized for viewing purposes). Chromatic aberration is apparent in a while the focal spot at 1 mm appears white in b. Images of the focal region for a conventional FZP illuminated by laser light at 450 nm (c), 550 nm (d) and 650 nm (e) and for the metasurface FZP (f–h), showing the aberration correction for the latter. (i) Theoretical calculation (equation 2) of the focal distance for a conventional FZP (red line) and the measured focal points at the RGB wavelengths of the conventional FZP (crosses) and metasurface FZP (circles). (j) Demonstration of colour imaging using the fabricated metasurface FZP element.
Mentions: To compare the broadband operation of the new lens to a conventional binary FZP lens, we also fabricated a conventional binary FZP (see ‘Methods' section), illuminated both lenses with white light (Xenon arc lamp), and characterized the light propagation after the lenses. Figure 3a,b shows the light propagation after the conventional FZP and the multilayer metasurfaces lens, respectively. It can be seen clearly that for the case of the conventional FZP (Fig. 3a), the focus is strongly chromatically aberrated by more than 400 μm. For the multilayer metasurface lens (Fig. 3b), on the other hand, the chromatic aberrations are corrected and a white focus is formed at 1 mm away from the lens. The background of the conventional FZP is darker since it was fabricated as transparent rings in a continuous thin film, thus blocking background illumination. Also, its dynamic range is somewhat larger than the fabricated metasurfaces-based FZP that show lower extinction compared to continuous films. In Fig. 3c–e, we show the performance of conventional FZP with laser illumination (see ‘Methods' section) at wavelengths of 450 nm, 550 nm and 650 nm, respectively, and compare to the performance of the composite metasurface for the same wavelengths (Fig. 3f–h). The perfect chromatic aberration correction of the composite metasurface at these wavelengths is clear. Figure 3i depicts the measured focal distance versus wavelength for the uncorrected and corrected lenses. This measured low spread of the wavelength-dependent focal plane, and low crosstalk between the different layers, enables our lens to perform chromatic imaging, as presented in Fig. 3j (see ‘Methods' section and Supplementary Methods).

View Article: PubMed Central - PubMed

ABSTRACT

Nanostructured metasurfaces offer unique capabilities for subwavelength control of optical waves. Based on this potential, a large number of metasurfaces have been proposed recently as alternatives to standard optical elements. In most cases, however, these elements suffer from large chromatic aberrations, thus limiting their usefulness for multiwavelength or broadband applications. Here, in order to alleviate the chromatic aberrations of individual diffractive elements, we introduce dense vertical stacking of independent metasurfaces, where each layer is made from a different material, and is optimally designed for a different spectral band. Using this approach, we demonstrate a triply red, green and blue achromatic metalens in the visible range. We further demonstrate functional beam shaping by a self-aligned integrated element for stimulated emission depletion microscopy and a lens that provides anomalous dispersive focusing. These demonstrations lead the way to the realization of ultra-thin superachromatic optical elements showing multiple functionalities—all in a single nanostructured ultra-thin element.

No MeSH data available.


Related in: MedlinePlus