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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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Complex lenses.(a) A dual-layer STED element composed of one layer designed to focus a green laser (λ=550 nm) at f=1 mm and a second spiral-shaped layer designed to focus a doughnut-shaped red laser beam (λ=650 nm) at the same focal distance. The topological charge of the spiral beam was set to l=1. (b) Obtained image at the focal plane for illumination with super-continuum source. (c,d) Corresponding element bright-field image and focal plane image as in a,b, respectively, for the case of topological charge l=4. The interference between the generated vortex beam and a background beam transmitted by the plate gives rise to the spiral-shaped vortex in b and the four lobe vortex in d. Scale bar, 35 μm (a,c) and 5 μm (b,d). See the recorded propagation of the beams in space showing their red vortex and green focusing characteristics in Supplementary Movies 1 and 2. (e) Demonstration of the functionality of a lens that was designed to show anomalous chromatic aberration of its RGB foci, which is shorter wavelengths focus before longer wavelengths (contrast was enhanced for clarity).
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f4: Complex lenses.(a) A dual-layer STED element composed of one layer designed to focus a green laser (λ=550 nm) at f=1 mm and a second spiral-shaped layer designed to focus a doughnut-shaped red laser beam (λ=650 nm) at the same focal distance. The topological charge of the spiral beam was set to l=1. (b) Obtained image at the focal plane for illumination with super-continuum source. (c,d) Corresponding element bright-field image and focal plane image as in a,b, respectively, for the case of topological charge l=4. The interference between the generated vortex beam and a background beam transmitted by the plate gives rise to the spiral-shaped vortex in b and the four lobe vortex in d. Scale bar, 35 μm (a,c) and 5 μm (b,d). See the recorded propagation of the beams in space showing their red vortex and green focusing characteristics in Supplementary Movies 1 and 2. (e) Demonstration of the functionality of a lens that was designed to show anomalous chromatic aberration of its RGB foci, which is shorter wavelengths focus before longer wavelengths (contrast was enhanced for clarity).

Mentions: Here we use the freedom to independently choose different materials and specific designs for each layer, to demonstrate an integrated STED lens, consisting of a dual layer that tightly focuses green light with a full round beam profile, and red light to a doughnut-shaped beam at the same focal spot. We used a conventional FZP configuration for the excitation focus and fabricated on top a spiral-based FZP for the depletion beam that leads to the generation of a doughnut beam at its focus47 (see also Supplementary Fig. 6). Figure 4a,c shows bright-field reflection images of two such fabricated devices, where we implement lenses with different topological charges l=1 and l=4, respectively. The performances of the fabricated devices were tested with a super-continuum laser as the illumination source (see ‘Methods' section), and the results shown in Fig. 4b,d (see also Supplementary Movies 1 and 2), are in good agreement with simulated results.


Composite functional metasurfaces for multispectral achromatic optics
Complex lenses.(a) A dual-layer STED element composed of one layer designed to focus a green laser (λ=550 nm) at f=1 mm and a second spiral-shaped layer designed to focus a doughnut-shaped red laser beam (λ=650 nm) at the same focal distance. The topological charge of the spiral beam was set to l=1. (b) Obtained image at the focal plane for illumination with super-continuum source. (c,d) Corresponding element bright-field image and focal plane image as in a,b, respectively, for the case of topological charge l=4. The interference between the generated vortex beam and a background beam transmitted by the plate gives rise to the spiral-shaped vortex in b and the four lobe vortex in d. Scale bar, 35 μm (a,c) and 5 μm (b,d). See the recorded propagation of the beams in space showing their red vortex and green focusing characteristics in Supplementary Movies 1 and 2. (e) Demonstration of the functionality of a lens that was designed to show anomalous chromatic aberration of its RGB foci, which is shorter wavelengths focus before longer wavelengths (contrast was enhanced for clarity).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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f4: Complex lenses.(a) A dual-layer STED element composed of one layer designed to focus a green laser (λ=550 nm) at f=1 mm and a second spiral-shaped layer designed to focus a doughnut-shaped red laser beam (λ=650 nm) at the same focal distance. The topological charge of the spiral beam was set to l=1. (b) Obtained image at the focal plane for illumination with super-continuum source. (c,d) Corresponding element bright-field image and focal plane image as in a,b, respectively, for the case of topological charge l=4. The interference between the generated vortex beam and a background beam transmitted by the plate gives rise to the spiral-shaped vortex in b and the four lobe vortex in d. Scale bar, 35 μm (a,c) and 5 μm (b,d). See the recorded propagation of the beams in space showing their red vortex and green focusing characteristics in Supplementary Movies 1 and 2. (e) Demonstration of the functionality of a lens that was designed to show anomalous chromatic aberration of its RGB foci, which is shorter wavelengths focus before longer wavelengths (contrast was enhanced for clarity).
Mentions: Here we use the freedom to independently choose different materials and specific designs for each layer, to demonstrate an integrated STED lens, consisting of a dual layer that tightly focuses green light with a full round beam profile, and red light to a doughnut-shaped beam at the same focal spot. We used a conventional FZP configuration for the excitation focus and fabricated on top a spiral-based FZP for the depletion beam that leads to the generation of a doughnut beam at its focus47 (see also Supplementary Fig. 6). Figure 4a,c shows bright-field reflection images of two such fabricated devices, where we implement lenses with different topological charges l=1 and l=4, respectively. The performances of the fabricated devices were tested with a super-continuum laser as the illumination source (see ‘Methods' section), and the results shown in Fig. 4b,d (see also Supplementary Movies 1 and 2), are in good agreement with simulated results.

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