The nanolens was 3D printed on top of a drop coated 80nm diametre nanowire using direct laser writing in low-index material by multiphoton polymerization. Only 80nm thick and acts as a light emitter. The new 3D design, about 6um tall by 6um in diameter, was computed to leverage both nanoscale interference antenna effects and the broadband operation of macroscopic lenses, achieving unprecedented directivity.
The paper "Broadband highly directive 3D nanophotonic lenses" published in Nature Communications reports a 3D printed nanolens (in effect a dielectric environment wrapping the nanowire emitter) that achieves directivities of 101 for point-sources, and 67 for finite-source nanowire emitters; three times that of traditional spherical lenses, with nearly constant performance over a 200nm wavelength range. Simulations attribute the main limitation in the obtained directivity to imperfect alignment of the nanolens to the nanowire beneath.
"While the structure is not resonant and the total size is multiple wavelengths, the critical features are sub-wavelength and enable effective utilization of nanophotonic interference effects to achieve large directivities over a wide bandwidth, while simultaneously improving out-coupling of light from the substrate" the researchers wrote.
The method of algorithmically designing nanolens described in the paper could be applied to other types of emitters, the authors note, significantly outperforming traditional intuition-based lens designs of the same size and material. Proven experimentally, the fabricated nanolens turned the nanowire's nearly isotropic photoluminescence emission to a narrow solid angle beam.
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