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      Triple-helical nanowires by tomographic rotatory growth for chiral photonics

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          Abstract

          Three dimensional (3D) helical chiral metamaterials resulted effective in manipulating circularly polarized light in the visible-infrared for advanced nano-photonics. Their potentialities are severely limited by the lack of full rotational symmetry preventing broadband operation, high signal-to-noise ratio, and inducing high optical activity sensitivity to structure orientation. Complex intertwined 3D structures like Multiple-Helical Nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy.

          Here we report 3D triple-helical nanowires, engineered by the innovative Tomographic Rotatory Growth, based on Focused Ion Beam Induced Deposition. These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1000 nm), with a high signal-to-noise ratio (up to 24 dB). Optical activity up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices which can be integrated in optical nanocircuits to modulate the visible light polarization.

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          Most cited references31

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          Plasmonics: Fundamentals and Applications

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            Gold helix photonic metamaterial as broadband circular polarizer.

            We investigated propagation of light through a uniaxial photonic metamaterial composed of three-dimensional gold helices arranged on a two-dimensional square lattice. These nanostructures are fabricated via an approach based on direct laser writing into a positive-tone photoresist followed by electrochemical deposition of gold. For propagation of light along the helix axis, the structure blocks the circular polarization with the same handedness as the helices, whereas it transmits the other, for a frequency range exceeding one octave. The structure is scalable to other frequency ranges and can be used as a compact broadband circular polarizer.
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              Twisted optical metamaterials for planarized ultrathin broadband circular polarizers.

              Optical metamaterials are usually based on planarized, complex-shaped, resonant nano-inclusions. Three-dimensional geometries may provide a wider set of functionalities, including broadband chirality to manipulate circular polarization at the nanoscale, but their fabrication becomes challenging as their dimensions get smaller. Here we introduce a new paradigm for the realization of optical metamaterials, showing that three-dimensional effects may be obtained without complicated inclusions, but instead by tailoring the relative orientation within the lattice. We apply this concept to realize planarized, broadband bianisotropic metamaterials as stacked nanorod arrays with a tailored rotational twist. Because of the coupling among closely spaced twisted plasmonic metasurfaces, metamaterials realized with conventional lithography may effectively operate as three-dimensional helical structures with broadband bianisotropic optical response. The proposed concept is also shown to relax alignment requirements common in three-dimensional metamaterial designs. The realized sample constitutes an ultrathin, broadband circular polarizer that may be directly integrated within nanophotonic systems.
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                Author and article information

                Journal
                101528555
                37539
                Nat Commun
                Nat Commun
                Nature communications
                2041-1723
                11 February 2015
                18 March 2015
                2015
                18 September 2015
                : 6
                : 6484
                Affiliations
                [1 ]National Nanotechnology Laboratory-NNL, CNR-IMIP, via Arnesano, 73100 Lecce, Italy
                [2 ]Università di Roma La Sapienza, Dip. SBAI, Via Scarpa 16, 00161 Roma, Italy
                Author notes
                [* ]Correspondence and requests for materials should be addressed to V.T.. vittorianna.tasco@ 123456nano.cnr.it

                Author contributions

                M.E. conceived the original idea of the proposed fabrication method (TRG) and designed and fabricated the THN metamaterial. M.E. and V.T. supervised the experimental design and implementation. M.C. contributed to the fabrication process and SEM analysis. A.B. carried out the calculations and numerical modeling. F.T. implemented and carried out the optical measurements. D.S. supervised the optical studies. All authors discussed the results and analyzed the data. M.E. wrote the manuscript with contribution from V.T., D.S. and A.P.. A.P devised and coordinated the research activity.

                Article
                EMS62069
                10.1038/ncomms7484
                4374152
                25784379
                b894b6ff-deb4-4263-bb4f-f5c33e5f642e

                Reprints and permission information is available online at http://www.nature.com/reprints.

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