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.
Highlights
Three dimensional helical chiral metamaterials resulted in effective manipulation of circularly polarized light in the visible infrared for advanced nanophotonics
We show the first realization of a triple-helical nanowire (THN) chiral metamaterial operating as highly pure broadband circular polarizers in the visible range, fabricated by a new nanotechnology method that combines the basic principles of tomography with the focused ion beam-induced deposition (FIBID) technique and that we named tomographic rotatory growth (TRG)
According to the optical properties envisaged in previous theoretical work[20,25], the realized THN samples enable optical multifunctionalities in the visible spectral range owing to the co-existence of intrinsic chirality and threefold rotational symmetry, namely giant broadband circular dichroism (CD) up to 37% and high S/N ratio in the visible range because of the low light circular polarization conversion
Summary
Three dimensional helical chiral metamaterials resulted in effective manipulation of circularly polarized light in the visible infrared for advanced nanophotonics 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. The presence of a network of multiple interconnected helical wires with opposite handedness provides 3D chirality in the visible range[17], which has been explained by a simplified 3D-oriented helical metamaterial model[18,19] These results suggest further exploitation of this chiral geometry towards the achievement of additional, integrated, chiro-optical properties such as broadband circular dichroism (CD) in the visible range, high signal-to-noise (S/N) ratio (to preserve the polarization state of the transmitted light) and high optical activity. The developed TRG represents a viable method for the realization of new versatile miniaturized devices for nanophotonics, quantum optics and biological applications
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