Triple-helical nanowires by tomographic rotatory growth for chiral photonics

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.