Research group of Dr. Yoshito Y. Tanak from The University of Tokyo made progress on nanoplasmonics and published their work on Nano Lett.
Achieving high directionality of scattered light in combination with high flexibility of the direction using nanoparticles is desirable for future optical nanocircuits and on-chip optical links. In this Letter, we demonstrate a single-element triangular nanoparticle can function as a nanophotonic polarization router that sorts the incoming photons into three different scattering directions according to their polarization direction. It should be noted that the overall volume of the single router is less than λ3/300, where λ is the incident light wavelength. This simple geometry can be fabricated by not only top-down approaches, required for the previously reported directional nanoantennas, but also bottom-up approaches, which are more facile and cost less. While the sharp tips of triangular nanoparticles have previously been used for strong localized confinement and enhancement, here we utilize the broken mirror symmetry and rotational symmetry of triangular particles to achieve polarization-dependent tridirectional side scattering. Our findings will broaden the scope of triangular plasmonic nanodevices for use in photon couplers and sorters, and chemo-/biosensors. Especially, the photon-sorting capability provides a new approach for polarimetric imaging with extremely compact device architectures.