Subwavelength plasmonic waveguides show the unique ability of stronglylocalizing (down to the nanoscale) and guiding light. These structures areintrinsically two-way optical communication channels, providing two oppositelight propagation directions. As a consequence, when light is coupled to theseplanar integrated devices directly from the top (or bottom) surface usingstrongly focused beams, it is equally shared into the two opposite propagationdirections. Here, we show that symmetry can be broken by using incidentcircularly polarized light, on the basis of a spin-orbital angular momentumtransfer directly within waveguide bends. We predict that up to 94 \% of theincoupled light is directed into a single propagation channel of a gap plasmonwaveguide. Unidirectional propagation of strongly localized optical energy, farbeyond the diffraction limit, becomes switchable by polarization, with no needof intermediate nano-antennas/scatterers as light directors. This study mayopen new perspectives in a large panel of scientific domains, such asnanophotonic circuitry, routing and sorting, optical nanosensing, nano-opticaltrapping and manipulation.
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