  Subwavelength plasmonic waveguides show the unique ability of strongly
localizing (down to the nanoscale) and guiding light. These structures are
intrinsically two-way optical communication channels, providing two opposite
light propagation directions. As a consequence, when light is coupled to these
planar integrated devices directly from the top (or bottom) surface using
strongly focused beams, it is equally shared into the two opposite propagation
directions. Here, we show that symmetry can be broken by using incident
circularly polarized light, on the basis of a spin-orbital angular momentum
transfer directly within waveguide bends. We predict that up to 94 \% of the
incoupled light is directed into a single propagation channel of a gap plasmon
waveguide. Unidirectional propagation of strongly localized optical energy, far
beyond the diffraction limit, becomes switchable by polarization, with no need
of intermediate nano-antennas/scatterers as light directors. This study may
open new perspectives in a large panel of scientific domains, such as
nanophotonic circuitry, routing and sorting, optical nanosensing, nano-optical
trapping and manipulation.
