  Intuitively, light impinging on a spatially symmetric object will be
scattered symmetrically. This intuition can fail at the nanoscale if the
polarization of the incoming light is properly tailored. In fact, it has been
demonstrated that near-field interference can result in the unidirectional
excitation of plasmonic modes using circularly polarized light. Here we show
that linearly-polarized photons impinging on a single spatially-symmetric
scatterer created in a silicon waveguide are guided into a certain direction of
the waveguide depending exclusively on their polarization angle. Reciprocity
implies that the scatterer can also act as a two-input dielectric nanoantenna
radiating two different linear polarizations. Our work broadens the scope of
near-field interference beyond plasmonics, with applications in polarization
(de)multiplexing, unidirectional coupling, directional switching, radiation
polarization control, and polarization-encoded quantum information processing
in photonic integrated circuits.
