Nanophotonics. Chiral nanophotonic waveguide interface based on spin-orbit interaction of light.

Controlling the flow of light with nanophotonic waveguides has the potential of transforming integrated information processing. Because of the strong transverse confinement of the guided photons, their internal spin and their orbital angular momentum get coupled. Using this spin-orbit interaction of light, we break the mirror symmetry of the scattering of light with a gold nanoparticle on the surface of a nanophotonic waveguide and realize a chiral waveguide coupler in which the handedness of the incident light determines the propagation direction in the waveguide. We control the directionality of the scattering process and can direct up to 94% of the incoupled light into a given direction. Our approach allows for the control and manipulation of light in optical waveguides and new designs of optical sensors.