Measurement of nonreciprocal spontaneous Raman scattering in silicon photonic wires

We report on measurements that show the strength of the spontaneous Raman scattering in strongly confining silicon waveguides to depend significantly on the propagation direction of the amplified signal wave with respect to the pump wave. Furthermore, the strength of this nonreciprocity depends on the orientation of the waveguide with respect to the crystallographic axes. We find that when changing the orientation from ˂011˃ to ˂001˃, the Raman-induced nonreciprocity increases by almost a factor of 3.