Non-reciprocal Brillouin scattering induced transparency

Electromagnetically induced transparency provides a powerful mechanism for controlling light propagation in a dielectric medium, and for producing slow and fast light. Electromagnetically induced transparency traditionally arises from destructive interference induced by a non-radiative coherence in an atomic system. Stimulated Brillouin scattering of light from propagating hypersonic acoustic waves has also been used successfully for the generation of slow and fast light. However, Electromagnetically induced transparency-type processes based on stimulated Brillouin scattering were considered infeasible because of the short coherence lifetime of hypersonic phonons. Here, we report a new Brillouin scattering induced transparency phenomenon generated by acousto-optic interaction of light with long-lived propagating phonons in a silica resonator. We demonstrate that Brillouin scattering induced transparency is uniquely non-reciprocal owing to the propagating acoustic wave and accompanying momentum conservation requirement. We also show that Brillouin scattering induced transparency enables ultralow-power ultralow-footprint slow-light generation with delay-bandwidth product comparable to state-of-the-art stimulated Brillouin scattering systems.