Broadband optical nonreciprocity via nonreciprocal band structure

As a promising approach for optical nonreciprocity without magnetic materials, optomechanically induced nonreciprocity has great potential for all-optical controllable isolators and circulators on integrated photonic chips. However, as a very important issue in practical applications, the bandwidth for nonreciprocal transmission with high isolation has not been fully investigated yet. In this study we first review the nonreciprocity in a Brillouin optomechanical system with single cavity mode and point out the challenge in achieving broad bandwidth with high isolation. To overcome this challenge, we propose a one-dimensional optomechanical array to realize broadband optical nonreciprocity via nonreciprocal band structure. We exploit nonreciprocal band structure induced by the stimulated Brillouin scattering with directional optical pumping and show that it is possible to demonstrate optical nonreciprocity with both broad bandwidth and high isolation. Such optomechanical lattices with nonreciprocal band structure, offer an avenue to explore nonreciprocal collective effects of both photons and phonons in different frequency regimes.