Microresonator Isolators and Circulators Based on the Nonreciprocity of the Kerr Effect

Nonreciprocal light propagation is important in many applications, ranging from optical telecommunications to integrated photonics. A simple way to achieve optical nonreciprocity is to use the nonlinear interaction between counterpropagating light in a Kerr medium. Within a ring resonator, this leads to spontaneous symmetry breaking, with the result that light of a given frequency can circulate in one direction, but not both, simultaneously. In this work, we demonstrate that this effect can be used to realize optical isolators and circulators based on a single ultra-high-Q microresonator. We obtain isolation of >24 dB and develop a theoretical model for the power scaling of the attainable nonreciprocity.