Jonathan M. Silver

Symmetry Breaking of Counter-Propagating Light in a Nonlinear Resonator

Spontaneous symmetry breaking is a concept of fundamental importance in many areas of physics, underpinning such diverse phenomena as ferromagnetism, superconductivity, superfluidity and the Higgs mechanism. Here we demonstrate nonreciprocity and spontaneous symmetry breaking between counter-propagating light in dielectric microresonators. The symmetry breaking corresponds to a resonance frequency splitting that allows only one of two counter-propagating (but otherwise identical) states of light to circulate in the resonator. Equivalently, this effect can be seen as the collapse of standing waves and transition to travelling waves within the resonator. We present theoretical calculations to show that the symmetry breaking is induced by Kerr-nonlinearity-mediated interaction between the counter-propagating light. Our findings pave the way for a variety of applications including optically controllable circulators and isolators, all-optical switching, nonlinear-enhanced rotation sensing, optical flip-flops for photonic memories as well as exceptionally sensitive power and refractive index sensors.

Microresonator isolators and circulators based on the intrinsic 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 in both directions 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 more than 24 dB and develop a theoretical model for the power scaling of the attainable nonreciprocity.

Kerr superoscillator model for microresonator frequency combs

Microresonator-based optical frequency combs (“microcombs”) have attracted lots of attention in the last few years. The process of comb generation in microresonators can be modelled in the frequency domain using coupled mode equations [1], and has also recently been successfully described in the time domain [2] using the Lugiato-Lefever equation [3]. Though time-domain approaches [4, 5] have brought many interesting insights for the understanding of microcombs, an intuitive frequency-domain model has not yet been established.