Symmetry Breaking of Counter-Propagating Light in a Nonlinear Resonator

TL;DR

This paper demonstrates non-reciprocal transmission and spontaneous symmetry breaking in dielectric microresonators caused by Kerr-nonlinearity, enabling potential applications in optical switching and sensing without magnetic effects.

Contribution

It reveals how Kerr-nonlinearity induces symmetry breaking and non-reciprocity in dielectric microresonators, a fundamental mechanism for optical non-reciprocal devices.

Findings

Observation of non-reciprocal transmission in microresonators

Resonance frequency splitting allows circulation of only one counter-propagating wave

Symmetry breaking leads to transition from standing to traveling waves

Abstract

Light is generally expected to travel through isotropic media independent of its direction. This makes it challenging to develop non-reciprocal optical elements like optical diodes or circulators, which currently rely on magneto-optical effects and birefringent materials. Here we present measurements of non-reciprocal transmission 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) light waves to circulate in the resonator. Equivalently, the symmetry breaking 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. This effect is expected to take place in any dielectric ring-resonator and might constitute one of the most fundamental ways to induce optical non-reciprocity. Our findings pave the way for a variety of applications including all optical switching, nonlinear-enhanced rotation sensing, optically controllable circulators and isolators, optical flip-flops for photonic memories as well as exceptionally sensitive power and refractive index sensors.