Figure 1: Nonlinear interaction between counter-propagating light.
From: Symmetry Breaking of Counter-Propagating Light in a Nonlinear Resonator
(a) Principle of Kerr-nonlinearity-mediated interaction between counter-propagating light without a resonator. Two counter-propagating but spatially overlapping light waves (offset in the diagram for clarity) with identical frequency will experience a different effective refractive index change ∆n depending on their powers (PA, PB). The light wave with lower optical power (PB) experiences a stronger refractive index increase, which leads to a shorter wavelength. (b) Bi-directional pumping of a whispering gallery resonator at low power, generating a standing wave. When increasing the power, the system collapses either into state (c) with clockwise propagating (CW) light or state (d) with counterclockwise (CCW) propagating light. This symmetry breaking goes along with a resonance frequency splitting between the counter-propagating optical modes (shown in the lower part of panels (b–d) where the black line denotes the pump frequency). (e) Symmetry breaking shown by the splitting between the CW and CCW resonance frequencies with increasing power. (f) Fused silica resonator and tapered fibre used in the experiments (highlighted with red laser light).
