Chirality symmetry breaking (CSB) in Kerr nonlinear whispering-gallery-mode (WGM) microcavities is essential to advance nonlinearity-based nanophotonic devices. Normally, a high chirality in such platforms usually requires a high input power. However, a high input power will induce complicated nonlinear responses that may in turn weaken the chirality. Here, we propose a CSB strategy based on the Kerr nonlinearity, in which the add-drop microring (ADM) is driven by a dual-mirror system. The linear and nonlinear mode dynamics of the clockwise and counterclockwise modes in the microring are described by coupled mode theory. Both the total intracavity energy and the energy imbalance in the proposed configuration with bidirectional inputs can be synchronously varied by the reflection amplitudes and phase delays of the dual-mirror system. It is found that the input power threshold required to excite chiral states can be effectively reduced. Meanwhile, a higher chirality can be achieved under the same level of input power compared with a mirror-free ADM configuration. Furthermore, the proposed strategy can be potentially applied to nanoparticle sensing with robustness, higher sensitivity, and a broader operational power range. In addition, the low power thresholds of the multistage CSB and the distribution of exceptional points in the proposed configuration are also analyzed. The theoretical results are expected to be further applied to high-performance sensors and other low-power on-chip photonic devices.

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• Optical microcavities
• Waveguides