Fourth-order exceptional points with spinning resonators

Investigation of exceptional points mostly focuses on the second-order case and employs the gain-involved parity-time (PT) symmetric systems. Here, we propose an approach to implementing fourth-order exceptional points (FOEPs) using directly coupled optical resonators with rotation. On resonance, the system manifests FOEP through tuning the spinning velocity to targeted values. Eigenfrequency bifurcation and enhanced sensitivity for nanoparticle have been presented. Also, near FOEP, nonreciprocal light propagation exhibits great boost and dramatic change, which may be applied to high-efficiency isolators and circulators.