Strong-coupling dynamics of frequency conversion in an optical microresonator

Nonlinear strong coupling in the frequency conversion process is an emerging field and has recently become accessible in integrated photonic platforms. Here we study the strong-coupling dynamics of second harmonic generation (SHG) in an optical microresonator. It is revealed that the nonlinear modal superposition, featuring intensity-dependent Rabi oscillation, leads to a clamped maximum SHG conversion efficiency, which can be broken through a self-injection configuration. Moreover, the nonlinear strong-coupling physics is revealed for various phenomena, including bistability, period-doubling bifurcation, and chaos. Additionally, pseudoHermitian degeneracy is found, where the synchronized resonances result in enhanced SHG efficiency. This work not only provides guidance for the implementation of high-efficiency photonic devices, but also may enrich the studies of nonlinear dynamics and non-Hermitian physics in optical microresonators.