Dissipative coupling in photonic and plasmonic resonators

The rapid progress of nanophotonics demands theoretical frameworks capable of predicting the resonant behavior of complex systems comprising constituents of varying nature, operating beyond the weak-coupling, high-Q regime where classical temporal coupled-mode theory (CMT) is applicable. We present a coupled-quasinormal-mode framework for analyzing dissipative coupling with photonic and plasmonic resonators. The framework provides rigorous closed-form expressions for dissipative coupling coefficients and introduces novel features, such as a coupling scheme via time derivatives of excitation coefficients. It delivers transparent and accurate predictions of exotic phenomena—such as zero-coupling between very close cavities and level-attraction effects—that are only vaguely captured by traditional CMT models. Efficient and user-friendly, this framework facilitates rapid parameter space exploration for device design and offers potential for extension to nonlinear and quantum systems in future applications.