Limitations of Coupled Mode Theory to model coupled microresonators “dark states”

In this work we present analytical and experimental results indicating that Coupled Mode Theory, unlike the Transfer Matrix Method, may have limitations in predicting the behavior of photonic molecules based on embedded coupled microring cavities. We show that this resonant mode-based approach fails to provide the correct transmission spectrum for some important coupled cavity configurations, although correctly predicting the existence of these modes as eigenstates of the coupled system. The measured transmission spectrum of a CMOS compatible tunable photonic molecule is used to demonstrate this limitation.