Simple model for ring resonators backscatter

Waveguide backscatter affects the resonance shape and quality factor (Q) of ring resonators. Our simple analytical expression predicts how waveguide backscatter spoils the Q and results in resonance splitting. We show that the effects of backscatter depend only on the finesse of the resonator and when it can safely be ignored. Finally, we describe the effects of backscatter in low-loss cavities using simple complex Lorentzian functions.