Coupled mode theory for modeling microring resonators

A method for the design of waveguide-coupled microring resonators is described based on an improved coupled mode theory (CMT) approach. Characteristic parameters including coupling efficiency and Q factor are theoretically analyzed. The effects of variations in the refractive index, waveguide width, bus-to-ring gap spacing, and ring radius are investigated. The accuracy of this model is evaluated by comparing its predicted calculation results to those of the numerical beam propagation method (BPM) and finite difference time domain (FDTD) simulations obtained using commercial software. The predictions of the model agree well with the simulation results.