At the ECIO Conference in Cambridge, U.K., April 2010 Photon Design presented a paper describing the simulation of ring resonators using FIMMPROP and PICWave.

The Finite-Difference Time-Domain (FDTD) method is the most commonly used methodology for modelling smaller MicroRing Resonators but although FDTD is efficient in modelling MRRs of small dimensions, long computation times and large memory requirements arise when dealing with microring resonators of larger radii.

The paper details how to accurately model large ring resonators accurately and efficiently compared to FDTD.

Accurate Design of Optical Microring Resonators
Abstract — In this article we present and test a model for large microring resonators based on implementation of the bidirectional Eigenmode Expansion Method for rigorous modelling of vectorial field propagation in the coupling region and using accurate solutions for the bend mode propagating in the ring.