  A frequency domain model of multimode circular microresonators for filter
applications in integrated optics is investigated. Analytical basis modes of 2D
bent waveguides or curved interfaces are combined with modes of straight
channels in a spatial coupled mode theory framework. Free of fitting
parameters, the model allows to predict quite efficiently the spectral response
of the microresonators. It turns out to be sufficient to take only a few
dominant cavity modes into account. Comparisons of these simulations with
computationally more expensive rigorous numerical calculations show a
satisfactory agreement.
