The results of the CMT approach are compared with Finite Difference Time Domain (FDTD) simulations [55]. We apply an own implementation [95,57] based on a simple second order Yee scheme [94]. Perfectly Matched Layer (PML) boundary conditions enclose the rectangular computational window, where fields are excited using the total-field / scattered field formulation. In order to generate reference signals for purposes of normalization, all FDTD calculations are carried out twice, once for the entire microresonator structure, then for one of the constituent straight waveguides only. To evaluate the spectral throughput- and dropped power, the time evolutions of the fields at suitable cross section lines through the respective ports are Fourier transformed, then projected onto the outgoing frequency domain mode profiles associated with the port. The ratio of the absolute values of these spectral signals (calculation for the microresonator structure / reference calculation) forms an approximation for the normalized output powers.
For a comparison with literature results, we consider structures as in Ref. [56], where microring/microdisk with high index contrast and very small radius resonators are calculated by 2-D FDTD with PML boundary conditions.