Thanks for sharing the links. They are helpful to understand some of the physics of the simulator. Nevertheless, I still have some problems when simulating simple structure like a straight waveguide. I tried to change the parameters as you did in with the ring, but still I get transmission power higher than one.
I have other questions as well. Is it advisable to use the multifrequency option with any structure? For example, when I tried to simulate a directional coupler without using the multifrequency option, the results were more reasonable.
Here you can see the transmission power from FDTD simulation without using the multifrequency option
While the transmission power from FDTD simulation using the multifrequency=1
As you can see from the second image, the value of transmission power decreases at higher wavelengths which is not reasonable. Why does this happen?