anna.wirth-singh
The port at the bottom of the ring itself is a bit unusual. Ports are typically placed on the input/output waveguides to the device, as you have them on the top waveguide, so I would recommend using the transmission results from the top two ports.
Nevertheless, I am glad that increasing the simulation time has resolved the issue. Since ring resonators can have a very high Q factor, very long simulations may be required in order for all the light to leave the simulation region, so the long simulation time is not too surprising. Another thing that you can try is to select the ‘stabilized’ PML profile option on the x-boundaries (see PML boundary conditions in FDTD and MODE – Ansys Optics). The stabilized PML option could be used at the x-boundaries where the waveguide intersects the boundary, while the standard PML boundaries can be used in the y-boundaries to try to reduce the simulation time. However, this is probably not necessary because there does not seem to be any indication of divergence here.Â
Additionally, we often recommend breaking up a large ring resonator like this into pieces and simulating the ring in INTERCONNECT, as shown in these examples:
https://optics.ansys.com/hc/en-us/articles/360042322794-Ring-Modulator Â
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