Microring Filter SImulations


Hello All,

I am simulating microring filters shown here:

I am getting a decent transmission spectrum with periodic peaks. However, I’m not seeing the widening of the passband (or dropband) as I increase the number of rings.

Has anyone else experienced this?


Dear @kar3

Can you please provide your simulation files?

Also, can you please explain the widening of the passband effect? Do you expect to see the effect with identical microrings?




Here is a paper that shows the band widening with the addition of rings…
(Figure 5)

I have attached the lms file for 3 rings…

Thanks.LiNbO3_3_rings.lms (2.5 MB)


Dear @kar3

I found an error in your simulation file. Since z-span of VarFDTD was small (1.7um), you had a discontinuity in your field along the z-direction. I increased the span to 2um and here is the screenshot of the mode profile:

Can you do the modification and run the simulation again? Generally make sure that you have enough mesh cells to resolve the gap.

Please keep me updated with your results and I am happy to help if you are confronting any further issues.



Ah! Thank you! This seems to fix the passband problem.
I really appreciate it