Transmission power degrade with simulation time


I am designing Si3N4 double bus ring using VarFDTD. I simulated the design up to auto-shutoff threshold. I got some transmission ripples when I simulated the design up to 15000fs time. But when I increased the simulation time, the transmission spectrum was smooth but power dropped from 0dB to 5dB.

  1. May I know why power has dropped with simulation time? I am attaching the spectrum screenshot here.
  2. How can I solve this power dropped problem?

Please give me your valuable suggestion on this. Thanks.

Hello @rifat.nazneen ,

This is strange, I don’t think I’ve seen anything similar before. Could you provide the simulation file so I could take a look?

I don’t think it would be overestimating the transmission if the simulation time was too short. What was the simulation time for the second, longer simulation? Do you have result with any other simulation times?