Learning Forum

[tteo]

Hi everyone,

I have been trying to obtain the spectrum of a all pass microring resonator on 3D FDTD. We see a ringing effect if the simulation time is not long enough (4 ps):

[Guilin Sun]

Thank you for sharing the reference. unfortunately we are unable to read without subscription. In general, you do not need special calculation for the result, as our built-in DFT power monitor automatically gives you the transmission.
Yes, you are right that for ring-resonator type, the simulation accuracy may be comprised by simulation time. For whatever the tool /post processing, in order to convert accurately the time signal to CW, it will require that the signal decays completely. any truncation of the signal will lead to reduced DFT accuracy. This is more phenomenal for large ring resonators with high Qs. Please refer this post: /forum/discussion/25276/simulation-time-and-frequency-domain-monitors
Depending on your goal, you may get some results quick without long simulation:
1: to get Qs and resonate wavelengths, you can simulate very short time by use of Q analysis group
2: to get transmission curve without very accurate value at the resonate wavelengths, you can use apodization: Understanding time apodization in frequency domain monitors
The accurate transmission at resonance will need much longer simulation time, as each round trip will contribute to the magnitude of the fields and thus the power.