Discrepancy in the results between frequency domain and time domain simulation

[GuanhuiWang]

Hi, Here is a complain from a student "I am tried to design a single bus ring resonator with the following parameters: R=5 um Lc= 5.5 um Gap = 200 nm. using the items from the SIEPIC library. First I implemented the ring using { ebeam_dc_te1550 & LCML_pend_strip_1550 & ebeam_strip_waveguide}, and trying to compare the transmission using both the frequency domain and time domain but there is a great discrepancy between the two simulations as illustrated in the following file.

I increase the sample rate to get accurate results from the time domain but it doesn’t decrease the discrepancy. Kindly, can anyone inform me how can I get the same transmission from both the time domain and frequency domain simulation? In addition to that, I implement the ring just using { ebeam_dc_te1550 & ebeam_strip_waveguide} without using the bend (ONA2 circuit in the attached file). I change the length of the waveguide to be (Lc+pi*R), it is supposed to get the same response but it did not happen."

We found that the problem is due to lacking the "fractional delay" and "delay compensation" in the waveguide elements inside the ring model. Is it possible to update the models with the options enabled? Thank you!