Why the result of FDTD is much lower than EME?


Hi, I’m trying to simulate structure of below picture by EME and FDTD.

The below plot is the result of EME solver. It shows that for taper length over 80um, efficiency will be over 94%. While for taper length=100um, the efficiency of FDTD is 2.9%(T for monitor 3), which is much lower than EME. And the full profile is also shown below.

Could you do me a favor to help me find out the reason why the FDTD result is so low? Thank you very much. The files are attached.
taper EME.lms (403.6 KB)
taper FDTD.fsp (3.1 MB)


From the image of the field profile in the FDTD Solutions simulation, it looks like the simulation time was not long enough for the fields to propagate through the full length of the device, so the fields only propagate to the x=-10 um point by the time the simualtion ends. I would recommend editing the FDTD solver region object and increasing the simulation time setting in the “General” tab of the edit window.

Ideally, the auto shutoff threshold should be reached before the maximum simulation time is reached. There is more information about the auto shutoff and how to tell if it was reached in the following post: