Thank you for your reply! I did the following work according to you instructions：
1. First I check the mode profile of mode source as shown below, FDTD and mode source field are set to be 2 micrometers larger than the waveguide so I think there’s no truncation?
2. I set a power monitor at the end of propagation to see T, basically it’s the same as result from time monitor.
3. I set the "frequency dependent profile" in mode source and tried 10 to 20 frequency points, but the loss is still there as before.
4. I also set a movie monitor on XOY plane to check the pulse shape in propagation, but in the video it looks like a plane wave and tranmitt to both directions???
The results are really confsing, what else can I do? Looking forward to your reply!
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