Reply To: Edge Coupler SiN waveguide to SMF fiber Strange Field Problem

[Guilin Sun]

It seems PML reflection plays role here, as the main pulse signal has already passed the interface.

Since you only want to get the coupling efficiency between the fiber and the taper end, you only need to simulate short distance around the interface. No need to include long fiber and long taper. Please check the taper mode fiels near its end and see if higher order modes are excited. Even if they are excited, you can import them as a whole to be the excitation source. By this way the simulation volume is greatly reduced so you can use much thicker PML, eg more PML layers. There is no resonance at such interface, so short simulation time should be fine. 

It is obvious that the right side PML has issues. and seems the fields have "difficulty" to propagate. The simulation will diverge evetually.

When the source is imported with broadband data, it needs time to prepare the actual signal. It also takes time for signal starting from zero to its peak value. You have offset time period at the source, which should be since the signal should not start abruptly.

The imported broadband source will take much longer time if you choose too many frequency points. Usually 20 to 30 should be enough.

Make sure you really need such broadband source.