Transmission efficiency greater than 1?

iqnloiqnlo Member Posts: 12

Hi All

I just got an unbelievable result when I was doing the propagation sweep in EME solver. The S12^2 shows that the transmission is greater than 1 and I think this is totally wrong. Because the transmission cannot be greater than 1.

The S21^2 is 99% which looks fine. Can I send the project file to you somehow?




Answers

  • iqnloiqnlo Posts: 25Member

    Sorry, maybe the previous post is not clear. I'm simulating the coupling between fibre and a taper. So the port 1 is the fundamental TE mode of the fibre. And the port 2 is the end of taper.

  • gsungsun Posts: 1,651Ansys Employee

    Since this happens at smaller gap, it might be related to mesh size. Please use mesh size that can well resolve the gap.

    From the curves, they are not smooth. It may indicate that the simulation time is not long enough, autoshutoff min level is to high. Please increase simulation (setting), reduce the autoshut off level.

    In addition, it might be also due to PML reflection. Make sure the PML has about half wavelength thick, usually by increasing the number of layers. If it has larger angle incidence of the em wave, you may use SteepAngle PML with enough thickness.

    If the result does not improve, please post some screenshots directly so to help us diagnose.

  • iqnloiqnlo Posts: 25Member

    Hi!

    Thanks a lot for your reply!

    May I ask how to do this setting? "Please increase simulation (setting), reduce the autoshut off level."

    Also, what's the meaning of "PML has about half wavelength thick"? The thickness is from where to where?

  • gsungsun Posts: 1,651Ansys Employee

    simulation time setting:

    Autoshutoff min

    PML thickness is the orange colored enclosure of the simulation volume:


    you van use the "Ruler" to roughly measure it, or calculate it if you know how to get the mesh size, as you know the number of layers:


    It seems you are new to FDTD. Please watch some edu videos online:


    https://support.lumerical.com/hc/en-us/sections/360007813194-FDTD100-List-of-videos

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