I have a question about the mode expansion monitor. I got “a”, “N” and “T_forward” from the result. According to this page https://support.lumerical.com/hc/en-us/articles/360034902433, T_froward is the transmission of input field to selected mode and can be caluclated by (aout^2/Nout) / (ain^2/Nin). But I did it manually and found they are not equal actually. The file is attached. It’s the official example. All I did is just adding a power monitor “in” at input, same position as source.expansion2.fsp (398.0 KB)
So I want to ask what’s the definition of the “T_foward” from the result of expansion monitor? What’s the difference from (aout^2/Nout) / (ain^2/Nin)? If I want to calculate the s matrix from input fundamental TE to output fundamental TE, which one should I use?
One more question is that when they are used in varFDTD and the mode expansion has to be 1d, does the power monitor have to be 1d as well?
Another question is, does the position of mode expansion matter? I mean can I put it at input rather than the current position?
Thanks a lot!!!