Evanescent field propagation in EME

Hi all,

In EME simulation, if the number of modes selected is larger than the number of guided modes, the EME can include evanescent modes, meaning that the neff has an imaginary part (even though the material itself is lossless).

How does EME handle the wave propagation in this case? Does it include these evanescent wave during propagation? What I can see from the individual cell information is that the S matrix element related to these evanescent waves are all zero. So I don’t know if this is indeed the physical case, or if the Lumerical solver just plain ignore all the evanescent waves when calculating the S matrix.

Thanks,
JY

Hey @yangj,

This is a good question that is interesting to consider. The FDE solver can and will find these modes, but during propagation when the EME solver calculates the coupling it will work out to be essentially zero . Therefore, we do not have to worry about them. For more information this. Please look into our EME 100 course. I think that these videos in particular will answer your question.

Regards,
-Taylor