Vertical coupling


#1

Consider this example:

Two Si waveguides on top of each other with a spacing of SiO2 and clad of SiO2. I can use FDTD to simulate coupling between the waveguides. However, Mode Solver doesn’t help. I tried following the approach outlined here: https://kb.lumerical.com/en/pic_passive_waveguide_couplers_evanescent.html

But I got stuck at the very first step as the modes found belong to either waveguide but there was no such mode where the field is in both waveguides.

Is there a limitation I am unaware of in Mode Solver, or am I doing something wrong?


#2

Hi Mohamed,
First, make sure you search for enough number of modes.
Secondly, It seems you can’t find the odd and even modes of the coupler. Probably, this means the coupling between the 2 waveguides it not strong enough. Try decreasing the edge-to-edge gap.
Next, I would recommend adding an over-mesh in the gap region.

You are welcome to upload your file to help you find what is wrong.