fieldprofile cut off (simulation of directional coupler)

hi everyone,

iam trying to simulate a directional coupler via varFDTD
and i’ve got the problem that my field profile is always cut off after a specific propagation distance,
no matter what parameters i choose (geometry of structure, mesh, boundary conditions, etc.)

the simulation is running fine until the end, i dont receive any errors.

anybody encountered a similar problem? is it maybe due low memory?
iam running the simulations on a quad-core cpu, 8GB RAM.

thanks for all your help!

directional_coupler_varFTDT_2.lms (1.3 MB)

Dear @re-fuse

I noticed that your simulation time is too short such that simulation stops before light propagates all the way along the waveguide. You can use either movie monitor to check this, or if you set the boundary conditions to PML, you will notice that autoshutoff level doesn’t drop within set simulation time (1000 fs). Here is the screenshot of the results when I increased simulation time to 5000 fs:

I attached my simulation file for your review:
directional_coupler_varFTDT_modified.lms (437.3 KB)

You can see that light couples from one waveguide to another and couples back again into first waveguide. Also, please note that in current simulation setup you will have reflections from the facet of both waveguides. Thus interpreting results will be hard and field profile in the screenshot above shows both forward propagating and backward (reflected) light.