Info Request - eigenmode coefficients the same for sources

[Andeloth]

I'm running simulations to try to determine how long do we need to make a waveguide before a GaussianBeamSource couples into the same eigenmode as an EigenModeSource. I'm comparing the eigenmode coefficient/power returned by get_eigenmode_coefficient at several mode monitors at different locations along a straight waveguide. However, in every simulation I ran I got that the power at each location is the same for both sources.

What causes this? Am I setting something up incorrectly or is this intended?

Also, regardless of which mode I specify for the EigenModeSource (tried band numbers 1,2,5) only mode 2 is excited.

[smartalecH]

It's hard to say without any code or even an image of the simulation (easily provided using plot2D). There's not a lot of detail about the sources themselves either...

[Andeloth]

and an image of the simulation

[Andeloth]

It seems like modes 1 and 2 are the exact same, this might be because the fundamental TE and TM modes have the same properties other than TE/TM-ness. What I'm more confused about is why the GaussianBeamSource and EigenModeSource give such similar results. I would expect them to give different results while the gaussian source hasn't coupled into the waveguide eigenmodes yet.

[smartalecH]

Your ModeSource needs to span at least some of the cladding. Your GaussianBeamSource needs to at least span the FWHM (usually much more). Your mode monitors need to span into the cladding too.

Also, in 2D, a polarized source won't excite the other polarization.

[Andeloth]

Okay, I increased all of the widths, and I got these simulations (1st gaussian beam source, 2nd eigenmode source with mode 3)

and yet the eigenmode coefficients were still only relevant for modes 1 & 2 (which are overlapping)

and the GaussianBeamSource and EigenModeSource simulations still give the exact same results.

This is what the simulation looks like now:

[Andeloth]

OH nevermind, I found a mistake in the code that caused that, it's giving me the correct results now.