Anisotropic EME bends

[FilipeFcp]

Hi guys,

These are the results and a sketch of an example notebook. The final formatting and text were mainly done with Claude Code, with some guidance. I think it looks reasonable.

I think we should wait for the next API release before publishing this right? So I will remove the solver version part latter.

[caseyflex]

This is great! I love the convergence plot. Thanks for finding the bug and helping address it.

• We should note at the top that the entire notebook is a bit expensive to run
• I updated the solver and added a flag EMEModeSpec.bend_medium_frame which controls whether the rotation is applied to the material tensor. The default value will capture the behavior from this notebook which is a change in the EME solver behavior and matches FDTD. However the user has the option to change it to co_rotating if they are imagining bending a fiber for example, and they want the tensor to already be defined in the co-rotating frame. Maybe you could take a look at this flag and the docstrings, and echo some of that in this notebook, making that flag explicit too?

[caseyflex]

I wonder if there is a better way to use mode sorting / filtering to find the well-guided quasi-TE mode, which could be cleaner than just taking the max transmission

[caseyflex]

Actually it would be excellent to explicitly show the permittivity tensor somewhere along the bend for both cases of bend_medium_frame. So we can have a very explicit discussion of the two use cases

[momchil-flex]

Really nice verification thanks @FilipeFcp ! I don't have much to say beyond Casey's comments. Maybe no need to run 20 cells as the convergence seems pretty clear already beyond like 4.

Actually it would be excellent to explicitly show the permittivity tensor somewhere along the bend for both cases of bend_medium_frame. So we can have a very explicit discussion of the two use cases

Is PermittivityMonitor supported in some way in EME? But generally yeah I think this is a good idea, maybe take a 3-cell simulation and plot the diagonal components of the permittivity at the 3 locations. Or even plot eps_xx, eps_xy, eps_xz (first row of the tensor) to show how it becomes tensorial in the "lab" frame and just stays the same in the "co-rotating" frame.

[caseyflex]

Permittivitymonitor is fully supported in eme . Or you can probably use sim.epsilon, and you even get subpixel if tidy3d-extras is installed!