Plans for full anisotropic χ² tensor support?

[Donghyun0427]

Hello, and thank you for developing FDTDX.

I noticed that recent updates added support for anisotropic materials, which is very helpful. I wanted to ask whether there are any plans to add support for second-order nonlinear materials with a full anisotropic χ^(2) tensor.

In particular, I am interested in materials such as lithium niobate, where full tensorial χ^(2) effects are important for simulations involving the Pockels effect, SHG, and other second-order nonlinear processes.

I could not find χ^(2) support in the current documentation or code, so I wanted to confirm:

1. Is full anisotropic χ^(2) support on the roadmap?
2. If so, is there any rough timeline?
3. Would the planned implementation support the full tensor form, rather than only a simplified or isotropic model?

This feature would make FDTDX much more useful for nonlinear photonics workflows.

Thank you.

[ymahlau]

Hi @Donghyun0427, thanks for your interest! I have started a discussion in #273 for the planned development features.

Regarding nonlinear materials, there is currently not a plan to implement this from our side in the near future. That being said, I am personally very interested in nonlinear material simulations and a long-term goal of mine is enabling this within fdtdx. But, it is a long-term goal which might take months-years to develop. So I don't want to give you any false hope that this feature will be developed soon.

We are also accepting any community contributions, so if you feel like developing this feature yourself feel free to give it a go. I can also assist with any questions. However, even that would probably only make sense after dispersive material models are implemented (#4).