Chi3/Chi2 model


I tested a chi3/chi2 model for calculating nonlinear property.

I compared results between a linear case and a nonlinear case.
However, the result of the linear and the nonlinear case is different even if nonlinear coefficient is set to zero when chi3/chi2 model is used (I checked the reference material when considering chi3/chi2 model).
In linear case, for example, the resonant wavelength is 1550 nm, but the resonant wavelength in nonlinear case is 1580 nm when the third order nonlinear coefficient is 0. It should be same because the nonlinearity doesn’t exist.
I also used Kerr model. In this case the resonant wavelength is same as the linear case. So, I think I had a mistake using chi3/chi2 model.
I attach my source code file. Please review it.
Thank you.
Kerr_Chi3.fsp (2.5 MB)

Dear @kimmh1028

The problem seems to be convergence problem rather than material plugin. When you introduce nonlinear Chi3/Chi2 material, by default software uses stair case mesh for the base material of nonlinear material. However, in the linear simulations, software applies a more sophisticated conformal variant mesh. To solve this problem, you need to use very fine mesh so that conformal mesh and stair case mesh match or simply check the revert to base material for conformal mesh cells box for the nonlinear material. This is explained here and in this link.

Other than this, I used a finer mesh from FDTD mesh settings (you could use mesh overrides as well) and looks like the result of two simulations converge at ~1535 as is shown in the screenshot below:

I hope this clarifies the problem.


Thank you very much.

I solved the problem.