Amrita Pati
Ansys Employee

Hello Chinna,

The mode solution calculation doesn’t account for the nonlinearity of the material. In other words, the susceptibility values shouldn’t have any impact on the mode.

When you solve for the mode without using any base material, it completely ignores the susceptibilities and assumes the material to have a refractive index of 1. As a result, you see the power residing in the substrate as opposed to the non-linear material itself. This also explains the large deviation seen in the effective index values.

The best practice would be to use the desired base material, leave χ1 as 0 (as the permittivity of the base material would be automatically chosen from the Material Database) and only use χ3 values for your FDTD simulations.

Before you run your simulation, I would also suggest you to look at the permittivity/refractive index fitting from the Material Explorer. The losses you see in your last figure could be a result of improper fitting of the data. You can change the fitting parameters to obtain more accurate fitting.

For more information on fitting and Material Explorer, please refer to the following link:

For more information on convergence of non-linear simulations, please refer to this:

Thank you.