nonlinear optic effect

Hi!

I'm trying to simulate the nonlinear optic effect in wave propagation. As a result, my refractive index = n_o+n_2*(I). Because intensity I varies, I get a inhomogenous refractive index in the 2D domain. But I can only enter a constant for refractive index. I wonder if COMSOL has any tricks to solve this inhomogenous material.

Thanks,

Tina