Polarization Plots
Default Polarization plots are automatically generated for Periodic ports in 3D and in 2D, if the Electric field components for setting in the Components section for the physics interface is set to Three-component vector. The Polarization plot includes polarization ellipses for each diffraction order. The polarization ellipses are generated by plotting the in-plane Jones vector element versus the out-of-plane Jones vector element for a phase change of 2π.
In the COMSOL Multiphysics Reference Manual you can find more information about the Polarization plot type.
For an example model including a Polarization plot, see Hexagonal Grating: Application Library path RF_Module/Tutorials/hexagonal_grating.