Kyle
Ansys Employee

If you would like to calculate the S matrix for both the fundamental TE and TM modes you can select the "fundamental TE and TM mode" mode selection option for the ports:

Don't use symmetry boundary conditions with this option so the solver can find both the fundamental TE and TM modes. For a 1x2 MMI this will calculate a 6x6 S matrix because there are 3 ports with two modes each.