Reply To: FDTD:: simulation of directional coupler

[Guilin Sun]

You can enforce the mesh to be symmetry if the coupling center is at the symmetry point: 

Plane monitors can be at the center plane, or where you think the scattering is strong. You can extend the monitors to the inside of PML:

 

 You first need to identify what causes the diverge. You may also use a monitor monitor.