Reply To: FDTD:: simulation of directional coupler

[Guilin Sun]

Diverging: when you reduced mesh size, did you increase the number of PML? the total thickness takes effect for efficient absoprtion. 

VarFDTD uses equivalent refractive index from the slab mode, so its mesh can be coarser.

Conformal mesh 0 is good to use. COnverging testing is another thing.

You could use carser mesh in PML region if necessary. It can cause minior reflection.

If diverging is not causes by dt factor with metal BC testing, no need to change it. The standing wave pattern is due to PML refelction. Stabilized PML does not mean it can efficiently absorb light. Actually it has larger reflection. It is better to use more number of PML layers with standard PML. Or you can use custom PML with parameters from the standard PML but only increase the max layer number.

Diverging can be caused by many different issues. So please try to resolve the diverging issue by following the suggestions in the post.