Initially I have been characterizing my waveguide in a mesh window fully covered in cladding. Currently I am trying to deduce the leakage of my waveguide loss towards the slab waveguides, which are isolated by the trenches of the waveguides. Expected distances for good operation is a 3-6 um trench width.
However, the modes that I found earlier in my fully-clad mesh window dissapear when I place the new slab waveguides in the window. The mesh boundaries are PML. I don’t see a reason why the central modes can not be found any longer. I have included these two cases as pictures. For the case where the slab waveguides are included in the mesh, no solutions can be found any longer.
Any help is greatly appreciated!