PML Scaling factor in COMSOL 4.3

Hi,

I am doing a 3D simulation with COMSOL 4.3 to find the field distribution and the mode of a waveguide where all the cladding, the core and the substrate have different refractive index. I have implemented a PML at the end of my waveguide to avoid any back reflection in to the waveguide and any standing wave patterns which might arise due to this reflection.

But I am still having some reflection from my PML which means it is not optimized. I have tried to manually scale down at the ‘’PML scaling factor’’ option for each of the interface as:

wavelength/nguide/PML_length , wavelength/nsubstrate/PML_length and wavelength/nsubstrate/PML_length

but it didn't help. Can anyone suggest how to properly scale the PML in COMSOL 4.3 for optimized performance? Thank you very much for any help and suggestions.

esrom