mode analysis question

Hi All,

Recently I am trying to setup a model that can find the waveguide mode that we expected to exist in a special geometry (which has been illustrated in the ppt file).

basically, the upper space are infinite air, with an infinite slab of dielectric, and the bottom is a thick layer of Au, a narrow slot has been made to create a channel in the Au.

I am looking for a waveguide mode in the slot. right now I am using the PML boundaries. but it looks like the pml didn't work very well, it has some reflections. and I was told that within the same pml layer, the materials should be identical. I just don't know if the model that i set is reasonable or not.

I attached both the mph and ppt file together.

really appreciate the help.

Thanks,
Runyu