Boundary conditions for silicon waveguide in MODE Solutions-Single mode transmission

I would like to ask something very important.I would like to simulate a silicon waveguide 500x220nm in MODE Solutions. I would like to export the characteristics of this waveguide to INTERCONNECT. I use the Finite Difference Eigenmode Solver. I would like to ask whether or not it is OK to use “Metal” boundaries. Could i use other boudaries ?
Also, my 500x220nm silicon waveguide has single mode transmission ? How can i check that in MODE Solutions ?

It would be fine to use metal boundary conditions since in the case of a silicon waveguide with glass cladding, the supported bound modes have fields that are well-confined in the core region and we don’t expect any radiation loss. PML boundaries can also be used, but it is typically recommended that you start by using metal boundaries and this is discussed further here:

If you are simulating an SOI waveguide, you can check the number of modes that are bound to make sure that there is only 1 supported mode at the wavelength that you are interested in. Modes are bound if the effective index of the waveguide is higher than the effective index of the slab mode. An example showing how to check if modes are bound is here: