the best way to implement the anisotropic PML

For my master degree thesis, I’m doing some simulations on photonic bandgap fibers and I would ask you information on the PML. In particular, I'd like to know which is the best way to implement the anisotropic PML condition in COMSOL.
Our COMSOL version presents "cylindrical", "cartesian" or "user define" options to set the PML.
Instead, in the Subdomain Settings menù, Physics I can set anisotropy condition for the refractive index (diagonal, symmetric or full).
Is this manner right for solve the problem? Can you help me?


Thank you very much in advance