Confinement loss calculation of PCF using PML

Hello,
I want to calculate the confinement loss of a Photonic Crystal Fiber using a perfectly matched layer, however it is still not clear how to implement this PML, my questions are what material this PML is composed of ? is it air, silica? what about its thickness?
is there any layer that should separate the PCF from PML? how much is its thickness ?
is there any special boundary conditions that should be implemented?
thanks