> What boundary conditions should I use when creating simulation in MODE - FDE Solver? Should I use PML? If yes, what PML parameters should I use? Those are some typical questions and I hope that this post will help you to make the right decision.
Generally, FDE uses metal boundaries by default and that is also what is recommended when starting with a new simulation.
PML should be used only when there is a good reason for it - for example when you have radiative loss such as in bent waveguide or when you are interested in exact loss parameters. In such situations, the default PML settings should be sufficient in most cases as you do not have to worry about the numerical instability in frequency domain(as opposed to FDTD)
Here is the default PML settings:
If you find that the PML is not being completely absorbing, for examplewhen the incident light and the field is non-zero when it reaches the end of PML, then you can increase the number of layers.
You should not need to adjust the parameters kappa and sigma. Sigma is exaggerated by default(sigma=5) in FDE and kappa is related to spatial distribution of PML and the default settings kappa=1 should be usually a good option for your simulations. On contrary, making kappa too large could cause that perfectly matched layer is not matched anymore.
For detailed understanding of the PML model and the related parameters, you can read the following paper that describes the detailed meaning of each parameter and the PML concept as a whole:
S. D. Gedney and B. Zhao, An Auxiliary Differential Equation Formulation for the Complex-Frequency Shifted PML, IEEE Trans. on Antennas & Propagat., vol. 58, no. 3, 2010
Additionally, you might notice that compared to FDTD, the parameter alpha is not available in FDE. The reason is that alpha is a stability factor that is not used in FDE since it is frequency domain solver.