I am having trouble with calculating the bend loss for a waveguide; mostly, my troubles surround the convergence of the loss to a reasonable answer. In the waveguide_bend.lms file (directly downloaded from the “Bent Waveguide Analysis” page) I click “calculate modes” and observe that my BENT (r=1.5 microns) propagation loss 8.24 dB/cm.
However, if I double the number of FDE mesh cells for the x and y directions, then rerun the simulation I get a loss propagation loss of 2.72 dB/cm (a significant difference). What is going on here? Are the default settings of this example not setup to be accurate?
I’ve been adjusting the simulation region area and the number of mesh cells for this example, and it seems I can attain just about any loss imaginable (large, small, negative, positive). I hear the PML boundary conditions are necessary to absorb the radiative losses. But is there a methodical way to set the mesh and simulation area settings to ensure accurate loss calculations? Generally, it seems I’ll simply calculate less loss the further away my PML boundaries are.
I understand for the true bend loss we need to add the contributions from the overlap mismatch, which I haven’t had any problems with.