Reply To: Bandstructure disagreement, FDTD vs MPB

[Guilin Sun]

"I have tried increasing the simulation time up to 10 times the original 10 000 fs, but the result remains unchanged. I am limiting the frequency to visualize only the first five bands, but in Lumerical, many more bends appear in that frequency range. "

Unfortunately, we do not know what the simulation time it will be in order to get the correct band structure. You may change simulation time and see if it improves.

MPB can easily simulate a specified polarization. However if the structure has no symmetry, FDTD will simulate all polarization.  Please make sure the meaning of TM is the same, since it can be confused with TE as the definition is not unique. But from your result, it seems the TM is correct as it shows the bandgap.

Since you have obtained satisfactory result at lower refractive index, you can gradually increase the refractive index with proper simulation time to match the other.