I have been trying to simulate slow bloch modes in Si photonic crystals for benchmarking a literature. The reference file is given here.
Basically, these are Si nanorods embedded in SiO2 environment. the bandstructure looks ok as shown in the reference article(please refer to fig. 1 for reported bandstrutcure). The file is attached:
planar3D_SBM_Bandstructure.fsp (1.2 MB)
Next, I tried to find the quality factor of the modes. I used the following file and high Q analysis group. planar3D_SBM.fsp (424.8 KB)
I am getting negative Q in this case. I have tried with increased meshing, changing FDTD boundary conditions and changing the size of the simulation region. However, the Q remains negative all the time.
Can you please suggest what might be the possible reason for this?