Simulation of Slow Bloch Modes

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?

Hi @kanak

We have a topic in KX that discusses the negative quality factor issue. It looks like the way to solve it is to increase simulation time specially if you have a high Q cavity. Please take a look at it and let me know if you still have problem.


Thanks for the reply.
The problem was solved when I placed the time monitors for Q analysis far
away from the sources. I had to increase simulation time to 3000 fs to get
closer to reference Q. Thanks again…

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