Photonic crystal waveguide bandstructure calculation



I am trying to simulate the bandstructure of a single defect line PhC waveguide which is already reported in literature. When I place randomly oriented dipole cloud, I am observing 2 allowed modes in the bandgap which are actually even and odd modes. If that is the case, if I assign theta 0 or 90 degree, then ideally I should get either of these. But, eventhough I change theta value to 0 or 90, I do not see any difference in the bandstructure and still see 2 modes in the bandgap.
I even tried to change electric dipole to magnetic dipole to see if there is any difference in the bandstructure plotted, but in vain. I am attaching the simuation file of the same. Please help me regarding this.
vg_calcultion.lsf (3.7 KB)

custum_non_c_0_Si.fsp (325.6 KB)

Hexagonal 3D photonic crystal

I think the issue is that the z min boundary condition of the FDTD simulation region object is set to “symmetric” which forces the fields to have the corresponding symmetry across the z=0 plane so only TE modes can persist. This means that even though you are setting the orientations of the dipoles, only the TE modes will persist. To excite TM modes only, try changing the z min boundary condition to “anti-symmetric” and re-running the script file. Or, if you want to see the plot with both sets of modes, you can remove the symmetry altogether.

There’s some information about the meaning of the symmetric and anti-symmetric boundary conditions on the following page:

Photonic crystal bandgap