Dear Steven, Thanks for your MPB package. I installed your package and passed checking file test. I have some questions on calculating bands in 2-D triangular hole structure. 1) You used a rhombus shape unit cell which uses the centers of four nearby holes as the unit cell's four corners. This unit cell doesn't have any rotational symmetry. Will the result loss any symmetry property, for example, degenerate modes? I would think that using different unit cells should yield the same result. Although it might be difficult to compute the band structure, one would have rotational symmetry if one choose unit cell as a hexagonal shape with only one hole in the center. Could you please explain why your rhombus shape unit cell won't loss any symmetry property? Thanks. 2) When I used nonzero kz value with (run-te) or (run-tm), your package gave me following error message: k vector is incompatible with specified parity I read page 67 in "photonic crystals" by Joannopoulos. The book said the mirror-reflection symmetry is still intact for kz=0, TE and TM modes still decouple in in-plane propagation. Why will nonzero kz break mirror-reflection symmetry? In analogy to step index fiber, vector wave analysis does have non zero kz for TE and TM modes, right? Is there any fundamental reason TE and TM can't exist with nonzero kz? Thanks in advance for your time. Highest regards, John
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