MPB

The MIT Photonic-Bands (MPB) package is a free program for computing the band structures (dispersion relations) and electromagnetic modes of periodic dielectric structures, on both serial and parallel computers. It was developed by Steven G. Johnson at MIT along with the Joannopoulos Ab Initio Physics group.
Find MPB at: http://ab-initio.mit.edu/wiki/index.php/MIT_Photonic_Bands