Principal Investigator Steven Johnson
Project Website http://ab-initio.mit.edu/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 in the Joannopoulos Ab Initio Physics group.
This program computes definite-frequency eigenstates of Maxwell's equations in periodic dielectric structures for arbitrary wavevectors, using fully-vectorial and three-dimensional methods. It is especially designed for the study of photonic crystals (a.k.a. photonic band-gap materials), but is also applicable to many other problems in optics, such as waveguides and resonator systems. (For example, it can solve for the modes of waveguides with arbitrary cross-sections.)
You can download the full source code (in ANSI C) for MPB under the free GPL license. The installation section of the manual describes how to install it; mainly, this consists of downloading and installing various prerequisites if you do not have them already.