  Birefringent magnetophotonic crystals are found to exhibit degeneracy
breaking for asymmetric contradirectional coupling in planar waveguides.
Fundamental to high-order local normal mode coupling leads to partially
overlapping gyrotropic bandgaps inside the Brillouin zone and partial
suppression of Bloch mode propagation. A large magneto-optically active
reorientation in polarization state is found for allowed Bloch modes at bandgap
edges.
