  The dispersion of a CROW made of photonic crystal mode-gap cavities is
pronouncedly asymmetric. This asymmetry cannot be explained by the standard
tight binding model. We show that the fundamental cause of the asymmetric
dispersion is the fact that the cavity mode profile itself is dispersive, i.e.,
the mode wave function depends on the driving frequency, not the
eigenfrequency. This occurs because the photonic crystal cavity resonances do
not form a complete set. By taking into account the dispersive mode profile, we
formulate a mode coupling model that accurately describes the asymmetric
dispersion without introducing any new free parameters.
