title: Effects of the near-dipole-dipole interaction on gap solitons in resonantly absorbing gratings.
abstract: Gap solitons can exist in a periodic refractive-index grating modified by periodic layers of near-resonant two-level systems. In this work, we include the effect of the density-dependent near-dipole-dipole (NDD) interaction in order to generalize this model. For certain values of the grating parameters, we find that the NDD interaction significantly modifies the frequency bands in which gap solitons can exist. The difference between the model with and without the NDD interaction is discussed. The stability of gap solitons is studied numerically.