  A standing-wave control field applied to a three-level atomic medium in a
planar hollow-core photonic crystal waveguide creates periodic variations of
linear and nonlinear refractive indexes of the medium. This property can be
used for efficient steering of light. In this work we study, both analytically
and numerically, the dynamics of probe optical beams in such structures. By
properly designing the spatial dependence of the nonlinearity it is possible to
induce long-living Bloch oscillations of spatial gap solitons, thus providing
desirable change in direction of the beam propagation without inducing
appreciable diffraction. Due to the significant enhancement of the
nonlinearity, such self-focusing of the probe beam can be reached at extremely
weak light intensities.
