Mesoscopic self-collimation and slow light in all-positive index layered   photonic crystals
  We demonstrate a mesoscopic self-collimation effect in photonic crystal superlattices consisting of a periodic set of all-positive index 2D photonic crystal and homogeneous layers. We develop an electromagnetic theory showing that diffraction-free beams are observed when the curvature of the optical dispersion relation is properly compensated for. This approach allows to combine slow light regime together with self-collimation in photonic crystal superlattices presenting an extremely low filling ratio in air. 
Julien Arlandis, Emmanuel Centeno, R\'emi Poll\`es, Antoine Moreau,   Julien Campos, Olivier Gauthier-Lafaye and Antoine Mon...
physics.optics