Nondifractive Propagation of Light in Photonic Crystals
  We show that diffraction of electromagnetic radiation (in particular of a visible light) can disappear in propagation through materials with periodically in space modulated refraction index, i.e. photonic crystals. In this way the light beams of arbitrary width can propagate without diffractive broadening and, equivalently, arbitrary light patterns can propagate without diffractive smearing. 
K. Staliunas, R. Herrero