Nonlinear photonic crystals near the supercollimation point
  We uncover a strong coupling between nonlinearity and diffraction in a photonic crystal at the supercollimation point. We show this is modeled by a nonlinear diffraction term in a nonlinear schroedinger type equation, in which the properties of solitons are investigated. Linear stability analysis shows solitons are stable in an existence domain that obeys the Vakhitov-Kolokolov criterium. In addition, we investigate the influence of the nonlinear diffraction on soliton collision scenarios. 
Zhiyong Xu, Bjorn Maes, Xunya Jiang, John D. Joannopoulos, Lluis   Torner and Marin Soljacic