Discrete interband mutual focusing in nonlinear photonic lattices
  We study nonlinear coupling of mutually incoherent beams associated with different Floquet-Bloch waves in a one-dimensional optically-induced photonic lattice. We demonstrate experimentally how such interactions lead to asymmetric mutual focusing and, for waves with opposite diffraction properties, to simultaneous focusing and defocusing as well as discreteness-induced beam localization and reshaping effects. 
Christian R. Rosberg, Dragomir N. Neshev, Andrey A. Sukhorukov,   Wieslaw Krolikowski, and Yuri S. Kivshar