Self-focusing and defocusing in waveguide arrays

We show that two regimes of diffraction exist in arrays of waveguides, depe nding upon the input conditions. At higher powers, normal diffraction leads to self-focusing and to the formation of bright solitons through the nonli near Kerr effect. By slightly changing the input conditions, light experien ces anomalous diffraction and is nonlinearly defocused. For the first time, self-focusing and self-defocusing have been achieved for the same medium, structure, and wavelength.