Prediction and experimental observation of crossover to discrete beam focusing in waveguide arrays with defocusing nonlinearity.

Abstract: We predict a sharp crossover from nonlinear self-defocusing to discrete self-trapping of a narrow Gaussian beam with the increase of the refractive index contrast in a periodic photonic lattice. We demonstrate experimentally nonlinear discrete localization of light with defocusing nonlinearity by single site excitation in {{LiNbO}$_3$} waveguide arrays.

Keywords: spatial solitons; diffraction; lattices

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