Dynamics of bright discrete staggered solitons in photovoltaic photorefractive media

Theoretical results on spatial optical bright solitons excited in arrays of nonlinear defocusingwaveguides, that result from the photovoltaic effect in a photorefractive material, are presented. The existenceof four types of stationary discrete bright staggered solitons, on-site, inter-site, twisted inter-site, andtwisted on-site solitons, is shown both analytically and numerically, and their stability properties areinvestigated. The maximum Hamiltonian of staggered solitons with the same total power corresponds to stable modes.It is shown that for low total power the on-site mode is stable while in the high power regime the inter-site modeis stable. These results are confirmed numerically. In addition, steering properties of localized modes areinvestigated by introducing a transversal translational shift. Because of the translational symmetry betweenon-site and inter-site localized modes they are considered as two dynamical realizations of the same moving mode,and the formalism of the Peierls-Nabarro effective potential is applied to interpret the exchange between trappingand steering of these modes. This critically depends on the mode’s total power and the introduced phasedifference. On the other hand, steering of twisted inter-site and on-site localized modes is not numericallyobserved. Instead, transversal perturbation leads to a transformation of twisted modes either into a trappedon-site mode of smaller power and radiation, or into two trapped on-site modes.