Abstract

Wave propagation in nonlinear periodic systems has recently been the focus of considerable attention. In these systems, the underlying dynamics are dominated by the interplay between the linear coupling between lattice points and the on-site nonlinearity. Indeed, a balance between these effects results in a self-localized state, better known as a discrete soliton [1-4]. Such examples occur in abundance, in all branches of science, such as biological [1] and solid-state physics [2], Bose-Einstein condensates [3], and nonlinear optics [4]. In general, the dynamical behavior of these discrete systems differs substantially from that of their continuous counterparts. For example, in the optical case, a periodic array of waveguides is associated with a Brillouin zone that significantly alters its collective diffraction properties. This, in turn, leads to a host of interesting properties, e.g. anomalous ("negative") diffraction and diffraction management [5], and to in-phase and out- of-phase (staggered) [6] soliton solutions. Thus far, ID discrete linear diffraction and in-phase discrete solitons have been observed in semiconductor waveguide arrays [8]. Here, we report the first experimental observation of discrete solitons in an array of optically-induced waveguides. The waveguide arrays are induced in photorefractive crystals by interfering pairs of plane waves, and the solitons form when the screening nonlinearity is employed. We demonstrate both in-phase and staggered bright solitons in 1-D arrays and discuss recent experiments in 2D waveguide lattices. More specifically, the experiments with out-of- phase solitons constitute the first experimental observation of bright staggered solitons.

© 2002 Optical Society of America