Interactions between spatial screening solitons propagating in opposite directions

Collision between solitons is perhaps the most fascinating feature of soliton phenomena, because the interacting self-trapped wave packets exhibit many particlelike features. Over the years, soliton collisions have been extensively studied theoretically and experimentally, in Kerr and saturable nonlinear media, revealing a variety of effects. Among these are elastic and inelastic collisions, fusion, fission, annihilation, spiraling, and more (for a review see Ref. 1 and references therein). Until recently, all experimental and theoretical work on soliton interactions treated solely solitons propagating in the same general direction, that is, solitons propagating at a small (paraxial) angle with respect to each other. A recent series of papers, however, presented theoretical studies of incoherent2–4 and coherent3,4 interactions between solitons propagating in opposite directions, for the generic Kerr nonlinearity3 as well as for the screening nonlinearity in centrosymmetric2 and noncentrosymmetric photorefractive media.4 (See Ref. 3 for a detailed explanation of coherent and incoherent interactions between solitons propagating in opposite directions.) Independently of these theoretical studies, Kip’s group has performed pioneering collision experiments with solitons propagating in opposite directions in photorefractive waveguides, demonstrating all-optical switching and routing.5,6 In this paper we present an experimental and theoretical study of interactions between one-dimensional photorefractive screening solitons propagating in opposite directions. We have found that the interaction between photorefractive solitons propagating in opposite directions suppresses the self-bending effects of both beams, leading to attraction for one beam and repulsion for the other. We have studied both coherent and incoherent interactions but did not observe differences in the overall interaction effects.