Anomalous interaction of spatial solitons in photorefractive media

The nature of the forces between mutually coherent interacting solitons has been discussed in the literature for both temporal as well as spatial solitons [1-2]. It has been established that in the case of homogenous self-focusing media the interaction force depends on the relative phase of the solitons. In particular, two in-phase solitons attract while out-of-phase solitons repel. Phase-sensitive attraction, repulsion, and fusion of spatial solitons have been demonstrated in experiments with various nonlinear media including liquids [3], glass waveguides [4], atomic vapours [5], and photorefractive crystals [6].