Coherently coupled soliton pairs in biased two-photon photorefractive crystals with both linear and quadratic electro-optic effects

The coherent coupling of two spatial solitons propagating along the same line in biased two-photon photorefractive crystals with both the linear and quadratic electro-optic effects was investigated. It was proved that coherently coupled dark-dark and bright-bright spatial optical soliton pairs can be supported in the steady regime under appropriate conditions. These soliton pairs owe their existence and properties to the co-effects of both the linear and quadratic electro-optic effects where photorefractive effect may be enhanced, weakened or even counteracted because of the interaction of these two electro-optic effects. Moreover, the effects of the externally applied electric field, the initially phase difference and the intensity ratio of the two coherent beams on the existence conditions, properties of these spatial soliton pairs and self-deflection of coherently coupled bright-bright soliton pairs were discussed in detail, which lays the theoretic foundation for practical application of coherently coupled spatial soliton pairs.