Defect solitons supported by two-dimensional lattice potentials in biased centrosymmetric photorefractive crystals with saturable self-focusing nonlinearity

We investigate the defect solitons (DSs) in square photonic lattices in biased centrosymmetric photorefractive crystals with saturable self-fousing nonlinearity. We reveal the existence and stable regions of DSs due to the changing defect strength; in particular, DSs appear to be unstable in the first bandgap with high power where the repulsive defect is, which is usually stable in non-centrosymmetric media. The DSs existence and stable regions reduce with the increase of the attractive defect strength in the semi-infinite bandgap. For a repulsive defect, DSs can be profoundly affected by their defect potentials and power. (paper)