Surface defect lattice solitons in photovoltaic-photorefractive crystals

We report that surface defect lattice solitons (SDLSs) can be supported at the interface between the photonic lattices with a defect and the uniform photovoltaic-photorefractive (PP) crystal. We show that these SDLSs exist only in the semi-infinite gap when the defect is positive and both in the semi-infinite gap and the first gap when the defect is negative. For a positive defect, SDLSs are stable in the high and low power regions and unstable in the moderate power region. For a negative defect, SDLSs in the semi-infinite gap are stable in the moderate power region and unstable in the high and low power regions. In the first gap, SDLSs are stable in the all power regions. We find that the stable region of SDLSs increases with the positive defect strength and decreases with an increase in the negative defect strength and the power of SDLSs decrease with an increase in the positive defect strength and increase with the negative defect strength.