Surface lattice solitons in saturable nonlinear media driven by the quadratic electro-optic effect

We study theoretically surface lattice solitons driven by quadratic electro-optic effect at the interface between uniform media and an optical lattice with or without a defect. The surface defect of optical lattice strongly affects the surface soliton properties. Surface solitons originating from a positive defect can be formed in the semi-infinite and first bandgap, negative surface solitons exist in finite bandgap but are absent in the semi-infinite bandgap. These solitons associated with different bandgaps possess different stability properties. It is also shown that, as the propagation constant increases, these positive surface solitons can laterally drift toward the optical lattice and the uniform medium in the semi-infinite and first bandgap, respectively. Moreover, for a better comparison, the surface solitons and their stability at the interface between uniform media and a uniform photonic lattice are also examined in detail.