Defect solitons in one-dimensional composite optical lattices

The existence, stability and propagation dynamics of defect solitons at interfaces in one-dimensional composite optical lattices with focusing saturable nonlinearity are investigated numerically and analytically. Solitons show unique properties with the change of defect intensity. For a positive defect, the surface solitons only exist in the semi-infinite gap, and are stable at lower power but unstable at high power. For a negative defect, the surface solitons exist not only in the semi-infinite gap, but also in the first gap; the surface solitons show rich characteristics of instability in the entire semi-infinite gap.