Interaction of counterpropagating discrete solitons and nonlinear surface Tamm states in 1D waveguide arrays

We have investigated interaction of counterpropagating discrete solitons and nonlinear surface Tamm states in a one-dimensional waveguide array in photorefractive lithium niobate. While for low input powers only weak interaction and formation of counterpropagating vector solitons and Tamm states is observed, for higher input powers a growing instability results in discrete lateral shifting of solitons. Numerical modelling shows three different regimes: propagation of vector solitons at low power, instability for intermediate power levels leading to discrete soliton shifting, and irregular temporal dynamics of the two beams for high input power.