Symmetric and antisymmetric soliton states in two-dimensional photonic lattices.

We study the dynamics of off-site excitation in an optically induced waveguide lattice. A single beam centered between two waveguides leads to an asymmetric beam profile as the nonlinearity reaches a threshold. When two probe beams are launched in parallel into two nearby off-site locations, they form symmetric or antisymmetric (twisted) soliton states, depending on their relative phase. A transition of intensity pattern from on-site to off-site locations is also observed as the lattice is excited by a quasi-one-dimensional plane wave.