Unidirectional Flow of Discrete Solitons in Waveguide Arrays

We present a proposal for realizing a unidirectional flow of discrete solitons in optical waveguide arrays or coupled resonator optical waveguides. Our proposal is based on modulating the coupling coefficients between the waveguides by two reflectionless potentials with different depths and finite separation. For a single reflectionless potential, we demonstrate numerically the possibility of nonlinear switching with a critical nonlinearity strength at which sharp transition in the transport coefficients takes place.