Dark solitons in dual-core waveguides with dispersive coupling.

We report on new types of two-component one-dimensional dark solitons (DSs) in a dual-core waveguide model with normal group-velocity dispersion and Kerr nonlinearity in both cores, the coupling between which is also dispersive. In the presence of the dispersive coupling, quiescent DSs supported by the zero-frequency background are always gray, being stable with the out-of-phase background, i.e., for opposite signs of the fields in the cores. In contrast, the background with a nonzero frequency supports quiescent black solitons which may be stable for both out-of-phase and in-phase backgrounds, if the dispersive coupling is sufficiently strong. Only DSs supported by the out-of-phase background admit an extension to the case of nonzero phase mismatch between the cores.