Interactions of dark solitons in one-dimensional self-defocusing media with fourth-order diffraction

We investigate dark solitons and their interactions in one-dimensional self-defocusing media with fourth-order diffraction (FOD). Anomalous FOD supports bifurcated dark solitons when the coefficient of FOD exceeds a threshold. Dark solitons are stable (unstable) against perturbations when FOD is normal (anomalous). FOD also controls flexibly interactions of well-separated parallel dark solitons, leading to the formation of bound states of parallel solitons pairs which are always repulsive in conventional local nonlinear media with standard (quadratic) diffraction.