  Numerical simulations on the evolution of step-screw and edge-screw optical
phase dislocations in bulk saturable self-defocusing nonlinear media are
presented, with emphasis on their ability to induce steering waveguides for
signal beams (pulses). Two schemes for directional coupling of such signals,
both ensuring reasonable coupling-to-cross-talk efficiency ratio, are
investigated. The parameters useful for performance optimization of the
couplers are discussed.
