Phenomenon of switching of the sign of a wavefront dislocation in a bent few-mode optical fibre

Switching of the sign of a wavefront dislocation as a result of bending of a few-mode optical fibre is predicted and confirmed experimentally. The switching effect is based on the dependence of the phase velocities of the modes in a fibre on its bending. Mode interference at the fibre output creates a wavefront dislocation with parameters which can be controlled by the fibre shape. An increase in the fibre curvature transforms a linear dislocation into a circular one with a specific sign, back into a linear one, then into a circular one with the opposite sign, etc. The frequency of alternation of the dislocation sign, resulting from the change in the bending radius, is shown to agree with theoretical estimates.