PHENOMENON OF SWITCHING OF THE SIGN OF A WAVE-FRONT DISLOCATION IN A BENT FEW-MODE OPTICAL-FIBER

Switching of the sign of a wavefront dislocation as a result of bendin g of a few-mode optical fibre is predicted and confirmed experimentall y. The switching effect is based on the dependence of the phase veloci ties 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 si gn, back into a linear one, then into a circular one with the opposite sign, etc. The frequency of alternation of the dislocation sign, resu lting from the change in the bending radius, is shown to agree with th eoretical estimates.