Helical-core Yb-doped fibre laser

In this paper we report a new approach for achieving robust single-mode operation in a large-core fibre laser or amplifier by employing a core, which has a helical trajectory within the cladding material. As a confirmation of the benefits of the helical-core geometry, an Yb-doped fibre with a straight core of the same diameter and numerical aperture was tested, which yielded a multimode output beam with beam propagation factor, M/sup 2/=5.5 and /spl sim/50% of the fibre output rejected from the polariser.