Enhanced mode coupling by local structuring of optical fibre cores with 800 nm femtosecond pulses

The introduction of short-pulse generation in optical fibres has generated a need for optical fibres that can carry large mode intensities without distorting the pulses. The usual way of doing this has been by extending the dimensions of a waveguide, hereby enlarging the effective areas of the modes propagating. However this offers very little spatial control of the pulses, and introduces loss in the fibre, due to coupling to less stable higher order modes. Recently, a novel type of optical fibres has been developed, that allows stable propagation of higher order modes with ultralarge modal areas. It has been shown that they can carry a higher order mode several meters without significant distortion of the mode.