LMA effectively single-mode thulium doped fibre with normal dispersion at wavelengths around 2um

During the last few years, an increasing interest in Large Mode Area fibre operating around a wavelength of 2μm for high-power fibre laser applications has been observed. For most pulsed laser applications, it is desirable to operate the fibre in the normal dispersion regime to avoid the limiting effects of modulational instability (MI)/soliton formation [1]. However, it is very difficult to achieve normal dispersion in conventional step-index large mode area fibres operating around a wavelength of 2μm due to the fact that the dispersion of their fundamental mode is mainly dominated by the material dispersion of silica, which is anomalous and very high around this wavelength (e.g.: ~44ps/(nm.km) at 1930nm, cf. Fig. 1.(b)).