Investigation of the reabsorption effect in an all-fiberized mode-locked thulium-doped fibre laser

We investigate the influence of the reabsorption effect on pulse characteristics in an all-fiberized ultra-fast thulium-doped fibre laser system. Mode-locked operation was enabled by a semiconductor saturable absorber mirror, and the laser generated stable ultra-short pulses at a repetition rate of 11.29 MHz. By changing the length of the thulium-doped fibre, and hence the reabsorption loss, we found that the reabsorption effect had a significant influence on the optical spectrum and pulse duration of the mode-locked fibre laser. Output durations from 2.04 ps to 20.8 ps have been achieved, corresponding to operating wavelengths changing from 1968.9 nm to 2054.7 nm. Qualitative explanations of these phenomena have also been demonstrated. (paper)