Ultrafast all-anomalous-dispersion Er-doped large-mode-area fiber lasers

Ultrafast Er-doped large-mode-area (LMA) fiber lasers are demonstrated in the all-anomalous-dispersion regime. With the assistance of a home-made carbon nanotube saturable absorber, stable and chirp-free solitons are always observed for output coupling ratios (OCRs) varying from 10% to 90%, leading to the simultaneous achievement of the maximum pulse energy and minimum pulse duration at the OCR of 70%. To validate the universality of the all-anomalous-dispersion mode-locking, an all-fiber saturable absorber based on nonlinear multimode interference effect is incorporated into the LMA fiber laser cavity, which can also generate chirp-free solitons. The influences of gain fiber dispersion on solitons are numerically simulated, revealing that the dispersion consistency of fibers in the laser cavity is in favor of generating stable and chirp-free solitons even at an ultrahigh OCR. This work paves the way for ultrafast Er-doped LMA fiber lasers in the all-anomalous-dispersion regime, which provides an alternative route to further improve the stability and output pulse energy of ultrafast LMA fiber lasers, i.e. ensuring the dispersion consistency and hence enlarging the OCRs.