Generation of bound solitons in a mode- locked Tm-doped fiber laser based on a graded-index multimode fiber saturable absorber

In this work, we report on the experimental observations of bound solitons in a Tm-doped passively mode-locked fiber laser by using an all-fiber saturable absorber, structured by a stretched graded index multimode fiber. Stable out-of-phase soliton pairs are obtained, with a temporal separation of 4.36 ps between the two ~1.88 ps pulses, while the central wavelength can be continuously tuned from 1959 nm to 1962 nm. Meanwhile, some different pulse separations from 16 ps to 18.02 ps of tightly bound soliton pairs have also been realized by cautiously adjusting the PC. The results are helpful for us to understand the nonlinear dynamics in fiber lasers and further explore high-capacity fiber communication.