Controllable multiple-pulse dynamic patterns in the mode-locking ultrafast laser with a GIMF-YDF-based saturable absorber

• The GIMF-YDF structure was used as the SA in a mode locked fiber laser. • The harmonically mode-locking (HML) pulses and bunched pulses could be obtained. • The HML pulses with pulse width of 105 ps and bandwidth of 0.093 nm were realized. An Yb-doped mode-locked fiber laser with controllable multiple-pulse dynamic patterns is experimentally demonstrated by use of an all-fiber saturable absorber (SA) based on graded index multimode fiber (GIMF)-Yb-doped fiber (YDF) structure. In addition to stable fundamentally mode locked pulses with 11 MHz, multi-pulse patterns operated in bunched pulses could be obtained with different pump powers. Besides, harmonically mode-locked pulses with pulse width of 105 ps and bandwidth of 0.093 nm are realized. The harmonically mode-locking operation exhibited a high stability and worked at a wide range of pump power. To our knowledge, this is also the first report of both harmonically mode-locked pulses and bunched pulses in a fiber laser with a GIMF-YDF based SA. The results reveal the versatility and flexibility of the GIMF-YDF structured device in controlling the pulse dynamics for different experimental requirements.