Mode-locked Yb-doped fiber laser with graded-index multimode fiber as saturable absorber with gain management

We experimentally demonstrate a novel, linear-cavity mode-locked Yb-doped fiber laser based onthe graded-index multimode fiber (GIMF) as saturable absorber, and propose the use of varyinggain levels by doubling gain fiber length to mitigate the technical difficulty of multimode fiber asa saturable absorber in the length accuracy requirements. It provides a more flexible solution toachieve a highly stable mode-locked fiber laser based on GIMF. By analogy to dispersion man-agement, we refer to this scheme as gain management. By adopting the two mechanisms offlexible GIMF length and gain management simultaneously, a stable mode-locked pulse train withthe repetition rate of 10.96 MHz and pulse duration of ~83.4 ps at 1064.07 nm was generated.Stable pulse bunches with pulse numbers up to 12 in a single bunch were obtained whenincreasing the pump power. The proposed gain management method opens a promising way forpractical highly stable mode-locked technology based on nonlinear multimode interferencemechanism.