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 on the graded-index multimode fiber (GIMF) as saturable absorber, and propose the use of varying gain levels by doubling gain fiber length to mitigate the technical difficulty of multimode fiber as a saturable absorber in the length accuracy requirements. It provides a more flexible solution to achieve a highly stable mode-locked fiber laser based on GIMF. By analogy to dispersion management, we refer to this scheme as gain management. By adopting the two mechanisms of flexible GIMF length and gain management simultaneously, a stable mode-locked pulse train with the 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 when increasing the pump power. The proposed gain management method opens a promising way for practical highly stable mode-locked technology based on nonlinear multimode interference mechanism.