Mode-locked ytterbium-doped fiber laser based on offset-spliced graded index multimode fibers

We developed a passively mode-locked ytterbium-doped fiber laser based on offset-spliced graded index multimode fibers (OS-GIMFs), where OS-GIMFs play the role of saturable absorbers. The modulation depth of the saturable absorber is 15.28%, which significantly improves the performance of saturable absorber by adopting offset-spliced method. A stable mode-locked pulse train at 1040 nm with a 27.32 MHz repetition rate is generated when pump power reaches the threshold. The output pulse-width is a ∼11 ps and can be compressed to 980 fs by using a pair of gratings. The fiber laser is superior in terms of low cost, high damage threshold, and easy fabrication; thus, it has potential for application in ultrafast photonics and industrial processing.