Mode-locked double-clad fiber laser with a carbon nanotubes saturable absorber

In this paper, the mode-locked laser pulse with a maximum power of 366 mW is achieved by using Yb-ions-doped double-clad fiber as the gain medium and single-walled carbon nanotubes (SWCNTs) as the saturable absorber (SA). The saturable absorber with a modulation depth of 27% is fabricated by spreading the well-dispersed SWCNTs on the D-shaped segment of the fiber, which is directly etched on the standard single-mode fiber by water-assisted femtosecond laser ablation. The ring-cavity structure fiber laser is fabricated based on the SWCNT-SA. The mode-locked pulse width of 93.8 fs, central wavelength of 1083.8 nm, and 3 dB bandwith of 8.6 nm at the repetition rate of 5.59 MHz are obtained in the optimized polarization state under a pump power of 4 W.