High power all-fiber passively mode-locked thulium-doped fiber laser

A self-starting 2 m a fiber passively mode-locked Tm3+-doped fiber laser based on nonlinear loop mirror (NOLM) was demonstrated. The laser operated at a continuous wave or unstable pulses regime after reaching the launched pump power of 3 W. Self-starting mode-locked pulses centered at 2 061.5 nm with an FWHM of 18.1 nm and an average output power of 8.8 mW were achieved when the launched pump power increased to 4.69 W. Continuously increasing to the maximum launched pump power of 7.56 W, stable mode-locked pulses centered at 2 062.2 nm with a FWHM of 17.1 nm were produced at a slope efficiency of 6.2%. The pulses operated at the repetition rate of 4.26 MHz with a single pulse energy up to 65.6 nJ and a pulse width of 424 fs. To the best of our knowledge, this was the first demonstration on mode-locked fiber laser based on NOLM at 2 m region with the highest single pulse energy.