Q-switched Noise-Like Pulse in a Tm-doped Fiber Laser

A Q-switched noise-like pulse operation was observed in a nonlinear polarization evolution based thulium-doped fiber laser. This novel phenomena formed in a noise like background. When the pump power was properly controlled and the polarization controller was carefully adjusted, a noise like mode locked pulse was modulated by a Q-switched pulse envelope, which resulted in the Q-switched noise-like pulse formation. In a single pulse envelope, there exist many mode locked pulses that have fundamental repetition rate which is corresponded to the cavity period. When the pump power was carefully increased from 760 mW to 1000 mW, the repetition rate of the adjacent pulse envelope can increased from 34 to 41.1 kHz, and then intra-cavity pulse energy of a envelope reached about 609 nJ. This phenomenon was first observed in thulium-doped fiber laser. It will add experimental basis for studying of the pulse dynamics in fiber lasers.