Generation of pulse bundles in a self-mode-locked Tm-doped double-clad fiber laser

In this paper, an all fiber self-mode-locked Tm-doped double-clad fiber ring laser is experimentally demonstrated. By inserting a piece of ∼95 m SMF-28 into the cavity to enhance the nonlinearity and bring in a large net anomalous dispersion, stable self-mode-locked operation with mode-locked pulse bundles has been observed. About ∼8 sub-pulses with unequal amplitude and identical separation are contained in each produced pulse bundle. The width and adjacent separation of each sub-pulse are about ∼1 ns and ∼63 ns, respectively. With increasing the pump power to ∼2.17 W, the maximum output power of ∼121 mW is achieved at central wavelength of ∼1962.6 nm.