Generation of stable nanosecond dual-pulse in an erbium-doped fiber laser with normal dispersion

Because of the special needs for nanosecond double pulse applications in micromachining and material processing, we demonstrated a stable nanosecond dual-pulse erbium-doped fiber laser based on nonlinear polarization rotation technology. The fiber laser operates in a normal dispersion regime with a length of 256 m OFS-980 fiber. With the pump power of 1120 mW, the laser generates a highly stable dual-pulse train with the pulse widths of 6.2 ns and 1.2 ns respectively. By simply changing the pump power, the pulse width of one of dual-pulse can be tuned from 2.1 to 6.2 ns while the other pulse keeping almost the same duration of 1.2 ns. The maximum dual-pulse energy is about 72.5 nJ with a repetition rate of 783.3 kHz. The formation of such nanosecond dual-pulse is attributed to the pulse splitting and depends on the parameters of the laser cavity, such as the cavity-length and the state of polarization controller. The experiment of a single square pulse splitting into different shapes of nanosecond dual-pulse was demonstrated.