Passive Q-switched mode-locked self-sweeping fiber laser

This Letter presents the first-ever, to the best of our knowledge, demonstration of a passive Q-switched mode-locked (QML) laser with wavelength self-sweeping. QML generation was observed in a figure-of-nine cavity Yb-doped fiber laser. A train of microsecond-long pulses was generated with each pulse consisting of a sequence of nanosecond-long pulses. The duration of the nanosecond-scale pulses was measured to be 3 ns, corresponding to the generation of ∼60 phase-locked longitudinal modes. At the same time, the spectral dynamics was self-induced wavelength sweeping with a sweeping range of up to 5 nm near 1075 nm. The results widen the understanding of the self-sweeping phenomenon and can be useful in applications requiring tunable pulsed radiation.