Q-switched mode locking noise-like pulse generation from a thulium-doped all-fiber laser based on nonlinear polarization rotation

Q-switched mode locking (QML) noise-like pulse (NLP) emission from an all-fiber thulium-doped laser based on the nonlinear polarization rotation effect is reported. The QML emission is obtained in a cavity with net anomalous dispersion in a pump power interval in between the CW laser threshold and the threshold of the NLP regime. Highest-energy QML pulses were observed with a repetition rate of 812 kHz with a pump power of 520 mW at the optical wavelength of 1881.09 nm. A maximum overall energy of 460 nJ at an average output power of 6.4 mW was reached, which corresponds to a burst of mode-locked noise-like sub-pulses with 8.7 ns of pulse duration within a QML envelope of 11 µs. These results demonstrate unconventional pulse operation regime of NLPs and provide insights into the dynamics of mode-locked fiber lasers.