Realization of femtosecond harmonic pulse and high-energy pulse envelope in a self-pulsing fiber laser

We report a self-pulsing Er-doped fiber laser (EDFL) which can respectively operate in different dynamic mode-locking regimes, including stable fundamental mode-locking (FML), bunched soliton mode-locking (BSML), harmonic mode-locking (HML) and Q-switched mode-locking (QML). The dynamic evolution of FML pulse to BSML pulse and finally to HML pulse shows a directly dependence on pumping power. At the pumping power of 29 mW, the fiber laser delivers the FML pulses with a repetition frequency of 11.64 MHz and pulse duration of 1.09 ps. The further increase of pumping power makes the FML pulse evolves into the BSML pulses with up to 9 sub-pulses. Once the pumping power reaches 210 mW, the 9th-order HML pulse with a pulse duration of 883 fs is realized. Moreover, the HML pulse can go into the QML regime by adjusting the intracavity polarization state, and the energy of pulse envelope reaches up to 344 nJ at the pumping power of 483 mW. To our best of knowledge, this is the first realization of BSML pulse, femtosecond HML pulse and >300 nJ pulse envelope in a self-pulsing EDFL.