Q-switched mode-locking noise-like rectangular pulses erbium-doped fiber laser

The Q-switched mode-locking(QML) rectangular pulses in the L-band erbium-doped passively mode-locked fiber laser based on nonlinear polarization rotation technique was researched experimentally. The Q-switched envelope of this type of pulses contained the rectangular pulse with fundamental repetition rate,which was confirmed as noise-like pulse by an autocorrelator. A 250 m long section of single mode fiber was inserted into the cavity to ensure the noise-like rectangular pulses easy to be obtained. By carefully adjusting polarization controllers and pump power in the cavity, both the continuous-wave mode-locking noise-like rectangular pulses with fundamental repetition rate of 778.21 kHz and the QML noise-like rectangular pulses with tunable repetition rate from 3.81 kHz to 9.01 kHz and the highest energy of Q-switched pulse envelop 1.06 J were achieved. The research results further reveal the fundamental physics of noise-like pulses and QML operation in the passively mode-locked fiber lasers.