Self-Q-switched and mode-locked erbium-ytterbium co-doped fiber laser

We demonstrated a self-Q-switched mode-locked erbium-ytterbium co-doped fiber laser at 1570 nm. The repetition rate of Q-switched pulses increased from 3.25 kHz to 24.41 kHz, whereas pulse width reduced from 28.8 µs to 4.61 µs. Self-mode-locked pulses appeared inside Q-switched pulses just above the threshold and transitioned into mode-locked pulses beyond a pump power of 695 mW. The average output power, minimum pulse duration, and repetition rate of the mode-locked pulses were 160 mW, 340 ps, and 6.57 MHz, respectively, at a pump power of 2.4 W. Self Q-switched pulses were obtained at low pump power ranging from 205 mW to 694 mW. At high pump power, the Q-switched mode-locked pulses were switched entirely to a mode-locked regime. They stayed up to the maximum available pump power of 2.4 W. We presented the characteristics of the mode-locked laser and discussed their origin.