Self-Q-switched single-longitudinal-mode erbium-doped fiber laser

We propose a simple single-longitudinal-mode (SLM) self-Q-switched erbium-doped fiber laser, where both Q-switching and SLM operation rely on a 1.5-meter high-concentration erbium-doped photonic crystal fiber (ED-PCF), which provides saturable absorption and nonlinear effects. By adjusting the pump power, we achieved stable SLM Q-switched pulse output, with the repetition frequency ranging from 20 kHz to 120 kHz, the pulse width from 5 µs to 500 ns, and the SLM linewidth consistently less than 7.5 MHz.