Pulsed Regimes of Erbium-Doped Fiber Laser Q-Switched Using Acousto-Optical Modulator

In this paper, we explore in details the operation regimes of an actively Q-switched erbium-doped fiber laser using a commercial acousto-optical modulator (AOM) and demonstrate that these regimes essentially depend on whether or not continuous-wave (CW) narrow-line lasing develops in the intervals when AOM is blocked. If such spurious CW lasing exists it always starts up within auxiliary low-Q cavity formed by an output coupler and weak reflections from AOM while the area where it occurs is limited by certain values of an active fiber's length and AOM's repetition rate. In the absence of spurious CW lasing (when shorter active fibers are used), the laser operates in the regime of “common” Q-switching where the shape of pulses can be easily managed by a proper waveform of the signal controlling the AOM's driver; pulse jittering in this regime is vastly negligible. In turn, when spurious CW lasing arises within the intervals when AOM is closed (this occurs at longer active fibers and at not too high AOM's repetition rates), the laser operates in the regime of SBS-induced pulsing where short and powerful pulses are released; pulse jittering in this case is perceptible and depends on AOM's repetition rate.