Experimental Study of the Nonlinear Dynamics of an Actively Q-Switched Ytterbium-Doped Fiber Laser

In this paper, a comprehensive experimental study of the dynamics of an actively Q-switched Yb-doped GTWave-based fiber laser is presented. It is shown that the appearance of the Q-switching regime in the laser is sensitive to both the repetition rate and the temporal width of the transparency window of an acousto-optical Q-switch modulator placed in the cavity. It is also shown that, at low repetition rates, a peculiar self-Q-switch regime induced by stimulated Brillouin scattering is observed in the laser, which interferes stochastically with the regular (true) active Q-switching mode. While increasing the Q-modulator repetition rate, the self-Q-switch pulsing steadily vanishes but the true Q-switching remains. The latter, however, becomes strongly subjected, while further increasing the Q-switch repetition rate, by the nonlinear laser dynamics effects. That is, the laser is allowed to operate at certain subharmonics of the repetition rate or in some specific regimes that occur at laser transients from one attractor to another. These transient regimes are characterized by alternating between pulse amplitude and energy, and pulse spacing or chaos, which is strongly influenced by the adjacent attractors' properties.