Comparison of asymmetric and symmetric cavity configurations of erbium-doped fiber laser in active Q-switched regime

We present a comparative analysis of the dynamics of an actively Q-switched erbium-doped fiber laser assembled in two configurations of Fabry-Perot cavity, asymmetric and symmetric, specified by the location of an acoustooptic Q-switch modulator relative to the output couplers. In both configurations, the length of an active (Er3+-doped) fiber is chosen such that the laser does not spuriously emit at the moments when the modulator is blocked, which is important for the pulse-on-demand operation. We show experimentally that the symmetric cavity configuration permits enlarging of the active fiber length twice as compared to the asymmetric one, thereby increasing the energy and decreasing the duration of output pulses. We also demonstrate that in the symmetric cavity configuration the laser emits a train of short (approximate to 18 ns width on a 3 dB level) and stable Q-switch pulses with a couple of much smaller in magnitude adjacent subpulses. We apply the traveling waves' method for making an accurate modeling of the laser dynamics in both implementations. The modeling takes into account all the point intracavity losses as well as the distributed ones, including the loss stemming from the excited-state absorption of Er3+ ions. The results of numerical simulations of the laser dynamics in both implementations are shown to be in excellent agreement with experiments. (c) 2012 Optical Society of America