Q-switched Dy:ZBLAN fiber lasers beyond 3 µm: comparison of pulse generation using acousto-optic modulation and inkjet-printed black phosphorus

We report high-energy mid-infrared pulse generation by Q-switching of dysprosium-doped fiber lasers for the first ti me. Two different modulation techniques are demonstrated. Firstly, using active acousto-optic modulation, pulses are produced with up to 12 µJ energy and durations as short as 270 ns, with variable repetition rates from 100 Hz to 20 kHz and central wavelengths tunable from 2.97 to 3.23 µm. Experiments are supported by numerical modeling, identifying routes for improved pulse energies and to avoid multi-pulsing by careful choice of modulator parameters. Secondly, we demonstrate passive Q-switching by fabricating an inkjet-printed black phosphorus saturable absorber, simplifying the cavity and generating 1.0 µJ pulses with 740 ns duration. The performance and relative merits of each modulation approach are then critically discussed. These demonstrations highlight the potential of dysprosium as a versatile gain medium for high-performance pulsed sources beyond 3 µm.