Stationary High-Energy Pulse Generation in Er-Based Fiber Lasers via Quasi-Synchronous Gain Modulation

We demonstrate the feasibility of triggering stationary high-energy pulse generation in Er-doped fiber lasers at ~1.5 µm via quasi-synchronous gain modulation. This simple method relies upon the sine-wave modulation of pump power at a frequency slightly surpassing the intrinsic frequency spacing of longitudinal modes in the laser cavity. This was previously implemented only in Yb-doped fiber lasers at ~1.1 µm. Here, for the first time, we experimentally validate the pulse shaping capabilities of this method also in Er fiber lasers, which, unlike Yb fiber lasers, have a three-level laser energy diagram (when pumped at 0.98 µm) with a very long-lived (10 ms) upper laser level. The feasibility of the method was validated both for normal and anomalous intracavity dispersion, which was not available in previous implementations in Yb fiber lasers at ~1.1 µm. Thus, the stable generation of a regular train of discrete nanosecond pulses with an energy of up to 180 nJ was achieved in our test-bed Er fiber laser upon the quasi-synchronous sine-wave modulation of the pump power at 0.98 µm. The results of our study testify to the general applicability of this affordable and reliable method for high-energy pulse generation in various rare-earth-doped fiber lasers.