Theoretical Analysis of Thermal Distribution and Waveform Evolution in Pulsed Ytterbium-Doped Fiber Amplifier with Extra Feedback

Pulsed ytterbium-doped fiber amplifiers (YDFA) with ns-level signal width are important devices for obtaining high-power pulsed lasers. When some components in the amplifier are ineffective, e.g., the isolator or fiber is damaged, extra feedback light is generated and coupled into the gain fiber. The dynamic thermal distribution and waveform evolution of amplifiers with extra continuous-wave (CW) or pulse-wave (PW) feedback are theoretically analyzed in this work. The CW feedback can not only reduce the gain of the amplifier but can also change the thermal distribution of the gain fiber, while the PW feedback can reduce the leading or trailing edge of the output pulse by 3-4 ns, depending on the direction of the feedback light transmission. The theoretical analysis provides a reference for optimizing the thermal management and the fault diagnosis of a typical fiber amplifier with an output of several tens of watts.