Experimental study of backscattering pulses and broadband generation in a Q-switched MOPA

In a master oscillator fiber amplifier (MOPA) system, we have experimentally studied nonlinear phenomena originating in the amplifier Yb-fiber during amplification of Q-switched pulse. During amplification, the Yb-doped active fiber generated backscattered pulses followed by amplified pulse breaking and high peak power short pulse generation. The backscattered pulses were delayed maximum by 30ns and seed pulse of width 108ns was broadened to 140ns at 20KHz repetition rate due to different scattering effects in a 8m long Yb-doped double clad fiber. At higher pump power, the output pulse showed unstable pulse envelops and eventually broke into multiple short pulses. A broadband output was observed from 1050 to 1650nm. This unwanted pulse breaking was observed which caused catastrophic damage to the MOPA system occasionally.