Impact of Spectral Filter on Phase Modulation Pulse in Fiber Front End System

The transmission characteristics of phase modulation pulse transmitted through the filter in the power amplifier are investigated theoretically and experimentally. The narrow bandpass filter can induce large temporal modulation depth for the phase modulation pulse and induce double amplitude modulation (AM) if the frequency shift is lower than half bandwidth of the signal spectrum. We should choose a wider bandwidth filter to minimize the impact of the filter on the output pulse and suppress the amplified spontaneous emission (ASE) for the power fiber amplifier. These results are of benefit to the design of the fiber front end system.