Influence of amplified spontaneous emission on laser linewidth in a fiber amplifier

Spectral broadening due to amplified spontaneous emission (ASE) in a fiber amplifier is experimentally and theoretically investigated in this paper. By measuring and analyzing the variation in linewidth and noise of the fiber amplifier, the influence of ASE on laser linewidth is studied. The analysis shows that the ASE will cause broadening of the laser linewidth as noise, and the noise is introduced as an additive term rather than a multiplicative one.