Random lasing with narrow linewidth in a short Er-doped fiber

Random lasing is directly generated in a short erbium-doped fiber (EDF) for the first time, pumped by a 980 nm highly stable laser source. We investigated the threshold and efficiency of the erbium-doped random fiber laser (ERFL) in dependence on the length of EDF. The ERFL has the lowest threshold power of 15.2 mW and the maximum optical conversion efficiency of 16% at the EDF of 11 m. We also explored output spectral characteristics of ERFL based on the EDF of 11 m. It is found that the spectral peaks vary randomly with the highest optical signal-noise ratio (OSNR) of 28.5 dB under the same pump power, and the linewidth narrows to 300 Hz. Moreover, random peaks undergo red shift over time and the number of random peaks is increased with the enhancement of pump power. Therefore, this work offers a chance in development of a simple and reliable method to realize ERFL with narrow linewidth.