Rayleigh scattering assisted ultra-narrow linewidth linear-cavity laser

We demonstrate the evolution characteristics of laser linewidth in accordance to Rayleigh backscattering (RBS) signal accumulated from different lengths of the RBS fiber. An ultra-narrow-linewidth fiber laser operating in single longitudinal mode has been obtained. The output linewidth is approximately 210 Hz and the side-mode suppression ratio is as high as ∼60 dB provided the length of the RBS fiber is set to be 5 km. The theoretical prediction suggests linewidth of tens of Hertz could be achieved provided the experimental setup is further optimized and the temperature control device is introduced.