Effect of linewidth on intensity noise induced by stimulated Brillouin scattering in single-mode fibers.

Non-linear effects and intensity noise characteristics are critical factors that influence the performance of fiber communication systems as well as fiber-based sensors. It is observed in our experiment that relative intensity noise (RIN) subsequent to fiber transmission has a strong dependence on laser linewidth. Over a short transmission distance, RIN decreases with a narrowing laser linewidth. For longer distances, a narrower laser linewidth will result in a smaller RIN in a frequency range higher than 1 MHz and a larger RIN in a low-frequency range. In this study, the Brillouin linewidth parameter is introduced into a stimulated Brillouin scattering (SBS) three-wave coupling equation to simulate RIN variation phenomenon. Excellent agreement between the theoretical and experimental RIN spectra was obtained. We initially prove that the phenomenon is primarily owing to SBS. It is believed that the experimentally observed phenomena and theoretical justification presented in this study is significant in improving the performance of communication systems and fiber-based sensors.