Linewidth suppression mechanism of self-injection locked single-frequency fiber laser

Linewidth suppression mechanism of the self-injection locked single-frequency fiber laser (SFFL) is investigated theoretically and experimentally. An analytical model based on the semi-phenomenological approach is built up to characterize the optical feedback in SFFL. According to the theoretical prediction, the linewidth tends to be reduced with longer external cavity photon lifetime. Experimentally, a 200-Hz linewidth self-injection locked SFFL is achieved with 101 m long delay fiber, which agrees well with the theoretical simulation. The model provides a new perspective to understand the mechanism of linewidth reduction of self-injection locked SFFL.