Ultra-narrow linewidth SOA fiber laser assisted by distributed self-injection feedbacks

In this work, we demonstrate an ultra-narrow linewidth SOA fiber laser with single-longitudinal-mode (SLM) operation, wherein the side mode is suppressed by the Rayleigh backscattering (RBS) in a distributed self-injection feedback structure (DSIFS). Herein, the high scattering fiber (HSF) with a large scattering coefficient is employed as the DSIFS to soar the amount of RBS signal. In this experiment, a hybrid laser is constructed by the HSF serving as the feedback medium of ring main cavity. The SLM operation and linewidth narrowing of the proposed laser at different pump currents under the premise of stable laser output are discussed. Our experimental results show that the side mode suppression ratio of the SOA fiber laser is 70 dB with an output linewidth is less than 540 Hz. The 50 m HSF is employed to achieve laser side mode suppression and deep compression of linewidth, which greatly simplifies the system and improves performance of the laser