Side mode suppression of SOA fiber hybrid laser based on distributed self-injection feedback

Abstract An ultra-narrow linewidth semiconductor optical amplifier (SOA) fiber laser based on a novel configuration in which the main cavity is combined with a distributed external-cavity feedback is proposed and demonstrated. In this work, a high scattering fiber (HSF) is utilized as the weak feedback medium to suppress the side longitudinal mode of the SOA fiber hybrid laser. A model is established to theoretically reveal the side mode suppression effect of the distributed feedback. The experimental results demonstrate that the HSF effectively enhances the feedback intensity of the Rayleigh backscattered signal and successfully enhances the side mode suppression ratio (SMSR) of the main cavity to 58 dB. Likewise, the output linewidth is as low as 420 Hz. The laser frequency noise reaches ∼66.3 Hz2/Hz in the high frequency range, and the measured RIN is less than −130 dB/Hz at frequencies of over 0.5 MHz. This work presents an effective mechanism to regulate the longitudinal mode operation in highly coherent lasers.