A Novel Structure for Raman Suppression in Narrow Linewidth Fiber Amplifier

In this letter, we proposed a novel structure for the suppression of stimulated Raman scattering (SRS) in high-power narrow linewidth fiber amplifier seeded by fiber Bragg grating -based oscillator. By introducing broadband external feedback into the laser cavity, an ultra-stable continuous-wave seed was acquired by suppressing the self-pulsations in the fiber oscillator. Accordingly, the SRS threshold of the amplifier was improved significantly. The advantages of this structure and its usability in narrow linewidth fiber lasers have been explained carefully. Based on this novel structure, a 3.5 kW single mode narrow linewidth fiber amplifier was obtained with high signal to Raman ratio of 40 dB. This work provides a simple and effective approach for SRS suppression in high-power narrow linewidth fiber amplifiers.