Effective suppression of stimulated Raman scattering in high-power fiber oscillators using single CTFBG

We report the effective suppression of stimulated Raman scattering (SRS) in a high-power fiber laser oscillator with 15 m long delivery fibers by the insertion of a single chirped and tilted fiber Bragg grating (CTFBG). Inscribed in 20/400 μm fiber, the single CTFBG has been carefully designed and fabricated with a filter bandwidth of 22.8 nm to match the Raman gain spectrum. A maximum suppression ratio over 30 dB is achieved when the oscillator operates at 2.7 kW, with beam quality factor M2 of ~1.4. Moreover, the signal insertion loss is measured to be around 0.2 dB and the maximum temperature is about 41.6 °C at a room temperature of 25 °C. By improving the performance of CTFBG, a further power scaling and longer delivery distance of high-power fiber lasers could be achieved.