First Demonstration of Co-Pumped Single- Frequency Raman Fiber Amplifier With Spectral-Broadening-Free Property Enabled by Ultra-Low Noise Pumping

Single-frequency Raman fiber amplifier (RFA) has great potential applications in many regimes. Traditionally, counter-pumped manner is widely employed for its spectral linewidth broadening suppressing and maintaining single frequency property. In this paper, we propose the first demonstration of a co-pumped single-frequency RFA without linewidth broadening by applying the fiber laser with stable intensity as the pump source. The pump source with stable intensity is generated by cascaded power amplifying of a low noise, phase-modulated single-frequency seed laser. In this case, experimental results show that single frequency property of the RFA could be effectively maintained in the co-pumped manner. The contrast experiment is given with a conventional multi-longitudinal mode fiber oscillator as a pump source, and the linewidth is gradually broadened along with power scaling.