Experimental investigation on amplification and coherence properties of a single-frequency and dual-single-frequency narrow-linewidth fiber Raman amplifier employing a switchable narrow-linewidth seed laser

We demonstrate a narrow-linewidth fiber Raman amplifier (NL-FRA) operating at single-frequency (SF) and dual-single-frequency (DSF) to study the amplification and coherence properties. A switchable NL seed laser at a central wavelength of 1079.7 nm is utilized to provide SF and DSF signal light for FRA. The signal light is Raman amplified to 791 mW and 1.07 W, respectively. Measurements of spectrum and frequency spectrum indicate that there is no significant indication of stimulated Brillouin scattering (SBS) and four-wave mixing (FWM). The experimental investigation on coherence properties of SF and DSF NL-FRA indicates that the optical-path-difference-control and control-servomechanism-system for coherent beam combination (CBC) of DSF NL-FRAs are more strictly required, but still feasible