Efficient Lasing Through Raman-Assisted Four-Wave Mixing With Intrinsic Weak Spectral Broadening Characteristics

Narrow linewidth nonlinear frequency conversion has attracted numerous research attentions. In this manuscript, we demonstrate efficient frequency conversion with weak spectral broadening characteristics through Raman-assisted four-wave mixing (FWM) process in birefringent phosphosilicate fiber. The output power of the generated Stokes light reaches 12.05 W, with a conversion efficiency of 67.4%. Compared to previously reported FWM-based fiber lasers with output power and conversion efficiency below watt level and 50% respectively, our result shows significant improvement. Besides, benefiting from the strict phase match requirement of FWM process, this laser system has unique advantages in suppressing spectral broadening, the output linewidth of which is less than half of the conventional Raman fiber laser under same power level. Furtherly, we propose a power balance model to describe the power evolution characteristics of the Raman-assisted FWM process, proving the advantage of phosphosilicate fiber in improving the conversion efficiency of FWM process. This work gives a reference for efficient narrow linewidth frequency conversion or amplification.