Linearly polarized random fiber laser with ultimate efficiency

Linearly polarized pumping of a random fiber laser made of a 500-m PM fiber with PM fiber-loop mirror at one fiber end results in generation of linearly polarized radiation at 1.11 μm with the polarization extinction ratio as high as 25 dB at the output power of up to 9.4 W. The absolute optical efficiency of pump-to-Stokes wave conversion reaches 87%, which is close to the quantum limit and sets a record for Raman fiber lasers with random distributed feedback and with a linear cavity as well. Herewith, the output linewidth at high powers tends to saturation at a level of 1.8 nm.