Highly efficient first order Raman fibre lasers using very short Ge-doped silica fibres

We demonstrate first order Raman fibre lasers that use short lengths of low loss moderately (18 mol%) Ge-doped fibre. The Raman fibre lasers were pumped with a 14 W Yb³⁺-doped double clad fibre laser operating at a wavelength of 1106 nm. In a simple resonator configuration, the cavity of the Raman fibre lasers did not employ Bragg gratings and used a broadband dielectric mirror and ∼4% Fresnel reflection for feedback. The shortest fibre length of 10 m produced a first order Raman output of 5 W at slope efficiency of 82% and with the use of a 25 m length of fibre; a maximum first Stokes output power of 8 W was demonstrated at a slope efficiency of 76%. The use of short highly nonlinear Ge-doped fibres for Raman fibre lasers will be useful for a wide range of applications.