High-power 1.48 mu m phosphoro-silicate-fiber-based laser pumped by laser diodes

An all-fiber 1.48 mu m generator based on a LD-pumped Yb-doped double-cladl aser and cascaded Raman wavelength converter has been developed. Second-ord erRaman Stokes radiation was generated in a phosphosilicate-fiber resonator formed by two pairs of Bragg gratings. The Yb-doped double-clad fiber laser was pumped by seven laser diodes combined via a low-loss fused fiber coupl er and provided 4.4 W at 1.06 mu m at the input of the Raman converter. A s lope efficiency of the Raman converter of 40% with respect to the power emi tted by the double-clad Yb laser has been achieved. We obtained an output p ower of 1.5 W with a total optical-to-optical efficiency of 21%. It was fou nd that four-wave mixing, initiated in the fiber by the high-intensity ligh t, results in spectral broadening of the 1.48 mu m radiation and leaking of the first-Stokes radiation from the resonator formed by the 1.24 mu m Brag g gratings, thus reducing the efficiency of the first-to-second-Stokes conv ersion.