High-power 1.48 (mo)m phosphoro-silicate-fiber-based laser pumped by laser diodes

An all-fiber 1.48 (mo)m generator based on a LD-pumped Yb-doped double-clad laser and cascaded Raman wavelength converter has been developed. Second-order Raman 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 coupler and provided 4.4 W at 1.06 (mo)m at the input of the Raman converter. A slope efficiency of the Raman converter of 40% with respect to the power emitted by the double-clad Yb laser has been achieved. We obtained an output power of 1.5 W with a total optical-to-optical efficiency of 21%. It was found that four-wave mixing, initiated in the fiber by the high-intensity light, results in spectral broadening of the 1.48 (mo)m radiation and leaking of the first-Stokes radiation from the resonator formed by the 1.24 (mo)m Bragg gratings, thus reducing the efficiency of the first-to-second-Stokes conversion.