Integrated ytterbium-Raman fiber amplifier.

An integrated ytterbium-Raman fiber amplifier architecture is proposed for power scaling of a Raman fiber laser. It is an ytterbium (Yb) fiber amplifier seeded with a double or multiple wavelength laser and followed by a passive Raman fiber. The bluest wavelength light gets amplified in the Yb fiber and the power is transferred to redder wavelengths in the following Raman fiber. A proof of principle experiment demonstrates a 300 W all-fiber linearly polarized single mode amplifier at 1120 nm with an optical efficiency of 70%, limited only by available pump power. The amplifier consists of 4 m of Yb-doped fiber and 20 m of germanium-doped fiber, and seeded with a laser emitting at 1070 and 1120 nm. The power evolution of the 1070 and 1120 nm light inside the amplifier is investigated, both numerically and experimentally. The possibility of power scaling to over kilowatt levels is discussed.