Cladding-pumped Raman fiber amplifier

Cladding-pumped rare-earth-doped fibers and Raman fiber devices have been two of the most compelling advances in the area of high-power fiber amplifiers and lasers in recent years. Cladding-pumping enables pumping with multi-mode pump sources that deliver high-power at a low cost The core of the double-clad fiber can still be single-moded, so that single-mode amplification or lasing can be realized. Raman gain requires high pump powers and Raman conversion is therefore only efficient at high power levels. On the other band, Raman devices are very flexible as gain is available at arbitrary wavelengths with the right pump source. Cladding-pumped Raman fiber devices represent a natural progression to multi-mode pumping and Raman fiber devices. While cladding-pumped Raman fiber devices require pump powers of, say, 100 W, such powers are available from fiber sources as well as from traditional bulk sources. For example, a multimode Nd-doped fiber laser with 1 kW of output power was recently reported. With pulsed sources, however, the required peak powers can be achieved with relatively modest average powers. Here, we report for the first time Raman amplification in a cladding-pumped fiber, without any rare-earth doping. We believe that this is an important step towards a whole class of new optical amplifier devices based on brightness-enhancing nonlinear conversion of multimode pumps, including not only Raman converters but also Brillouin and optical parametric converters.