Raman Amplification And Pulsed Lasing In Cladding-Pumped Germanosilicate Fiber

Introduction: Cladding-pumped rare-earth-doped fibers and Raman fiber devices have been two of the most compelling advances in the area of fiber amplifiers and lasers in recent years. Both cladding-pumped fibers and Raman fiber devices are primarily high-power devices. 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 robust single-mode amplification or lasing can be realized. Claddingpumped silica fiber lasers and amplifiers have been demonstrated at 980 nm [1, 2, 3] and 1020 – 1150 nm [4] with Yb-doping, 1050 – 1120 nm with Nd-doping [5], 1530 – 1620 nm with Er-doping (normally with, but also without, Yb co-doping) [6], and 2000 – 2200 nm with Tm-doping [7]. These rare earths can be pumped by widely available high-power diode sources at around 800 nm or 910 – 980 nm. Raman gain requires high pump powers. Raman fiber lasers are therefore only efficient at high power levels. On the other hand, Raman devices are very flexible in that gain is available at arbitrary wavelengths with the right pump source. Thus, a popular configuration for distributed Raman amplification at 1550 nm is to use a cascaded Raman laser as a pump source at 1450 nm (where rareearth doped lasers are not available), which is in turn pumped by a high-power cladding-pumped Ybdoped fiber laser at 1060 nm. Besides this example, cladding-pumped fiber devices have many other real and potential applications in telecom and other areas, such as high-power fiber amplifiers, and sources for remote sensing (e.g., lidar). Raman amplification can be used for distributed or lumped amplification in telecom systems, but also more generally as a means for wavelength conversion (notably in cascaded Raman lasers). Cladding-pumped Raman fiber devices, an exciting combination of multi-mode pumping and Raman amplification, have recently been proposed [8]. With such devices, single-mode gain can be created at arbitrary wavelengths with multi-mode pump sources (at the right wavelength). Conversely, any multimode source with sufficiently high power can be Raman-converted to a single-mode beam in a double-clad fiber configured as an amplifier or as a laser. One is no longer restricted to the absorption and emission bands of rare earths. While cladding-pumped Raman fiber devices require pump powers of, say, 100 W, such powers are available from fiber sources as well as traditional bulk sources. For