Abstract
Stimulated Raman scattering (SRS) effect is considered to be one of the main obstacles for power scaling in general-type fiber lasers. Different from previous techniques that aim at suppressing SRS, nonlinear fiber amplifier (NFA), which manipulates and employs the SRS for power scaling in rare-earth-doped fiber, is under intensive research in recent years. In this paper, the authors will present an all-round study on this new kind of high-power fiber amplifier. A theoretical model is proposed based on the rate equation and amplified spontaneous emission (ASE), with random noise taken into account. By numerical solving of the theoretical model, the power scaling potential, heat analysis and advantages in suppressing the undesired backscattering light are quantificationally analyzed for the first time. Then two different types of high-power NFAs are demonstrated individually. Firstly, a laser diode pumped NFA has reached kilowatt output power, and the results agree well with theoretical predictions. Secondly, a tandem-pumped NFA is proposed for the first time and validated experimentally, in which 1.5 kW output power has been achieved. The authors also briefly discuss several new issues relating to the complex nonlinear dynamics that occur in high-power NFAs, which might be interesting topics for future endeavors.
Highlights
The output power of single chain fiber laser has been growing in recent years due to the fast development of pump laser diode (LD), active fiber, advanced heat management method, and so on
We focus on nonlinear fiber amplifier (NFA) based on Yb-doped fiber in this paper
In practical high-power NFA seeded by multi-wavelength laser, four wave mixing (FWM) might happen because the phase-mismatch could be compensated by the Yb gain[59]
Summary
The output power of single chain fiber laser has been growing in recent years due to the fast development of pump laser diode (LD), active fiber, advanced heat management method, and so on. Several independent groups have proposed a novel system setup[33,34,35,36,37,38,39,40] named Yb-Raman fiber amplifier or nonlinear fiber amplifier (NFA, we call it nonlinear fiber amplifier in this paper), where laser gain provided by both SRS and active fiber is employed. In this new setup, the signal laser is firstly amplified via doped ions in the fiber and the laser power is transferred into Stokes wave via SRS effect.
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