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, we 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 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. We 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.
Zhang Hanwei, Zhou Pu, Xiao Hu, Leng Jinyong, Tao Rumao, Wang Xiaolin, Xu Jiangming, Xu Xiaojun, Liu Zejin. Towards High Power Nonlinear Fiber Amplifier[J]. High Power Laser Science and Engineering, , (): .
