HIGH-POWER FIBER LASERS: Doping management leads to better fiber-laser output

摘要

To create a short-pulse fiber laser with simultaneous high-average-power output and high peak powers presents a conundrum. Increasing average power requires minimizing thermal effects, which leads to longer gain fibers with lower doping; however, increasing peak power requires minimizing nonlinear effects, which leads to shorter fibers with higher levels of doping. Researchers at Bilkent University and FiberLAST Inc. (both in Ankara, Turkey) and TUBITAK Ulusal Metroloji Enstitusu (Kocaeli, Turkey) have created a forward-pumped short-pulse fiber laser in which the amount of dopant varies along the fiber. In analogy to dispersion management of fibers, the researchers call their technique "doping management." At the beginning of the fiber's last amplifier stage, where the amplifier output is lower and pump level is at its highest, the fiber has low doping to reduce thermal load. Further along, where output is greater and pump level is lower, the fiber is more heavily doped, minimizing gain length to reduce nonlinear effects. Because it is difficult to create a fiber in which doping level varies continuously, the researchers created a prototype with two differently doped segments (more can be used later).