Emerging applications, such as gravitational wave astronomy, demand single-frequency lasers with diffraction-limited emission at 1.5 μm. Fiber amplifiers have greatly evolved to fulfill these requirements. Hundreds of watts are feasible using large-mode-area and specialty fibers. However, their application in a few watts to tens of watts in monolithic systems is unnecessarily complex due to the poor commercial availability of fiber components and standard integration procedures. In this Letter we propose and experimentally demonstrate a novel and simple method to amplify single-frequency signals at 1.5 μm up to tens of watts by core-pumping single-mode ${\mathrm{Er}}^{3+}\text{:}{\mathrm{Yb}}^{3+}$ fiber amplifiers at 1018 nm. The proof-of-principle system is tested with different active fibers, lengths, and seed power levels. Over 11 W with an efficiency of more than 48% versus launched power is achieved. Additionally, performance degradation during operation was observed for which photodarkening due to P1 defects might be an explanation.

中文翻译：

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1556 nm的全光纤，单频率和单模Er ³⁺：Yb ³⁺光纤放大器； 1018 nm的泵浦光纤

诸如重力波天文学之类的新兴应用要求单频激光器的衍射极限发射为1.5μm。光纤放大器已经发展到可以满足这些要求。使用大模面积和特种光纤，数百瓦是可行的。但是，由于光纤组件的商业可用性差和标准的集成程序，它们在单片系统中的几瓦到几十瓦的应用不必要地复杂。在这封信中，我们提出并通过实验证明了一种新颖而简单的方法，即通过核心泵浦单模将1.5μm的单频信号放大到数十瓦特${尔}^{3+}\text{：}{b}^{3+}$1018 nm的光纤放大器。原理验证系统使用不同的有源光纤，长度和种子功率级别进行了测试。与发射功率相比，实现了超过11 W的效率，超过48％。此外，观察到操作期间的性能下降，这可能是由于P1缺陷引起的光暗化的原因。