Fiber oscillator of 5 kW using fiber Bragg gratings inscribed by a visible femtosecond laser
Hongye Li, Xin Tian, Hao Li, Baiyi Wu, Xiaofan Zhao, Meng Wang, Chenhui Gao, Binyu Rao, Xiaoming Xi, Zilun Chen, Zefeng Wang, Jinbao Chen
Abstract
We fabricate a pair of fiber Bragg gratings (FBGs) by a visible femtosecond laser phase mask scanning technique on passive large-mode-area double-cladding fibers for multi-kilowatt fiber oscillators. The bandwidth of high-reflection (HR) and lowreflection (LR) FBG is 1.6 nm and 0.3 nm, respectively. The reflection of the HR-FBG is higher than 99%, and that of the LR-FBG is about 10%. A bidirectional pumped all-fiber oscillator is constructed using this pair of FBGs, a record output power of 5027 W located in the signal core is achieved with a slope efficiency of 82.1%, and the beam quality factor M 2 is measured to be 1.6 at the maximum power. The FBGs are simply fixed on a water cooling plate without a special package, and the thermal efficiency of the HR-FBG and the LR-FBG is 2.76C/kW and 1C/kW, respectively. Our research provides an effective solution for robust high-power all-fiber laser oscillators.