Yang Baolai, Zhang Hanwei, Shi Chen, Wang Xiaolin, Pan Zhiyong, Wang Zefeng, Zhou Pu, Xu Xiaojun
Opt Express. 2019 Mar 4;27(5):7585-7592. doi: 10.1364/OE.27.007585.
In the power scaling of monolithic fiber lasers, the fiber nonlinear effects and transverse mode instability are main limitations. The tapered gain fiber has a longitudinally varying mode area, which has the advantage of mitigating fiber nonlinear effects. However, the transverse mode instability (TMI) was seldom reported in the tapered fiber lasers at high average power levels. In this work, we have constructed a monolithic tapered ytterbium-doped fiber laser oscillator and investigated the laser oscillator performance with respective 976 nm and 915 nm pump, especially on the aspects of the TMI. The double cladding tapered ytterbium-doped fiber has a narrow end of ~20/400 μm and a wide end of ~30/600 μm. Fiber Bragg gratings (FBG) are respectively inscribed on double cladding fibers with core/inner cladding diameter of 20/400 μm and 30/400 μm to match with the narrow and wide end of the tapered ytterbium-doped fiber. When 915 nm pump is employed, the TMI occurs at the output power of ~1350 W. The output power is further scaled to a maximum of 1720 W. The M factor of the output laser is ~2.1 and the full width at half maximum (FWHM) of the signal laser is ~3.6 nm. To the best of our knowledge, this is the highest average power for the tapered ytterbium-doped fiber lasers.
在单片光纤激光器的功率缩放中，光纤非线性效应和横向模式不稳定性是主要限制因素。锥形增益光纤具有纵向变化的模式面积，这有利于减轻光纤非线性效应。然而，在高平均功率水平下的锥形光纤激光器中，横向模式不稳定性（TMI）鲜有报道。在这项工作中，我们构建了一个单片锥形掺镱光纤激光振荡器，并分别用976 nm和915 nm泵浦研究了该激光振荡器的性能，特别是在TMI方面。双包层锥形掺镱光纤的窄端约为20/400μm，宽端约为30/600μm。光纤布拉格光栅（FBG）分别写入纤芯/内包层直径为20/400μm和30/400μm的双包层光纤中，以匹配锥形掺镱光纤的窄端和宽端。当采用915 nm泵浦时，TMI在输出功率约为1350 W时出现。输出功率进一步缩放至最大值1720 W。输出激光的M因子约为2.1，信号激光的半高全宽（FWHM）约为3.6 nm。据我们所知，这是锥形掺镱光纤激光器的最高平均功率。
