摘要

基于自主研制的双锥形掺镱双包层光纤,开展了全光纤高功率光纤激光放大实验。激光系统实现了中心波长为1080nm、最高功率为4 kW的单模激光输出,其光光效率和斜率效率分别为82%和83%,质量因子(M2)为1.33,拉曼抑制比为44dB。实验结果表明,双锥形光纤具有同时提高非线性效应和模式不稳定性效应阈值的优势,有利于进一步提升高光束质量光纤激光器的输出功率。

Abstract

Objective In recent years, there has been a rapid progress in the development of high-power fiber lasers, which are widely used in the fields of laser marking and material processing as well as numerous industrial applications. The main factors that limit the output power of fiber lasers are the mode instability and nonlinear effects, including stimulated Raman scattering and stimulated Brillouin scattering. To suppress these nonlinearities, the core size of large mode area active fibers should be increased. However, this may lead to the degradation of beam quality. The core diameter of tapered fibers gradually increases as the length increases, therefore suppressing the nonlinear effects. Moreover, the tapered area, which satisfies the adiabatic taper principle, facilitates in achieving excellent beam quality. Tapered active fibers have been used in various applications such as continuous-wave fiber laser oscillators or amplifiers, ultrafast laser systems, and single-frequency fiber amplifiers. In early 2020, researchers from National University of Defense Technology proposed the Yb-doped double-tapered double-cladding fiber (DT-DCF), which consists of a thin-core section at both ends and a large-core section in the middle. In the present study, all-fiber high-power laser amplification is performed based on the self-fabricated Yb-doped DT-DCF. The laser system achieves a single-mode laser output with a maximum power of 4 kW and a mass factor M² of 1.33.

Methods We construct a master oscillator power amplifier system based on the homemade DT-DCF. This system is 21-m long and has small-core and large-core sections with core/cladding diameters of 22/413 and 32/600mm, respectively. Fusion splices connect all the components. The seed has a center wavelength of 1080 nm and a output power of 103 W. After passing through the cladding light striper (CLS), the seed light is injected into the amplifier. Subsequently, bidirectional pumping is applied to laser amplification. Seven laser diode (LD) modules with a center wavelength of 976 nm are divided into two groups comprising two and five modules to pump the DT-DCF through the forward and backward couplers, respectively. After the amplification stage, the CLS is utilized to strip out the residual pump power and the laser is finally output to free space through the endcap for the measurement of power, spectrum, and beam quality.

Results and Discussion The output power increases linearly with the pumping power. When the pumping power is 4.75kW, the output power reaches 4kW. The corresponding optical efficiency and slope efficiency are 82% and 83%, respectively. The M² at the highest power is 1.33 [Fig. 3(a)], exhibiting the single-mode output characteristic of the system. Mode instability limits further power scaling of the single-mode output. If the pump power increases to over 4.75kW, time domain fluctuation of kHz can be observed, indicating the initiation of mode instability. The output laser has a center wavelength of 1080nm, and its spectrum broadens as the output power increases. For the spectrum under the highest output power, the Raman suppression ratio reaches up to 44dB [Fig. 3(b)], demonstrating the ability of the DT-DCF to inhibit the nonlinear effects.

Conclusions In summary, we have established a 1080-nm all-fiber amplifier based on DT-DCF. This amplifier can achieve a 4-kW single-mode output laser with a slope efficiency of 83% and M² of 1.33. Our results indicate that the DT-DCF can simultaneously suppress the nonlinear effects and transverse mode instability, thus providing a beneficial reference for further power scaling of single-mode fiber lasers.

补充资料

中图分类号：TN248

DOI：10.3788/CJL202148.0115002

所属栏目：快报

基金项目：湖南创新型省份建设专项（2019RS3018）、湖南省自然科学基金创新研究群体项目（2019JJ10005）

收稿日期：2020-09-10

修改稿日期：2020-10-10

网络出版日期：2021-01-01

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联系人作者：黄良金(hlj203@nudt.edu.cn); 潘志勇(hlj203@nudt.edu.cn);

【1】Li X W, Yu C L, Hu L L, et al. 2.2 kW narrow-linewidth single-mode laser output using homemade 25/400 μm Yb-doped double cladding fiber [J]. Acta Optica Sinica. 2019, 39(6): 0636001.
李学文, 于春雷, 胡丽丽, 等. 国产25/400μm掺镱双包层光纤实现2.2 kW窄线宽单模激光输出 [J]. 光学学报. 2019, 39(6): 0636001.

【2】Yang B L, Wang X L, Ye Y, et al. All-fiber laser oscillator with 6 kW output power [J]. Chinese Journal of Lasers. 2020, 47(1): 0116001.
杨保来, 王小林, 叶云, 等. 全光纤激光振荡器输出功率突破6 kW [J]. 中国激光. 2020, 47(1): 0116001.

【3】Luo Y, Zhao P F, You Y F, et al. 5.1 kW single-mode fiber laser with integrated photoelectric control [J]. Chinese Journal of Lasers. 2020, 47(8): 0816001.
罗韵, 赵鹏飞, 游云峰, 等. 5.1 kW光电控一体式单模光纤激光器 [J]. 中国激光. 2020, 47(8): 0816001.

【4】Wang X L, Tao R M, Yang B L, et al. Relationship between transverse mode instability and stimulated Raman scattering in ytterbium doped all-fiber laser oscillator [J]. Chinese Journal of Lasers. 2018, 45(8): 0801008.
王小林, 陶汝茂, 杨保来, 等. 掺镱全光纤激光振荡器横向模式不稳定与受激拉曼散射的关系 [J]. 中国激光. 2018, 45(8): 0801008.

【5】Kerttula J, Filippov V, Ustimchik V, et al. Mode evolution in long tapered fibers with high tapering ratio [J]. Optics Express. 2012, 20(23): 25461-25470.Kerttula J, Filippov V, Ustimchik V, et al. Mode evolution in long tapered fibers with high tapering ratio [J]. Optics Express. 2012, 20(23): 25461-25470.

【6】Filippov V, Chamorovskii Y, Kerttula J, et al. Double clad tapered fiber for high power applications [J]. Optics Express. 2008, 16(3): 1929-1944.

【7】Filippov V, Kerttula J, Chamorovskii Y, et al. Highly efficient 750 W tapered double-clad ytterbium fiber laser [J]. Optics Express. 2010, 18(12): 12499-12512.

【8】Kerttula J, Filippov V, Chamorovskii Y, et al. Tapered fiber amplifier with high gain and output power [J]. Laser Physics. 2012, 22(11): 1734-1738.

【9】Trikshev A I, Kurkov A S, Tsvetkov V B, et al. A 160 W single-frequency laser based on an active tapered double-clad fiber amplifier [J]. Laser Physics Letters. 2013, 10(6): 065101.Trikshev A I, Kurkov A S, Tsvetkov V B, et al. A 160 W single-frequency laser based on an active tapered double-clad fiber amplifier [J]. Laser Physics Letters. 2013, 10(6): 065101.

【10】Zhou Z, Zhang H, Wang X, et al. All-fiber-integrated single frequency tapered fiber amplifier with near diffraction limited output [J]. Journal of Optics. 2016, 18(6): 065504.

【11】Lai W C, Ma P F, Liu W, et al. 550-W single-frequency all-fiber amplifier with near-diffraction-limited beam quality [J]. Chinese Journal of Lasers. 2020, 47(4): 0415001.
来文昌, 马鹏飞, 刘伟, 等. 全光纤单频光纤放大器实现550 W近衍射极限输出 [J]. 中国激光. 2020, 47(4): 0415001.

【12】Kerttula J, Filippov V, Chamorovskii Y, et al. Actively Q-switched 1.6-mJ tapered double-clad ytterbium-doped fiber laser [J]. Optics Express. 2010, 18(18): 18543-18549.

【13】Kim A. Fibre amplifier based on an ytterbium-doped active tapered fibre for the generation of megawatt peak power ultrashort optical pulses [J]. Quantum Electronics. 2015, 45(5): 443-450.

【14】Filippov V, Chamorovskii Y K, Golant K M, et al. Optical amplifiers and lasers based on tapered fiber geometry for power and energy scaling with low signal distortion [J]. Proceedings of SPIE. 2016, 9728: 97280V.

【15】Bobkov K K, Koptev M Y, Levchenk A E, et al. MW peak power diffraction limited monolithic Yb-doped tapered fiber amplifier [2020-09-10].https://www.zhangqiaokeyan.com/academic-conference-foreign_fiber-lasers-xiv-technology-systems_thesis/020512303926.html.[2020-09-10]. 0.

【16】Zeng L F, Xi X M, Ye Y, et al. A 1.8 kW fiber laser oscillator employing a section of spindle-shaped core ytterbium-doped fiber [J]. Laser Physics Letters. 2020, 17(9): 095104.

引用该论文

An Yi,Yang Huan,Xiao Hu,Chen Xiao,Huang Liangjin,Pan Zhiyong,Wang Xiaolin,Xi Xiaoming,Ma Pengfei,Wang Zefeng,Zhou Pu,Xu Xiaojun,Jiang Zongfu,Chen Jinbao. 4-kW Single-Mode Laser Output Using Homemade Double-Tapered Fiber[J]. Chinese Journal of Lasers, 2021, 48(1): 0115002

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