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模式不稳定发现于2010年，是影响高功率光纤激光器功率提升的重要限制因素.当前模式不稳定主要有两类，一类是动态模式不稳定，一类是准静态模式不稳定.本文研究了纤芯/内包层直径为25 μm/400 μm掺镱双包层光纤后向抽运放大器中的模式不稳定效应.通过对功率、光束质量和时域数据的分析，发现在该放大器中出现了准静态模式不稳定的现象，随着抽运功率的增加，放大器输出光束质量逐步退化，而时域上没有发现明显的动态模式不稳定特性.实验上对不同种子功率下放大器的输出特性进行研究，结果表明，通过提高种子激光功率可以较为有效地提高模式不稳定阈值，在种子功率为528 W时，当输出功率大于3000 W，输出激光效率没有明显下降.One of the most outstanding limitations in the evolution of the power scaling of fiber laser with near diffraction limited beam quality has been the mode instability since it was found in 2010. For a long time, researchers have focused on the dynamic mode instability (DMI) theoretically and experimentally, and it was not until 2016 that a new analytical model called quasi-static mode instability (QSMI) was proposed. Unlike DMI, because of the one-way energy transfer characteristic on a specific time scale, QSMI will show no apparent fluctuations with respect to the time domain traces. In this paper, based on a counter-pump few-mode fiber amplifier schematic system, the output power, beam quality and time traces of the amplifier under changing seed laser power are measured to investigate its mode instability effect. The ytterbium-doped fiber of the amplifier has a core diameter of 25 μm and inner cladding diameter of 400 μm, which can support 4-5 modes to be transmitted in the amplifier. The experimental results reveal that QSMI happens in the few-mode fiber amplifier. Taking 234 W seed power for example, it is found that when the output power reaches 2030 W, the optical-to-optical efficiency begins to fell from 86% to 32%, and at the same time the M2 value has an abrupt degradation from 2.2 to 2.8, which indicates that MI happens. On the other hand, it can be seen from the time traces of the output laser that there exist no rapid fluctuations, and the Fourier analysis shows no sign of DMI characteristic frequency components either. Quoting the definition of drifting ratio σ, when the output power is 2030 W under 234 W seed power, it is only 4%, and thus verifying that it is QSMI instead of DMI. The experiment also indicates that increasing the seed power has an effective influence on enhancing the mode instability power. When the seed power is raised from 86 W to 528 W, the corresponding threshold power is increased from 1560 W to 3090 W. And for 528 W seed power, when the output laser surpasses 3000 W, the optical-to-optical efficiency does not decline as fast as other relatively low seed power. To sum up, the mode instability effect represents a kind of quasi-static property in these large core diameter few-mode fiber amplifiers, which needs further studying.
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Keywords:
- few-mode fiber /
- mode instability /
- beam quality /
- quasi-static
[1] Limpert J 2017 Optical Fiber Communications Conference and Exhibition Los Angeles, March 13-19, 2017 p1
[2] Zervas M N 2017 European Conference on Lasers and Electro-Optics European Quantum Electronics Conference Munich, June 25-29, 2017 p1
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[22] Ward B 2016 Opt. Express 24 3488
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[25] Wang X L, Zhang H W, Tao R M, Su R T, Ma P F, Zhou P, Xu X J 2017 European Conference on Lasers and Electro-Optics European Quantum Electronics Conference Munich, June 25-29, 2017 CJ_6_3
[26] Otto H, Jauregui C, Stutzki F, Jansen F, Limpert J, Tnnermann A 2013 Advanced Solid-State Lasers Congress Paris, October 27-November 1, 2013 ATu3A.02
[27] Tao R M, Wang X L, Zhou P, Liu Z 2017 J. Opt. 19 065202
[28] Tao R M, Zhou P, Wang X L, Si L, Liu Z J 2014 Acta Phys. Sin. 63 085202 (in Chinese) [陶汝茂, 周朴, 王小林, 司磊, 刘泽金 2014 物理学报 63 085202]
[29] Tao R M, Ma P F, Wang X L, Zhou P, Liu Z J 2016 J. Opt. 18 65501
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[1] Limpert J 2017 Optical Fiber Communications Conference and Exhibition Los Angeles, March 13-19, 2017 p1
[2] Zervas M N 2017 European Conference on Lasers and Electro-Optics European Quantum Electronics Conference Munich, June 25-29, 2017 p1
[3] Otto H, Jauregui C, Limpert J, Tnnermann A 2015 SPIE 9728 1
[4] Eidam T, Hanf S, Seise E, Andersen T V, Gabler T, Wirth C, Schreiber T, Limpert J, Tnnermann A 2010 Opt. Lett. 35 94
[5] Khitrov V, Farley K, Majid I, Christensen S, Samson B 2010 SPIE 7686 78
[6] Ward B G 2015 Opt. Lett. 40 542
[7] Yu C X, Shatrovoy O, Fan T Y, Taunay T F 2016 Opt. Lett. 41 5202
[8] Otto H, Modsching N, Jauregui C, Limpert J, Tnnermann A 2015 Opt. Express 23 15265
[9] Eidam T, Wirth C, Jauregui C, Stutzki F, Jansen F, Otto H, Schmidt O, Schreiber T, Limpert J, Tnnermann A 2011 Opt. Express 19 13218
[10] Otto H, Stutzki F, Modsching N, Jauregui C, Limpert J, Tnnermann A 2014 Opt. Lett. 39 6446
[11] Brar K, Savage-Leuchs M, Henrie J, Courtney S, Dilley C, Afzal R, Honea E 2014 SPIE 896 1
[12] Yang B L, Zhang H W, Shi C, Wang X L, Zhou P, Xu X J, Chen J B, Liu Z J, Lu Q S 2016 Opt. Express 24 27828
[13] Laurila M, Jorgensen M M, L gsgaard J, Alkeskjold T T 2013 Conference on Lasers and Electro-Optics International Quantum Electronics Conference Munich, May 12-16, 2013 CJ_3_5
[14] Puju P V, Zelenova M Z, Tyrtyshnyy V A 2016 International Conference Laser Optics, St. Petersburg June 27-July 1, 2016 p1
[15] Wang X L, Tao R M, Xiao H, Zhou P, Zhang C D, Xu X J 2013 Advance Solid-State Laser Paris, October 27-November 1, 2013 JTh2A. 44
[16] Jauregui C, Eidam T, Otto H, Stutzki F, Jansen F, Limpert J, Tnnermann A 2012 Opt. Express 20 12912
[17] Jauregui C, Eidam T, Otto H, Stutzki F, Jansen F, Limpert J, Tnermann A 2012 Opt. Express 20 440
[18] Smith A V, Smith J J 2011 Opt. Express 19 10180
[19] Smith A V, Smith J J 2013 IEEE Photon. J. 5 7100807
[20] Ward B, Robin C, Dajani I 2012 Opt. Express 20 11407
[21] Dong L 2013 Opt. Express 21 2642
[22] Ward B 2016 Opt. Express 24 3488
[23] Lægsgaard J 2016 Opt. Express 24 13429
[24] Gebavi H, Taccheo S, Lablonde L, Cadier B, Robin T, Mechin D, Tregoat D 2013 Opt. Lett. 38 196
[25] Wang X L, Zhang H W, Tao R M, Su R T, Ma P F, Zhou P, Xu X J 2017 European Conference on Lasers and Electro-Optics European Quantum Electronics Conference Munich, June 25-29, 2017 CJ_6_3
[26] Otto H, Jauregui C, Stutzki F, Jansen F, Limpert J, Tnnermann A 2013 Advanced Solid-State Lasers Congress Paris, October 27-November 1, 2013 ATu3A.02
[27] Tao R M, Wang X L, Zhou P, Liu Z 2017 J. Opt. 19 065202
[28] Tao R M, Zhou P, Wang X L, Si L, Liu Z J 2014 Acta Phys. Sin. 63 085202 (in Chinese) [陶汝茂, 周朴, 王小林, 司磊, 刘泽金 2014 物理学报 63 085202]
[29] Tao R M, Ma P F, Wang X L, Zhou P, Liu Z J 2016 J. Opt. 18 65501
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