[1] [1] Richardson D J, Nilsson J, Clarkson W A. High power fiber lasers: current status and future perspectives [Invited][J]. Journal of the Optical Society of America B, 2010, 27(11): B63-B92.

[2] [2] Zhou Pu. Study on Coherent Beam Combination Technology of Fiber Lasers[D]. Changsha: National University of Defense Technology, 2009.

[3] [3] Koponen J J, Sderlund M J, Hoffman H J, et al.. Measuring photodarkening from single-mode ytterbium doped silica fibers[J]. Opt Express, 2006, 14(24): 11539-11544.

[4] [4] Taccheo S, Taccheo S, Gebavi H, et al.. Concentration dependence and self-similarity of photodarkening losses induced in Yb-doped fibers by comparable excitation[J]. Opt Express, 2011, 19(20): 19340-19345.

[5] [5] NEWSLETTERLIFT#6. Application oriented research in the area of high-brillionge fiber lasers. http://www.lift-project.eu/pdf/lift_newsletter_6.pdf.[2013-12-12].

[6] [6] Zhu Zongjiu, Xu Lixin, Mao Qinghe, et al.. Photodarkening in ytterbium-doped fiber with high doping concentration[J]. Acta Photonica Sinica, 2007, 36(1): 26-29.

[7] [7] Hao J, Yan P, Gong M. Effect of mode competition on photodarkening distribution of Yb-doped fiber laser[J]. Opt Commun, 2013, 287: 167-175.

[8] [8] CHENG Y. Research on photodarkening in rare earth doped fibers[J]. Journal of Rare Earths, 2012, 30(11): 1102-1105.

[9] [9] Koponen J J, Sderlund M J, Tammela S K T, et al.. Photodarkening in ytterbium-doped silica fibers[C]. SPIE, 2005, 5990: 59908.

[10] [10] Olivero M, Braglia A, Perrone G, et al.. Improved setup and procedure for benchmarking of photodarkening in ytterbium doped silica fibers[J]. Journal of Optics, 2012, 14(12): 125702.

[11] [11] Koponen J, Laurila M, Hotoleanu M. Inversion behavior in core- and cladding-pumped Yb-doped fiber photodarkening measurements[J]. Appl Opt, 2008, 47(25): 4522-4528.

[12] [12] Jetschke S, Schwuchow A, Unger S, et al.. Deactivation of Yb3+ ions due to photodarkening[J]. Optical Materials Express, 2013, 3(4): 452-458.

[13] [13] Deschamps T, Vezin H, Gonnet C, et al.. Evidence of AlOHC responsible for the radiation-induced darkening in Yb doped fiber[J]. Opt Express, 2013, 21(7): 8382-8392.

[14] [14] Guzman Chávez A D, Kir′yanov A V, Barmenkov YuO, et al.. Reversible photo-darkening and resonant photobleaching of ytterbium-doped silica fiber at in-core 977 nm and 543 nm irradiation[J]. Laser Phys Lett, 2007, 4(10): 734-739.

[15] [15] Rydberg S, Engholm M. Experimental evidence for the formation of divalent ytterbium in the photodarkening process of Yb-doped fiber lasers[J]. Opt Express, 2013, 21(6): 6681-6688.

[16] [16] Gebavi H, Taccheo S, Tregoat D, et al.. Photobleaching of photodarkening in ytterbium doped aluminosilicate fibers with 633 nm irradiation[J]. Optical Materials Express, 2012, 2(9): 1286-1291.