-
光束质量和传输效率是光纤功率合束器最关键的两大性能指标,为最大限度降低光纤的功率损耗以及光束质量退化,合束器在制作中必须满足两大基本原则:绝热拉锥和亮度守恒。
-
光纤的拉锥过程改变了光纤的波导结构,锥区会不可避免地引入损耗,因此为了使损耗尽可能地小,锥区必须满足绝热拉锥条件[12]。通常认为,光纤锥区的长度越长,光纤波导结构的变化就越平缓,拉锥引起的损耗就越小。但拉锥长度过长,将会不利于后期的切割、熔接与封装。因此必须合理设计锥区长度,使其既满足绝热拉锥又方便实际操作。
-
亮度守恒原则可以计算出输入光纤的入射光能否全部被输出光纤接收。定义亮度比率(Brightness Ratio, BR)为合束器输出光纤的亮度与输入光纤的总亮度之比,
$$ BR = \frac{{D_{out}^2NA_{out}^2}}{{nD_{in}^2NA_{in}^2}} $$ 式中:
${D_{in}}$ 与${D_{out}}$ 分别为输出光纤与输入光纤的直径;$N{A_{in}}$ 与$N{A_{out}}$ 分别为输出光纤与输入光纤的数值孔径;n为输入光纤的数量;当亮度比率BR≥1时,${D_{out}^2NA_{out}^2}$ ≥${nD_{in}^2NA_{in}^2}$ ,即输出光的亮度大于输入光的总亮度,此时能保证合束器理论上可无损耗传输[13]。 -
在影响功率合束器光束质量的诸多因素中,其中一个重要因素就是熔融拉锥光纤束(Taper-Fused Fiber Bundles, TFB)的纤芯占空比。TFB的纤芯占空比可以理解为拉锥后玻璃管内光纤的纤芯直径与相邻两光纤之间的距离之比,而增大TFB的纤芯占空比理论上可以提高功率合束器的光束质量。增大占空比即需使输入光纤的包层尽可能地薄,因为文中研制合束器所用激光器的输出光纤是25/400 μm光纤,如果直接作为输入光纤组束拉锥,一方面纤芯占空比过小,会严重影响光束质量,另一方面则需要较长的锥区来满足绝热拉锥条件以保持高传输效率,不利于后期操作,所以将采用氢氟酸腐蚀输入光纤的方法来增大TFB 的纤芯占空比,通过控制浸泡时间的长短来控制包层的厚度。
笔者利用仿真软件建立了3×1光纤功率合束器的模型,模型中合束器锥区设置为15 mm,腰区设置为5 mm,输出光纤长度设置为15 mm,根据光束传输法得到激光在功率合束器中的传播过程如图1所示,在TFB的锥区,激光基本限制在光纤纤芯内传播,泄漏至包层的光非常弱。激光进入TFB的腰区后,光从输入光纤的包层中泄露,与邻近光纤内的光耦合,但此时耦合程度较弱,而后激光通过熔点进入输出光纤,在输出光纤中耦合,激发出多种模式。
为得到光纤功率合束器的最佳制作参数,通过仿真计算了输入光纤的包层尺寸在80~200 μm范围内所对应的输出光束的M2和传输效率,其关系曲线如图2所示,由该曲线可知,该合束器的光束质量随着输入光纤包层尺寸从200 μm减小至130 μm而明显提升,但包层尺寸从130 μm继续减小,光束质量反而出现退化现象;同时合束器的传输效率也在输入光纤包层尺寸为130 μm时取得较大值。根据仿真结果,选择130 μm作为输入光纤包层尺寸,此时该合束器输出光束的M2因子和传输效率分别达到3.09和98.72%。
Research on high beam quality 3×1 fiber signal combiner
-
摘要: 在基于光纤功率合束器的高功率合成方案中,合成后激光保持好的光束质量是当前激光领域亟待解决的问题之一。实现了一种高光束质量光纤功率合束器的研制。首先,利用仿真软件建立3×1光纤功率合束器模型,对影响功率合束器光束质量和传输效率的因素进行了仿真,得到了制作合束器最佳参数的理论值;其次,基于光纤包层腐蚀技术,根据仿真结果利用熔融拉锥光纤束技术研制了一种输出光纤为50/400 μm (NA=0.12)的高光束质量3×1光纤功率合束器;最后,利用三台3 kW的光纤激光器对其进行了测试,在总输入功率为8.95 kW的情况下,合束后输出功率为8.62 kW,整体传输效率大于96%,光束质量M2=4.035。Abstract: In the high power synthesis schemes based on fiber signal combiner, it is one of the urgent problems to be solved in the current laser field to maintain good beam quality after beam combining. A kind of high beam quality fiber signal combiner was developed. Firstly, the model of a 3×1 fiber signal combiner was established by using simulation software, and the factors affecting the beam quality and transmission efficiency of combiner were simulated, and the theoretical values of optimum parameters of combiner were obtained. Secondly, based on the etched fiber cladding technology, a high beam quality 3×1 fiber signal combiner with an output fiber of 50/400 μm (NA=0.12) was fabricated by using the taper-fused fiber bundles technology according to simulation results. Finally, three 3 kW fiber lasers were used to test the combiner. Under the condition that the total input power is 8.95 kW, the output power after beam combining is 8.62 kW, the overall transmission efficiency is more than 96%, and the beam quality is M2=4.035.
-
Key words:
- fiber signal combiner /
- fiber laser /
- taper-fused /
- beam quality
-
-
[1] Dang Wenjia, Li Zhe, Lu Na, et al. Research progress of 0.9~1.0 μm near-infrared continuous-wave fiber lasers [J]. Chinese Optics, 2021, 14: 264-274. (in Chinese) doi: 10.37188/CO.2020-0193 [2] Fang Zeyuan, Yin Lu, Yan Mingjian, et al. Study on signal light transmission efficiency enhancement of backward pump-signal combiners in high-power fiber lasers [J]. Infrared and Laser Engineering, 2020, 49(10): 20200014. (in Chinese) [3] Wang Zheng, Yan Mingjian, Yin Lu, et al. Stripping of cladding light at different angles: theoretical and experimental studies [J]. Chinese Optics, 2019, 12(5): 1124-1130. (in Chinese) doi: 10.3788/co.20191205.1124 [4] Chen Zilun, Zhou Xuanfeng, Wang Zefeng, et al. Review of all-fiber signal combiner for high power fiber lasers(Invited) [J]. Infrared and Laser Engineering, 2018, 47(1): 0103005. (in Chinese) [5] Muendel M H, Farrow R, Liao K H, et al. Fused fiber pump and signal combiners for a 4-kW ytterbium fiber laser[C]//Processings of SPIE, 2011, 7914: 791431. [6] Eschrich T, Hoh D, Just F, et al. Incoherent beam combining of 5.1 kW using a 7×1 signal combiner into a 50 µm core output fiber [C]//Advanced Photonics, 2014: JTu6A. 1. [7] Plötner M, de Vries O, Schreiber T, et al. High power incoherent beam combining by an all-glass 7:1 fiber coupler with high beam quality[C]//Advanced Solid State Lasers, Shanghai, 2014: ATh2A. 17. [8] Lei Chengmin, Gu Yanran, Chen Zilun, et al. Incoherent beam combining of fiber lasers by an all-fiber 7×1 signal combiner at a power level of 14 kW [J]. Optics Express, 2018, 26(8): 10421. doi: 10.1364/OE.26.010421 [9] Yang Huan, Lei Chengmin, Wu Weijun, et al. 3×1 all-fiber signal combiner with high beam quality for high-power lasers [J]. Laser Physics, 2020, 30(2): 025102. doi: 10.1088/1555-6611/ab5d27 [10] Wu Weijun, Chen Zilun, Wang Zefeng, et al. Beam combining of fiber lasers by a 3 × 1 signal combiner at a power >13 kW [J]. Optical Fiber Technology, 2020, 54: 102109. doi: 10.1016/j.yofte.2019.102109 [11] Huang Shan, Liu Yu, Tao Rumao, et al. Lossless all-fiber 7×1 signal combiner for beyond 10 kW high power operation[C]//Jiang Huilin, Chu Junhao. Sixth Symposium on Novel Optoelectronic Detection Technology and Applications, 2020: 195. [12] Zhou Hang, Chen Zilun, Zhou Xuanfeng, et al. All-fiber 7×1 signal combiner for high power fiber lasers [J]. Applied Optics, 2015, 54(11): 3090-3094. doi: 10.1364/AO.54.003090 [13] Han Lixiang, Hao Mingming. Direct combining output of fiber coupled laser diodes via fiber combiner with high efficiency and multiple input ports [J]. Optik, 2020, 218: 165268. doi: 10.1016/j.ijleo.2020.165268