【作者】 陈伟；

【导师】 陆培祥；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2011， 博士

【摘要】 本论文针对常规掺稀土光纤在光纤激光器应用实际工作中面临的三个科学问题,包括大芯径光纤与输出激光的光束质量问题、高效耦合问题及光暗化问题,展开研究。首先设计掺镱和掺铒光子晶体光纤的波导结构,构建出光子晶体光纤高温熔体流体力学模型,研究出光子晶体光纤的制备工艺；然后,制备出掺镱光子晶体光纤与掺铒光子晶体光纤,以及双包层光纤光栅,并分别将两种掺稀土光子晶体光纤进行了激光试验；最后,研究了超大模场掺镱光纤的制备与光束质量特性,分析了掺镱光纤的光暗化机理,研究了不同材料体系的掺镱光纤的光暗化特性,提出了相应的解决措施。。论文的主要研究内容与结果如下：(1)完成掺稀土光子晶体光纤的结构设计,发现在d/Λ≤0.30,Λ≤15λ时,大芯径光纤可以维持单模工作特性；外包层大空气孔径向尺寸w≥3λ,大空气孔之间的桥宽b≤0.5λ,可以获得高于0.7以上的内包层数值孔径,并制备出纤芯直径为43微米的大模场双包层掺镱光子晶体光纤,测试表明其具备单模特性,内包层数值孔径达到0.65,解决了大纤芯直径与单模工作特性的矛盾,以及高效耦合的问题。(2)系统研究掺稀土光子晶体光纤的制备工艺：建立高温熔体流体力学模型分析不同参数对工艺敏感度的影响,得出光子晶体光纤较佳拉丝工艺条件：高温炉温度为2123K,预制棒的进棒速度大于3mm/min,光纤拉丝速度大于200m/min,毛细管的内外压力差小于300pa。针对稀土离子传统液相掺杂工艺的缺陷,探索出稀土离子的全气相沉积工艺方法和完整的掺稀土光子晶体光纤制备工艺,并制备出掺镱光子晶体光纤和掺铒光子晶体光纤。(3)研究了双包层掺镱光子晶体光纤的激光特性：采用本论文设计并制备的掺镱光子晶体光纤和光纤光栅,构建出全光纤化的掺镱光子晶体光纤激光器,在915nm泵浦激光器作用下获得了中心波长为1080.2nm的3.96W的激光输出,斜率效率达到79.6%,光束质量因子M2为1.2。该掺镱光子晶体光纤光谱吸收特性优于常规掺镱光纤,其在915nm波长和976nm波长的吸收系数均高于常规掺镱光纤,在915nm波长的吸收峰较宽,其在两个吸收峰之间的谷底向长波长移动10nm。原因是空气石英玻璃网络电场对镱离子能级的产生了微扰,导致Stark分裂的新特性,影响了镱离子2F7/2→2F5/2的跃迁特性,从而产生了吸收谱的加宽与加高,以及吸收谷底向长波长的位移。(4)研究了掺铒光子晶体光纤及其激光放大特性,发现增大铒离子的掺杂区域,可以有效提升交叠因子,从而提升放大效率。掺铒光纤的激光放大特性与弯曲损耗特性试验结果表明：掺铒光子晶体光纤与普通掺铒光纤相比具有较高的增益特性、较好的增益平坦度、以及更好的抗弯曲性能,其原因在于空气与石英复合结构具备较大的交叠因子和较好地基模光场束缚能力。(5)研究了超大模场掺镱光纤：设计并制备出了全新结构的100微米级超大模场掺镱双包层光纤,激光试验发现受抑内全反射结构的超大模场光纤可以显著提升输出激光光束质量,该光纤激光在X、Y方向的平均光束质量因子M2分别为2.977和2.583,光束质量因子与常规大芯径光纤相比减小40%以上。(6)研究了掺镱光纤的光暗化特性：在分析光暗化机理的基础上,制备了不同材料配方的掺镱光纤。泵浦激光老化试验和激光功率稳定性试验表明：高镱离子浓度掺杂的掺镱光纤较为容易产生光暗化现象；而铝离子和磷离子的共掺剂引入的掺镱光纤,其光暗化效应显著降低。更多还原

【Abstract】 In this dissertation, the three scientific puzzles in the application fields of big power fiber laser for common rare-earth-ions doped optical fibers have been studied, including the problems between big core diameter and good laser beam quality, high coupling efficiency, and photo-darkening. Firstly, we design the waveguide structures for ytterbium-doped PCF and erbium-doped PCF, construct the hydrodynamics model for silica PCF high-temperature melt, develope the fabrication process route for PCF. Then, the ytterbium-doped PCF, erbium-doped PCF and double-cladding fiber gratings were manufactured. The laser experiments of the two kinds of PCF were earried out, and their performances were also analyzed. Finally, the ultra-mode-area ytterbium-doped optical fiber (YDF) was prepared and its laser beam quality was also studied. The mechanism of photo-darkening was construed, and the photo-darkening characteristics of different materials were also investigated, and the relevant countermeasures to reduce the photo-darkening were put forward.The research contents and results are formulated in the following.(1) The waveguide structures of rare-earth-ion doped PCF have been investigated. It is shown that the single-mode operation performance with large core for PCF can be acquired, the conditions are that the ratio of air hole diameter to lattice constant in the triangular array is smaller than or equal to 0.30, and lattice constant is smaller or equal to 15 times of transmission wavelength (λ). The cladding numerical aperture (NA) as high as 0.7 can be achieved at the condition that the radial size of large air-holes in the outer-cladding is larger than or equal to three times ofλand the bridge width is smaller than or equal to 0.5 times ofλThe double-cladding ytterbium-doped PCF with a core diameter of 43μm has been realized successfully, and tests demonstrate that the fiber could operate at the single-mode and the NA of inner-cladding reached 0.65, which can tackle the problems of large core and single-mode operation, and the high coupling efficiency. (2) The fabrication process technologies have been profoundly made research. The hydrodynamics model for silica PCF high-temperature melt has been constructed, and the influence disciplinarians of different parameters on the process sensitivity degree have been investigated, the preferable drawing conditions are that the furnace temperature is 2123K, the load speed of PCF perform is faster than 3mm/min, the fiber drawing speed is faster than 200m/min, and the pressure margin between outside and inner of capillary should be less than 300 pa. To the conventional solution-doping process deficiencies of rare-earth ions, the novelty all-gas-phase doping process for rare-earth-ions has been invented, the fabrication process route for rare-earth-doped PCF has been presented, and the ytterbium-doped PCF and erbium-doped PCF have been fabricated successfully.(3) The laser performances of double-cladding ytterbium-doped PCF have been studied. The all-fiber ytterbium-doped PCF laser has been constructed with self-make ytterbium-doped PCF and fiber grating. With the 915nm laser diode pumping, the output laser power at the center wavelength of 1080.2 nm is 3.96 watts, the slope efficiency is 79.6%, and the laser beam quality M2 is 1.2. The spectrum absorption characteristics of the double-cladding ytterbium-doped PCF are different from the common double-cladding ytterbium-doped optical fiber (DCYDF), its absorption coefficients at 915nm and 976nm wavelength are higher than that of the common DCYDF, the width of its absorption peak at 915nm wavelength is bigger than that of the common DCYDF, and the wavelength of its absorption valley is shifted 10nm to the longer wavelength. The reason may be that the ytterbium-ion energy levels are disturbed to some extent by the electric fields of the compounded air-silica glass network. This results in the novelty performance of Stark splitting, which influences the transition behavior of ytterbium-ions from 2F7/2 to 2F5/2.Therefore, the absorption spectra are widened and heightened, and the absorption valley shifts to the longer wavelength.(4) The research of erbium-doped optical fiber and its laser amplifying performances has been made. It is discovered that raising the doping domain of erbium-ions can efficiently increase the overlap factor and improve the amplifying efficiency. The laser amplifying experiments and bending loss tests of erbium-doped optical fibers show that the erbium-doped PCF has comparatively higher gain, better gain flatness and anti-bending ability than the common erbium-doped optical fiber. These results are attributed to the bigger overlap factor and better confining ability of fundamental mode light field for air-silica compounded structured materials.(5) The ultra-large mode-area ytterbium-doped optical fiber has been investigated. The novelty structure DCYDF with a core-diameter of 100μm has been designed and fabricated successfully. The lasers experiments show that the ultra-large mode-area ytterbium-doped optical fiber with Frustrated Total Internal Reflection structure can remarkably improve the laser beam quality. With this fiber, the average laser beam quality factor M2 in the directions of x and y are 2.977 and 2.583, which is 40% smaller than that of the common large-core YDFs.(6) The photo-darkening characteristics of YDFs have been investigated. On the basis of analyzing the photo-darkening mechanisms, the YDFs with different material prescriptions have been fabricated. The aging tests of pumping laser and laser experiments of output power stability have been carried out with these YDFs, the results show that the kinds of YDFs with high doping concentration of ytterium-ions are inclined to photo-darkening, and the aluminum-ions and phosphorus-ions co-doping agents can reduce the photo-darkening of the same-concentration YDFs.更多还原