【作者】 宁鼎；

【导师】 董孝义； 吕可诚；

【作者基本信息】 南开大学 ， 光学， 2001， 博士

【摘要】 本论文以掺Yb³⁺单包层和双包层光纤及其激光器为研究对象,开展了以下研究工作并取得若干创新性的成果: 1.掺Yb³⁺单包层和双包层光纤的研制（1）利用MCVD工艺、溶液掺杂法和光学机械加工技术,在国内首次研制出:掺Yb³⁺单包层光纤和大几何尺寸、大数值孔径内包层的双包层光纤（DCF）。掺杂浓度最高达3640ppm（重量比）。内包层的截面形状有圆形（CDCF）、方形（SDCF）和矩形（RDCF）,数值孔径为0.323⁰.360。（2）提出了DCF的设计原则。在实现高浓度、高质量Yb³⁺掺杂,降低纤芯中激光（1060nm）传输损耗和内包层中泵浦光（976nm）传输损耗方面采取了有效的技术措施,保证了光纤的质量。（3）按照ITU-T推荐的标准测量方法,测量了:光纤预制棒的几何尺寸、折射率分布,单包层和双包层光纤的几何参数、光学传输参数以及纤芯对泵浦光的吸收系数。采用包层模剥除技术,实现对DCF纤芯泵浦光吸收系数的直接测量,与单包层光纤测量数据比较,相对误差<5%。（4）通过ICP-AES法,测量了光纤中掺Yb3+浓度。实验确定了浸泡溶液浓度与掺Yb³⁺浓度之间的线性关系:1g/l的Yb₂O₃可掺入约767.8ppm的Yb³⁺。掺入浓度与976nm吸收系数也存在着线性关系:1ppm的Yb³⁺产生约4.11dB/km的吸收。2.以光纤激光器的基本原理为基础,采用新的模型导出DCF的有效吸收系数表达式,解释了DCF中吸收系数随长度等因素变化的特性; 用射线光学分析了:CDCF、RDCF和SDCF中光线传输的特点,对不同形状内包层的泵浦光吸收效率进行了讨论。3.掺Yb³⁺单包层光纤激光器的实验研究（1）通过对波长为976nm和915nm的两种泵浦方案的比较,确定976nm泵浦方案在1030nm的长波长区将获得更大增益。将980nmLD的中心波长向短波长移动了2nm,使976nm的泵浦光功率提高了10mW。（2）研制出FBG选频、全光纤化的线形腔掺Yb3+光纤（YDF）激光器。YDF的最佳长度为9m,入纤泵浦阈值功率为30.0mW,最大激光输出8.8mW,相对于入纤泵浦功率的斜率效率为70.4%,激光中心波长为1060nm,FWHM约为0.4nm。（3）研制出FBG选频、全光纤化的环形腔YDF激光器。YDF的最佳长更多还原

【Abstract】 The dissertation focuses on the Yb³⁺-doped single clad/double clad fibers and the fiber lasers, includes the detailed descriptions on the following subjects: 1. Study and manufacture of Yb³⁺-doped single-clad/double-clad fibers （1） By using MCVD process, liquid doping method and optical machining technique, we manufacture Yb³⁺-doped single-clad/double-clad fibers （DCF） firstly in China. The inner cladding of the Yb³⁺-doped DCF has big geometrical dimension and large numerical aperture. The doping concentration can reach as high as 3640ppm （weight ratio）. There are three kinds of inner-clad shape of DCF: circular （CDCF）, square （SDCF） and rectangular （RDCF）, and the NA of inner-clad is 0.323-0.360. （2） We put forward designing principle of DCF. By taking several effective measures, we obtain Yb³⁺-doped fiber having high concentration, high quality, low propagating losses at 1060nm（laser） in fiber’s core and 976nm（pump light） in inner cladding. （3） According to the standard measuring methods suggested by ITU-T, the following parameters are measured: the geometric dimensions and refractive index distributions of optical fiber performs; the geometric dimensions, optical propagation parameters and absorption coefficient at 976nm of single-clad /double-clad fibers. By using the technique of stripping clad modes, we measure the absorption coefficient about pump light in the core of DCF directly. By comparing with the data obtained from single-clad fiber, its relative error is less than 5%. （4） Using ICP-AES method, Yb³⁺ concentration is measured. Through experiments, we determine the linear relation between the concentration of immersion liquid and Yb³⁺ concentration: one gram of Yb2O3 in one liter of water can dope 767.8ppm Yb³⁺. Yb³⁺ concentration has linear relationship with the absorption coefficient at 976nm: 1ppm Yb³⁺ can produce 4.11dB/km absorption. 2. On the basis of fundamental principle of fiber laser and new model, we derive the representation of effective absorption coefficient and explain the characteristics of DCF: its absorption coefficient changes with fiber’s length and other factors. Using ray optics, the light propagation characteristics in CDCF, RDCF and SDCF are analyzed. At the same time, the pump absorption efficiencies are also discussed. 3. Experimental studies on Yb³⁺-doped single-clad fiber lasers （1） By comparing two kinds of pumping scheme, in which the wavelength are 976nm and 915nm respectively, we demonstrate that using 976nm pump source can lead to higher gain in the long wavelength region of 1030nm. Through adjusting the central wavelength of 980 LD toward short wavelength as long as 2nm, the pump power of 976nm is improved as high as 10mW. （2） We manufacture Fabry-Perot cavity Yb3+-doped fiber （YDF） lasers with FBG selecting frequency. The optimum YDF length is 9m, the launched pump threshold power is 30.0mW, the maximum laser power is 8.8mW and the slope efficiency with respect to launched pump power is 70.4%. The laser wavelength is 1060nm and the FWHM is about 0.4nm. （3） We manufacture ring cavity Yb3+-doped fiber lasers with FBG selecting frequency. The optimum YDF length is 12m, the launched pump threshold power is 30.2mW, the maximum laser power is 7.5mW and the slope efficiency with respect to launched pump power is 61.7%. The laser wavelength is 1060nm and the FWHM is about 0.2nm, which is 10% of the FWHM of the laser with mirror selecting frequency. The optimum coupling ratio of the output coupler is also discussed. 4. Experimental studies on Yb3+-doped double-clad fiber lasers （1） We design key components of DCF lasers. It is demonstrated that front-cavity mirror can improve the laser spectrum, increase the output power and the slope efficiency of laser and decrease the threshold . （2） Using CDCF with different length to make fiber lasers. It is found that there is an optimum fiber length in Yb3+-doped DCF laser and laser wavelength has linear relation with the length of DCF, changing ratio is 0.41nm/m. The relation between the laser wavelength and the fiber length is derived theoretically. （3） Using 20m long CDCF, SDCF and RDCF, the fiber lasers with different inner-clad shapes are made. By comparison, we find that the RDCF laser has the highest pump absorption efficiency, the lower launched pump threshold power （34.6mW）, the narrowest FWHM （less than 2nm） and the highest slope efficiency （77%）. （4） Using a group of back-cavity mirrors with different transmission ratio to constitute RDCF lasers, the changing regularities of some parameters （such as laser power, slope efficiency） with transmission ratio are studied. We obtain following conclusions: back-cavity mirror with a higher transmission ratio is better; back-cavity mirror can control laser wavelength; the relationship between slope efficiency and transmission ratio is in accordance with exponential function, the maximum slope efficiency is about 60%.更多还原