【作者】 刘国华；

【导师】 刘德明；

【作者基本信息】 华中科技大学 ， 电子科学与技术， 2007， 博士

【摘要】 由于高功率双包层光纤激光器具有光束质量好、效率高、结构紧凑和散热性好等特点,近年来发展迅速,已广泛应用于光通信、激光加工、激光医疗和军事等领域。本论文利用数值模拟和理论分析的方法,对高功率掺镱双包层光纤激光器进行了深入系统的研究,为高功率光纤激光器的设计提供了理论依据。(1)根据高功率掺镱双包层光纤激光器的速率方程,推导出其近似解析式,并进行了数值模拟。研究了光纤中的激光和抽运光的分布特性,详细分析了光纤激光器的结构参量对输出特性的影响。(2)研究了LD尾纤与双包层光纤的侧面耦合,得到耦合效率与倾斜角的关系式,并进行了数值模拟。结果表明,存在一个最佳斜角,使得耦合效率取极大值。(3)建立了高功率掺镱双包层光纤激光器在多种抽运方式下的理论模型,推导出其近似解析式,并进行了数值模拟。研究了不同抽运方式对光纤激光器输出特性的影响。模拟结果表明,采用空间多点抽运方式,可以使抽运光在光纤中的分布更加平坦,从而使激光在光纤轴向上均衡地增大。(4)从热传导方程出发,推导出高功率掺镱双包层光纤激光器中温度分布的表达式,并数值模拟了光纤轴向和径向的温度分布。结果表明,采用空间多点抽运方式,可以使温度在整个光纤长度上均衡分布,而输出功率没有明显下降。选择适当的抽运光数目、合理设置抽运光注入位置,优化抽运光功率,可以降低光纤的温度,使温度分布更平坦。(5)研究了高功率双包层光纤激光器的受激喇曼散射和受激布里渊散射,利用打靶算法,对其进行了数值模拟。模拟结果表明,减小光纤长度、增大纤芯直径和降低掺杂浓度,可以提高受激喇曼散射和受激布里渊散射的阈值抽运光功率,从而抑制非线性效应。(6)研究了以闪耀光栅为色散元件的高功率掺镱双包层光纤激光器阵列的谱叠加技术,n个不同波长的激光束,经光栅衍射后在近场和远场重叠在一起,激光束的衍射效率>99%。(7)探讨了光热折变无机玻璃布拉格体光栅对宽谱、发散光束的衍射特性,研究了两束激光的体光栅谱叠加原理和技术,推导出衍射效率表达式,利用此式可以对体光栅的参量进行优化设计。(8)阐述了种子源主振荡放大光纤激光器的工作原理,并借助行波放大的暂态方程,对种子源脉冲放大进行了数值分析。更多还原

【Abstract】 The high-power Yb3+-doped double-clad fiber lasers (HPYDDCFLs) develop very fast in recent years for its advantages such as excellent beam quality, high efficiency, compact structure and good heat dissipation. The fiber lasers have been widely applied in the fields of optical communication, laser processing, medical treatment and military etc. In this dissertation, HPYDDCFLs has been studied in numerically and theoretically. These works provide a theoretical basis to the optimum design of HPYDDCFLs.(1) Based on the steady state rate equations of HPYDDCFLs, an approximate analytic function of distributed laser along the whole fiber is obtained. The distribution of pump power and laser power, and the dependence of the performance of HPYDDCFLs on the parameters are discussed.(2) The principal of angle side-coupling between LD and the double-clad fiber is studied. The relationship between coupling efficiency and angle is derived. The numerical results show there is an angle to maximize the coupling efficiency.(3) A theoretical model of HPYDDCFLs based on different pump modes is presented. An approximate analytic function of distributed laser along the whole fiber is obtained. The influence of pump mode on the performance of HPYDDCFLs is discussed. The numerical results show that laser power increase uniformly by utilizing distributed pump and optimizing the arrangement of pump powers.(4) According to the heat conduction equation, the expression about the distribution of temperature in HPYDDCFLs is derived. The axial and radial temperature distributions are numerically simulated. It has been shown that the distributed pumping scheme is best to dissipate heat uniformly in fibers and reduces operating temperature without significant output power degradation. The heat dissipation issue in HPYDDCFLs can be effectively solved by optimizing the arrangement of pump powers and pump absorption coefficients.(5) The theoretical analyses of stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in HPYDDCFLs are presented by solving the steady-state rate equations. Numerical results show that the SRS and SBS threshold power can be improved by shortening the cavity length, using large mode area fiber and lowering the Yb3+ concentration.(6) The outputs from an n-element HPYDDCFLs array have been combined into a single beam in the plane of the junction. This beam combining is achieved by use of a common external cavity containing a blazed grating, which simultaneously forces each array element to operate at a different, but controlled, wavelength and forces the beams from all the elements to overlap and propagate in the same direction. The grating diffraction efficiency is >99%.(7) Diffraction of the divergent beams with certain spectral width on VBG in inorganic photo-thermo-refractive glass is described. Design principles and technical approach for spectral combining of two HPYDDCFLs by VBG are developed. A mathematical model that reveals the critical parameters for high efficiency spectral beam combining by means of VBG has been presented. A general expression for the system efficiency can serve as a guideline when considering design issues of VBG.(8) The theory of the master-oscillator power amplifier (MOPA) is described. Numerical analysis of the transient-state of MOPA has been preformed.更多还原