【作者】 杨绩文；

【导师】 明海；

【作者基本信息】 中国科学技术大学 ， 光学， 2008， 博士

【摘要】 微结构光纤是近二十年发展起来的一种新型光纤,它具有许多独特的特性,如无穷尽单模传输、超大单模尺寸、大模场面积、可控色散特性等,可以避免高功率时非线性光学效应的产生、提高泵浦光的耦合效率、实现低损耗单模传输。在光通讯、高功率传输以及高功率激光放大器和激光器中有着广阔的应用前景。本学位论文的工作是大单模面积K9玻璃多孔微结构光纤设计及其掺铒放大器分析和瓣形微结构光纤掺铒与掺镱放大器分析。详细分析了多孔微结构光纤和瓣形微结构光纤的特性,设计了几种超大单模面积、低损耗的单模微结构光纤,建立了掺杂微结构光纤的放大模型,运用自主开发的掺杂微结构光纤放大软件,对其掺铒和掺镱的放大特性进行了详细分析,并探讨了其在高功率激光器和放大器中的潜在应用。本论文的研究工作和主要成果如下:1.将常规掺杂光纤能级速率方程与微结构光纤中本征模场归一化功率密度分布相结合,并考虑掺杂粒子数分布,推导出适用于掺杂微结构光纤稳态放大器的二能级和三能级速率方程和功率传输方程。开发了微结构准二能级和三能级掺杂光纤放大器分析软件,为掺杂微结构放大器和激光器提供一种很好的计算模型。2.结合K9玻璃光纤的易加工特性和高浓度掺杂特性,设计了一种芯径为20μm的多孔微结构K9玻璃光纤,通过分析得到其模式折射率n_c（λ）=1.516、单模直径D=21μm、模式面积A_eff=345.8μm²等参数,同时得到了在单模前提下其加工时的小孔偏差容许椭圆度容差为94.7%,最内层小孔的最大偏移量为0.1μm。3.详细分析了一种瓣形微结构光纤,讨论了其等效折射率分布以及色散曲线随光纤各参数的变化关系,找到一组单模尺寸大、基模损耗小、高阶模损耗快的瓣形光纤结构参数。在此瓣形微结构光纤中掺入铒离子,详细分析了掺铒瓣形微结构光纤的增益分布、阈值、泵浦分布和饱和功率等曲线,并计算了其噪声系数,通过比对相同掺杂的常规光纤,证明了它相对于常规掺杂光纤的优点:在比常规光纤模式面积大几十倍到一百倍的情况下,也具有与常规掺杂光纤相当的放大倍数,且噪声系数满足光纤放大器的要求。4.分析了掺镱瓣形微结构光纤增益分布、阈值、泵浦分布以及饱和功率等曲线,并计算了其噪声系数。通过比较常规掺镱光纤的单位面积非线性阈值,验证了在不产生非线性和光纤损伤的前提下单根掺镱瓣形微结构光纤可以支持很高的激光功率,并分析了掺镱瓣形微结构光纤在高功率激光器和放大器中的应用前景。本论文的主要创新点包括:1.引入掺杂微结构光纤的二能级与三能级的能级速率方程和功率传输方程,结合有限元法和平面波展开法,设计开发了一个大尺寸掺杂微结构光纤放大器的软件,为掺杂微结构光纤放大器和激光器提供了很好的计算。设计了一种高掺铒浓度的K9玻璃光子晶体光纤放大器,其单模芯径为21.6μm,在泵浦功率为500mW时,增益可达40dB。2.设计了掺铒和掺镱瓣形微结构光纤放大器,详细分析其放大特性。这种光纤放大器比常规光纤的单模尺寸大几十倍以上,能支持更高的激光功率。最高增益能达到37dB以上,最佳长度只有几米,噪声s系数≤4dB。通过非线性阈值模型和光纤损伤阈值,讨论了瓣形微结构光纤放大器在相干合束的应用,并分析了掺杂瓣形微结构光纤在高功率激光器和放大器中的应用价值。更多还原

【Abstract】 Microstructure fibers（MFs） have attracted much attention in the past twenty years, there are many special properties in MFs, such as endless single-mode, ultra large single mode core size, large mode area and controllable dispersion. MFs can avoid nonlinear optical effect, improve coupling efficiency of pump power and maintain low loss optical transmission in high pump and signal power. There are great potential applications in optics communication, high power optical transmission and high power amplifiers or lasers.The work in this dissertation is motivated by "Design of Ultra-large-core size single mode K9 photonic crystal fibers and analysis of K9-PCF amplifiers doped with rare earth ions" between University of Science and Technology of China and Xi’An Institute of Optics And Precision Mechanics Of CAS together with "Analysis of Segmented cladding fiber amplifiers" between University of Science and Technology of China and City University of Hong Kong. By analyzing the character of photonic crystal fibers and segmented cladding fibers, we design several ultra-large -core size single mode fibers with low loss, and analyze the rare earth doped MFs based on the model of rare earth doped MFs simulation and my own software about MFs amplifiers.The main research work and conclusions are as following:1. Based on the conventional rare earth doped fiber rate equations together with the normalized power density and population distribution, the rate equations of rare earth doped MFs are derived. Developing a software of rare earth doped MFs amplifiers, we provide a good simulation model of MFs amplifiers.2. We design a photonic crystal fiber at a core size of 20μm considering the advantage in processing and high doped concentration in K9 glass fibers, obtain its parameters such as: mode refracting index n_c（λ）=1.516, the single mode diameter D=21μm, mode area A_eff=345.8μm², and get its limit ellipticity ratio error is 94.7%, limit offset of inner hole is 0.1 um.3. We analyze a segmented cladding fiber, discuss its effective index distribution and dispersion curve, and obtain the parameters of a segmented cladding fiber with large single mode, small fundamental mode loss, large higher mode loss. Based on this fiber with Er³⁺ doped, we analyze in detail the amplification characteristics, and obtain its threshold pump power, pump power distribution and saturation output signal power. Finally we obtain its noise figure, and prove the rare earth doped segmented cladding fibers have many advantages comparing with conventional fiber, such as: the segmented cladding fiber has an mode area one hundred times larger than conventional fiber, its signal gain comparable with that of a conventional erbium-doped fiber, and its noise figure satisfy the requirement of fiber amplifiers.4. We analyze the amplification characteristics of Yb³⁺-doped segmented cladding fiber, and obtain its threshold pump power, pump power distribution, saturation output signal power and noise figure. By comparing the nonlinear power threshold in unit area with conventional Yb³⁺-doped fiber, we prove segmented cladding fiber can support high power. Finally, we discuss the potential applications in high power amplifiers and lasers.The innovative results in this dissertation are as following:1. By using the two-level and three-level propagation rate equations and power transmission equations in rare earth doped microstructure fiber, combing with Finite Element Method and Plane Wave Expansion Method, we design a software for rare earth doped microstructure fiber with large core size, which provide a good simulation tools for microstructure fiber amplifiers and lasers. We design a high concentration Er³⁺ doped photonic crystal fiber amplifier, whose single mode diameter is 21.6μm, the maximum gain can be 40 dB at a pump power of 500 mW.2. We design a microstructure fiber amplifier with Er³⁺ and Yb³⁺ doped, analyzing its amplification characteristics in detail, which has a dozens of times larger than conventional fiber, so can support much higher power. This microstructure fiber amplifier has a maximum gain of 37dB at several meters length, and its noise figure less than 4 dB. By nonlinear power threshold and damage threshold of fiber, we disscuss the application of microstructure fiber amplifier in coherent beam and the potential applications in rare earth doped high power fiber amplifiers and lasers.更多还原