【作者】 周亚训；

【导师】 黄尚廉； 聂秋华；

【作者基本信息】 重庆大学 ， 光学工程， 2009， 博士

【摘要】 随着现代通信技术的飞速发展,人们对光纤通信容量和系统集成化的要求大大提高,这使得掺铒光纤放大器（Erbium-doped Fiber Amplifier,EDFA）与波分复用（Wavelength Division Multiplexing,WDM）技术的联合运用成为实现多波长和超长距离传输必不可少的条件。其中,EDFA已是提高WDM系统信道数和光纤通信容量的关键部件。目前,主要工作在C波段（1530-1565nm）区域并得到广泛应用的传统石英基EDFA已不能满足系统的发展需求。因此,开发具有宽带放大能力和极高单位长度增益的非石英基EDFA,直接实现C+L波段（1530¹610nm）区域宽带无缝放大,这对于WDM系统光纤通信容量的扩展以及系统集成化具有非常重要的实际意义。本论文结合当前光纤通信技术的发展需求,选择多组分宽带碲酸盐和铋酸盐重金属氧化物玻璃作为研究对象,基于自主实现从“宽带掺铒玻璃→宽带掺铒玻璃光纤→宽带掺铒玻璃光纤放大器”整个流程的研究考虑,围绕多组分宽带掺铒玻璃光谱性质的改性研究、多组分宽带掺铒玻璃光纤的研制和光谱性质测试、宽带掺铒玻璃光纤稳态和瞬态放大特性的理论研究三方面内容开展工作。论文的主要研究工作如下:1.开展了单掺稀土铒离子对于碲酸盐玻璃光谱特性的影响研究WDM系统的集成化趋势,需要尽可能地提高光纤放大器增益介质中的稀土铒离子(Er³⁺)掺杂浓度以便得到高的单位长度增益,但过高的铒离子掺杂也会带来一些负面效应,影响到光纤放大器的性能指标。因此,本文首先开展了稀土铒离子掺杂对于组分为TeO₂-ZnO-La₂O₃（Na₂O）碲酸盐玻璃光谱特性的影响研究,深入研究了1.53μm波段荧光谱、荧光强度和荧光寿命随铒离子掺杂浓度的变化关系。为此,论文运用Lorentz线型函数对测量到的荧光光谱进行了拟合分解,建立了一个等效四能级模型分析了各谱线成分相对强度随铒离子掺杂浓度的变化关系,剖析了1.53μm波段荧光谱的展宽及其荧光主峰转移现象。同时,基于Forster-Dexter能量转移理论,结合荧光俘获效应的影响,系统分析了激发态⁴I_13/2能级上铒离子无辐射能量衰减速率与其掺杂浓度的关系,从而指出了1.53μm波段荧光强度和荧光寿命在高掺杂浓度下发生猝灭的主要影响因素,并从无辐射能量转移机理出发分析对比了玻璃中稀土铒离子溶解性问题,计算得到了稀土铒离子的临界浓度和临界相互作用距离参数,确定了最佳掺杂含量。2.开展了多稀土离子共掺对于碲酸盐玻璃光谱特性的改性研究工作于1.53μm波段的掺铒光纤放大器通常采用1480或980nm波长进行泵浦。采用980nm波长泵浦,光纤放大器具有低的噪声系数,同时也存在着Er³⁺离子吸收较弱、上转换发光现象严重而引起的泵浦效率较低缺陷。本文从提高980nm泵浦效率和Er³⁺离子1.53μm波段荧光特性出发,开展了Er³⁺、Yb³⁺（镱）、Ce³⁺（铈）多稀土离子共掺对于组分为TeO₂-ZnO-La₂O₃-Nb₂O₅碲酸盐玻璃光谱特性的影响研究。论文通过具体分析Yb³⁺/Er³⁺离子间能量传递过程,研究了Yb³⁺离子掺杂对于Er³⁺离子1.53μm波段荧光和上转换发光的增强作用,并给予了理论模拟。通过分析Er³⁺/Ce³⁺离子间的能量传递过程,研究了Ce³⁺离子掺杂对于1.53μm波段荧光增强和上转换发光的抑制作用。从而指出相对于Er³⁺/Yb³⁺双掺形式,Er³⁺/Yb³⁺/Ce³⁺三掺是提高980nm泵浦效率和1.53μm波段荧光强度一种更加有效的组合掺杂方式。在此基础上,论文对基于声子辅助的Er³⁺/Ce³⁺离子间能量传递过程,首次提出了通过提高玻璃基质声子能量,减少能量传递过程中的能量失配程度,来进一步提高Er³⁺/Ce³⁺离子间能量传递速率的思想,实验结果得到了很好的印证。3.开展了单掺铒离子情形下铋酸盐玻璃荧光衰减特性研究OH-根离子不仅产生了石英传输光纤中1385nm波长附近的“水吸收峰”,同时也是掺铒玻璃中Er³⁺离子1.53μm波段荧光的一个主要猝灭中心。本文从测量分析Er³⁺离子1.53μm波段荧光衰减行为这一角度入手,开展了Bi₂O₃-B₂O₃-GeO₂-Na2O -Er₂O₃铋酸盐玻璃中OH-根离子与Er³⁺离子相互作用机理以及对Er³⁺离子荧光特性的影响研究。研究指出,Er³⁺离子与玻璃中残留的OH-根离子间能量转移导致低掺杂浓度下Er³⁺离子荧光呈现出明显的非指数衰减特征,运用Inokuti-Hirayama公式拟合得到了Er³⁺离子与OH-根离子间能量转移参数。同时,在玻璃高温熔融过程中注入干燥氧气进行了除水处理研究,除水处理能明显减少玻璃中残留的OH-根离子含量,从而提高Er³⁺离子1.53μm波段荧光强度以及掺铒光纤中的信号增益,而其荧光呈现出近似单一的指数衰减特征。4.开展了低声子能量掺铒铋酸盐玻璃中激发态吸收的抑制研究激发态吸收常发生在980nm泵浦下的一类低声子能量掺铒重金属氧化物玻璃中,它的存在制约了泵浦光转换效率的提高从而影响到Er³⁺离子1.53μm波段荧光特性。本文通过在组分为Bi₂O₃-GeO₂-Ga₂O₃-Na+2O一类低声子能量掺铒铋酸盐氧化物玻璃中分别引入Ce³⁺离子和B₂O₃组分,研究比较了这两种措施对于激发态吸收的抑制效果以及对于Er³⁺离子1.53μm波段荧光的作用。研究发现,适量Ce³⁺离子或B₂O₃组分的引入,分别通过能量转移和多声子弛豫方式提高了Er³⁺:⁴I_11/2→⁴I_13/2能级间无辐射弛豫速率,从而使得⁴I_11/2能级Er³⁺离子荧光寿命相应减小,激发态吸收得到有效抑制。同时,Ce³⁺离子的引入进一步提高了⁴I_13/2能级Er³⁺离子总量子效率,增强了1.53μm波段荧光强度。而B₂O₃组分的引入虽在一定程度上削弱了1.53μm波段荧光强度,但进一步展宽了其荧光发射谱。5.开展了新型多组分宽带掺铒玻璃光纤研制和光纤光谱性质研究在对多组分掺铒玻璃光谱性质改性研究基础上,本文选择合适的玻璃组分配比开展了新型宽带掺铒玻璃光纤的研制工作。论文利用自主的实验条件,采用旋转浇铸法和管棒组合法工艺研制了多组分宽带碲酸盐和铋酸盐玻璃光纤预制棒,拉制出了包层直径为125μm、纤芯直径分别为5.1μm和5.6μm的多组分宽带掺铒碲酸盐和铋酸盐玻璃光纤,并对得到的掺铒光纤进行了传输损耗和放大自发辐射（ASE）谱测试,1310nm波长处的传输损耗分别达到了3.7dB/m和3.4dB/m,ASE谱覆盖了C+L波段区域。在此基础上,论文鉴于多组分掺铒铋酸盐玻璃光纤与石英传输光纤熔化温度相差极大的特点,采用非对称熔接工艺进行了两者的熔接尝试,为下一步研制出高质量宽带掺铒玻璃光纤和光纤放大器积累了一定的工艺基础。6.开展了多组分宽带掺铒玻璃光纤稳态和瞬态放大特性的理论研究为进一步了解多组分宽带掺铒玻璃光纤的放大特性,同时为后续设计和优化宽带掺铒光纤放大器提供理论依据,本文从稳态和瞬态放大特性两个方面展开了系统的理论研究:1)建立了一个综合考虑Er³⁺离子能量转移和激发态吸收效应、以铋酸盐玻璃基掺铒光纤作为增益介质的铋基掺铒光纤放大器（Bi-EDFA）理论模型,分析比较了1480和980nm波长泵浦下放大器的稳态增益和噪声特性以及随信号输入功率、光纤长度的变化关系。同时,鉴于放大器内部存在着极大的由放大自发辐射产生的ASE噪声,论文从抑制噪声和再次利用噪声角度出发,对放大器进行了优化设计:①利用光隔离器抑制后向传输的ASE噪声,提高了放大器信号增益并降低了噪声系数。②利用光环形器引导前级放大产生的ASE噪声光泵浦一段后级低掺杂铋酸盐掺铒光纤,显著提高了放大器L波段信号增益;2)对于以碲酸盐玻璃基掺铒光纤作为增益介质的碲基掺铒光纤放大器（Te-EDFA）,理论研究了输入状态突变时放大器输出端信号功率的瞬态响应特性以及瞬态响应随信号输入功率、泵浦功率的演变关系。在此基础上,论文从抑制输出信号瞬态响应幅度出发,提出了调理脉冲输入信号阶跃型边沿为渐变型边沿的功率变化方式思想。研究揭示,提出的理论方案可以有效地抑制放大器输出端信号功率的瞬态响应幅度。最后,总结了全文研究工作和创新之处,指出了论文不足以及有待进一步深入研究的问题。更多还原

【Abstract】 With the rapid developments of modern communication technologies, the requests of the fiber communication capacity and system integration are increasingly improved, which makes the joint use between erbium doped fiber amplifier （EDFA） and wavelength division multiplexing （WDM） technology become an indispensable condition to realize the multi-wavelength and ultra-distance transmission. Of which, EDFA has become a key component to improve WDM system channels and communication capacities. However, traditional commonly-used silicate-based EDFA which works mainly in the C-band （1530¹565 nm） region has not satisfied the developing requests so far. Therefore, developing the nonsilicate-based EDFAs with broad amplifying bandwidth and high signal gain per unit length, and directly realizing the seamless amplification of （C+L）-band （1530¹610nm） region has a very important practical significance to the capacity expansion and integration of WDM communication system.Based on the developing requests of modern fiber communication technologies, and the considerations to realize the entire research processes, which start from the broadband erbium-doped glass to the broadband erbium-doped glass fiber and finally to the broadband erbium-doped fiber amplifier, the paper chooses the multi-component tellurite- and bismuth-based oxide glasses, and gives them a number of experimental and theoretical studies around the improved spectral characteristics of multi-component broadband erbium-doped glass, the fabrication of multi-component broadband erbium-doped glass fiber, and the steady and transient state theoretical simulations of broadband erbium-doped fiber amplifiers. The main works of the paper are as follows:1. The effect study of single-doped rare-earth erbium ion concentration on the spectral characteristics of tellurite-based glassThe integration of WDM system requires improving the rare-earth erbium-doped concentration in the gain media of fiber amplifier as possible as can in order to obtain a high signal gain per unit length. However, higher erbium-doped concentration can also bring some negative effects and finally affect the performance specifications of fiber amplifier. Therefore, the effect studies of erbium ion doped concentration on the spectral characteristics of tellurite-based glasses with the compositions of TeO₂-ZnO- La₂O₃（Na2O） are presented in this paper, and the 1.53μm band fluorescence spectra, fluorescence intensities and lifetimes have been detailed investigated as a function of erbium-doped concentration. To this end, the measured 1.53μm band fluorescence spectra are decomposed and fitted with Lorentz line-style function, the relative intensity variation of each spectral component are analyzed with a proposed equivalent four-level model, and the 1.53μm band spectral expansion and the emission peak shift with erbium-doped concentration are investigated. Meanwhile, the non-radiative energy transfer mechanism in the erbium-doped tellurite-based glass is studied according to the Forster-Dexter theory, and the main effect factor resulting in the quenching of 1.53μm band fluorescence intensity and fluorescence lifetime under the higher erbium-doped concentration is pointed out. Also, the rare-earth solubility in tellurite-based glasses with different compositions is compared, and the critical concentration and critical interaction distance of Er³⁺ ion are calculated based on the non-radiative energy transfer mechanism. Finally, the optimal doped content is determined.2. The improved study of the spectral characteristics for multi-rare earth ions co-doped tellurite-based glassOptical pumping of 1480 or 980nm wavelength is generally applied in 1.53μm band EDFA. EDFA has a low noise figure （NF） pumped at 980nm, but it also has a low pumping efficiency due to the weak absorption of Er³⁺ ion and the strong upconversion emission. To improve the 980nm pumping efficiency and 1.53μm band spectral characteristics, the Yb³⁺ and Ce³⁺ ions are respectively introduced into the erbium-doped tellurite-based glasses with the compositions of TeO₂-ZnO-La₂O₃-Nb₂O₅ in this paper. The enhanced effects of Yb³⁺ ions on the 1.53μm band fluorescence and upconversion luminescence of Er³⁺, which are in good agreements with the theoretical simulations, are investigated by analyzing the energy transfer process of Yb³⁺/Er³⁺, while the enhanced effects of Ce³⁺ ions on the 1.53μm band fluorescence and the suppressed effects of Ce³⁺ ions on the upconversion luminescence are investigated by analyzing the energy transfer process of Er³⁺/Ce³⁺. It is concluded that Er³⁺/Yb³⁺/Ce³⁺ tri-doped is a more effective scheme to improve the 980nm pumping efficiency and 1.53μm band spectral characteristics than Er³⁺/Yb³⁺ co-doped. Based on these, the paper also proposed a scheme for the first time to further improve the energy transfer rate from Er³⁺ to Ce³⁺, which is a phonon assisted energy transfer process, by increasing the host phonon energy and decreasing the energy mismatch between Er³⁺ and Ce³⁺ relevant transitions, and it is well illustrated by the experimental results.3. The study of fluorescence decaying characteristics for single erbium-doped bismuth-based glassIt is known that OH- groups incorporated in the glass are responsible for the hydroxyl absorption at about 1385nm in silicate-based transmission fiber, and are also one of the dominant quenching centers of 1.53μm band fluorescence of Er³⁺. Based on the measured 1.53μm band fluorescence decaying behavior, the interaction mechanism between OH- groups and Er³⁺ ions, and the effects of OH^- groups on Er³⁺ fluorescence in bismuth-based glass with the compositions of Bi₂O₃-B₂O₃-GeO₂-Na₂O are investigated in this paper. It is shown that the energy transfer from Er³⁺ ions to OH^- groups results in an evident non-exponential decaying behavior for glasses with low Er³⁺-doped concentration, and the energy transfer microparameters from Er³⁺ ions to OH^- groups are obtained by fitting the decaying curves with Inokuti-Hirayama equation. Furthermore, a removing OH- group treatment by pouring dry oxygen gas into the high-temperature glass melting is investigated. Removing OH- group treatment can dramatically decrease the OH- group content in the glass, and hence improve the 1.53μm band fluorescence intensity, while the fluorescence decaying reveals a nearly exponential behavior.4. The suppressed study of excited-state absorption for erbium-doped bismuth-based glass with low phonon energyThe excited-state absorption is generally occurred in 980nm pumped erbium-doped oxide glasses with low phonon energy, it limits the pumping conversion efficiency and hence 1.53μm band fluorescence intensity. Therefore, the Ce³⁺ ion and B₂O₃ component are respectively introduced into erbium-doped bismuth-based glass with low phonon energy, which has the compositions of Bi₂O₃-GeO₂-Ga₂O₃-Na2O. The effects of two suppressed schemes on the excited-state absorption and 1.53μm band fluorescence are investigated and compared. It is found that both a proper Ce³⁺ ion or B₂O₃ component content introduction into the glass increases the non-radiative relaxation rate from Er³⁺:⁴I_11/2 to ⁴I_13/2 levels by the means of energy transfer or multi-phonon relaxation and decreases the Er³⁺:⁴I_11/2 level lifetime, and hence the excited-state absorption is suppressed effectively. Meanwhile, the introduction of Ce³⁺ ions further improves the total quantum efficiency of Er³⁺:⁴I_13/2 level and 1.53μm band fluorescence intensity, whereas the introduction of B₂O₃ component further broadens the 1.53μm band fluorescence spectrum, however, its intensity is somewhat weakened.5. The study of multi-component broadband erbium-doped glass fiber fabrication and its spectral propertyBased on the above improved studies of the spectral properties for multi-component erbium-doped glasses, the fabrication studies of multi-component tellurite- and bismuth-based erbium-doped glass fibers are presented in this paper. Relying on the independent experimental conditions, the fiber performs are fabricated with the combined rotation-casting and tube-rode techniques, and the multi-component tellurite- and bismuth-based erbium-doped fibers with the cladding diameter of 125μm and the core diameter of 5.1μm and 5.6μm, respectively, are drawn. The transmission loss and the amplified spontaneous emission （ASE） spectra of broadband erbium-doped fiber are measured. The measured transmission losses at 1310nm are 3.7dB/m and 3.4dB/m for tellurite- and bismuth-based erbium-doped fibers, respectively, and both ASE spectra coverage the C+L band. Finally, considering the high melting temperature difference between the bismuth-based glass fiber and silicate-based transmission fiber, the splice between them is tried by non-symmetric splicing technique, and it is of a practical significance to accumulate a number of technique experiences in fabricating high-quality broadband erbium-doped fiber and EDFA.6. The theoretical study of steady and transient characteristics for multi-component broadband erbium-doped glass fiber amplifierIn order to understand the amplifying process and provide theoretical basis for the design of broadband EDFA, both the steady and transient state characteristics are investigated theoretically in this paper. 1) For the bismuth-based EDFA, a theoretical model considering the energy transfer among Er³⁺ ions and excited-state absorption is proposed, the steady-state signal gain, noise figure （NF） and their variations as a function of input power and fiber length pumped at 1480nm and 980nm wavelength, respectively, are stimulated and compared. Meanwhile, due to the large amplified spontaneous emission （ASE） noise, the optimal design of Bi-EDFA is studied by suppressing or utilizing ASE noise, respectively. It is found that by suppressing the backward ASE of Bi-EDFA with an optical isolator inserted in the bismuth-based erbium-doped fiber, the signal gain is increased and the NF is decreased. While an optical circulator is utilized to direct the unwanted ASE of the former Bi-EDFA to pump an un-pumped bismuth-based erbium-doped fiber, the L-band signal gain is enhanced evidently. 2) For the tellurite-based EDFA, the transient response and its variations as a function of input power and pumping power are investigated theoretically when EDFA is inputted with a pulse signal. Furthermore, in order to suppress transient excursion of the output signal, a novel scheme to modify the step edge of pulse signal into a slowly changed edge waveform signal is proposed for the first time. Compared to the pulse signal with step edge, it is shown that the transient excursion of Te-EDFA output power is reduced effectively when a properly designed, slowly changed edge signal is inputted.Finally, the paper works and innovation points are summarized, and some problems that are needed to be investigated further are pointed out.更多还原