掺镱双包层光纤放大器放大特性及其非线性现象研究
文献类型：学位论文
| 作者 | 常丽萍 |
| 学位类别 | 博士 |
| 答辩日期 | 2008 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 林尊琪 |
| 关键词 | 双包层光纤放大器 二能级理论模型 单频脉冲放大 百皮秒脉冲放大 非线性效应 |
| 其他题名 | Research on amplification behaviour and nonlinear phenomenon of the Ytterbium-doped double-clad fiber amplifiers |
| 中文摘要 | 光纤放大器由于其增益高、散热好、结构紧凑和可靠性高等诸多优点，在很多领域有着广泛的应用，是目前激光领域比较活跃的研究方向之一。传统单包层光纤放大器，存储能量有限，很难达到高功率输出；双包层光纤放大器具有适于大功率抽运，易实现高功率输出等优点, 在惯性约束核聚变（ICF）高功率固体激光驱动系统中有着更广泛的作用。掺镱双包层光纤放大器是“神光”高功率激光装置前端系统中多光路分束系统、时间精确同步触发系统和提高脉冲对比度系统中一个非常关键的技术单元。本论文围绕掺Yb3＋双包层光纤放大器（YDDCFA）开展了一系列理论和实验研究工作： 1.建立了包含放大自发辐射（ASE）的YDDCFA二能级速率方程，利用有限差分法，研究了其增益特性和ASE特性；并在忽略ASE的情况下，推导了YDDCFA小信号增益、功率增益和最优光纤长度解析式。得到如下结论： a)小信号放大(<5dBm)时，增益和噪声特性与抽运方式有关，前向抽运可获得更高的信噪比；大信号放大(>10dBm)时，输出功率与抽运方式无关； b)分析了不同抽运波长下的ASE功率和光谱特性，相同光纤长度下，选择吸收截面大的抽运波长，可改善输出功率的噪声特性，但同时应增加输入信号功率，以抑制反向ASE增长过快而损耗放大器存储能量； c)解析模型可直观的反映放大器参数与增益的关系，提出解析模型的适用范围：增益小于20dB。分析和总结了不同抽运波长和光纤长度下的增益变化特性，得到相同抽运波长下，激活光纤越长增益越高，但不能超过其最优光纤长度 。发现 主要由抽运功率和其吸收截面决定。 以上结论对YDDCFA的设计优化和实验现象分析有着重要的指导意义。 2.基于理论模型分析结果，选择抽运波长和光纤长度，搭建全光纤结构YDDCFA实验系统，分析了单频连续信号放大时的增益和噪声特性。 3.理论分析了YDDCFA 脉宽200ns脉冲放大时动态特性，数值模拟了影响脉冲波形畸变、脉冲输出能量的主要因素，为脉冲放大实验设计和实验现象的分析提供了一定的理论依据。 4.基于脉冲理论分析结果，实验研究了单频脉宽200ns的放大特性。峰值功率2W时得到1.7％rms的稳定性，满足了神光多光路分束系统中要求脉冲峰值功率1W，稳定性小于<3%rms的要求。实验中脉冲峰值功率3.3W时观察到后向受激布里渊散射（SBS）脉冲，分析了由SBS引起的脉冲波形畸变现象，采用F-P扫描干涉仪计算了SBS频移；提出DCFA中SBS阈值模型；得到SBS是单频脉冲放大过程中影响其输出脉冲峰值功率的主要因素。 5.实验研究了用于时间精确同步触发和脉冲清洁器的百皮秒脉冲放大模块，获得百皮秒脉冲输出能量2uJ，峰值功率20kW。分析了百皮秒脉冲放大过程中的受激拉曼散射（SRS）效应，利用单模光纤的色散作用分离了信号和SRS脉冲，得到SRS是制约百皮秒脉冲放大输出能量的主要因素。 6.自相位调制（SPM）是皮秒放大中的主要非线性现象，利用布拉格光纤光栅分析了皮秒单脉冲放大时SPM引起的光谱展宽效应；并发现在SPM和增益的共同作用下，小信号增益时，SPM引起信号光谱对称展宽，随着放大器增益饱和，脉冲形状变化，频率啁啾不再对称，频谱展宽量低频成分多于高频成分，蓝移峰较红移峰有较大幅值，光谱峰值波长向短波漂移。 |
| 英文摘要 | Fiber amplifier is one of the active research interests in the present laser field. It has broad applications in many areas due to high gain, easy thermal management, compactness and high reliability. The traditional single-clad fiber amplifiers are difficult to obtain high-power output because of the limited stored energy. While the double-clad fiber amplifiers with multimode inner cladding allow high efficient coupling of high pump power and are able to achieve the high-power output, which can take a great effect in the high power solid state laser system of ICF. Ytterbium-doped double-clad fiber amplifier (YDDCFA) is the key technical unit in the system of multi-pulse fiber splitters, the scheme of high-accuracy time- synchronization and the system for improving the contrast ratio of the laser pulse in the front ends for Shenguang high power laser facility. This thesis mainly focuses on the theoretical and experimental research of the Ytterbium-doped double clad fiber amplifiers (YDDCFA): 1.Constructing the two-level rate equations of the YDDCFA, including the amplified spontaneous emission (ASE). Using the finite-difference method, the gain and ASE property are investigated. In the case of neglecting the ASE power, the analytical model of small-signal gain, power-gain as well as the equation of the optimum fiber length is obtained. The main conclusions are as follows: a)For a small input signal (<5dBm), the characteristic of gain and ASE is dependent of the pump scheme. The forward pump provides the best signal-to-ASE ratio. For a large signal (>10dBm), the output power is nearly independent of the pump scheme. b)The power and spectral property of ASE is studied under the different pump wavelength. At the same fiber length, the ASE property of the output power can be improved when choosing a pump wavelength with the large absorption area. Meanwhile the input signal power should be increased to suppress the backward ASE power which rises too much to consume the stored energy of the amplifier. c)The analytic model can directly show the relation between the gain and the parameters of amplifiers, which is reasonable when the gain is below 20dB. The characteristic of gain is analyzed under different pump wavelength and fiber length. It can be concluded that at the same pump wavelength, the longer fiber length is, the higher gain of the amplifier can obtain, but can not exceed the optimum fiber length Lm. Lm is mainly determined by the pump power and the pump absorption area. These conclusions are of very importance for the design and the research of the experimental phenomenon of the YDDCFA. 2.Based on the theoretical results, the pump wavelength and fiber length is properly chosen to construct the experimental system of YDDCFA. The characteristics of gain and noise are analyzed on the amplification of single-frequency continuous wave signal. 3.The dynamic characteristics of 200ns pulse amplification are theoretically investigated. The factors which influence the pulse waveform distortion and output pulse energy of the amplifier are discussed. The results can build theoretical foundation for the design and research of the experimental phenomenon of the pulse amplifiers. 4.Based on dynamic characteristics of pulse amplification, the amplification of single-frequency pulse with pulse-width of 200ns is experimentally studied. The stability is 1.7%rms with the pulse peak power of 2W, which satisfies the requirement of the multi-pulse fiber splitter system of Shenguang (the peak power of 1W, the stability of less than 3%rms is needed). It is observed the backward Stimulated Brillouin Scattering (SBS) pulse in the experiment when the peak power is up to 3.3W, which can lead to the pulse distortion. Meantime the frequency shift of SBS is experimentally verified with the F-P interferometer. And the model of SBS threshold of DCFA is presented. It is obtained that SBS is the main factor which influences the output pulse peak power in the amplification of the single-frequency pulse amplification. 5.The hundred-picosecond pulse amplification module applied in the system of high-accuracy time-synchronization and pulse cleaner is experimentally studied. The pulse with the energy up to 2uJ and the peak power of about 20kW is obtained. The stimulated Raman Scattering occurred in the hundred-picosecond pulse amplification is also analyzed. The signal and SRS pulse are separated in use of the dispersion effect of the single mode fiber. SRS is the main factor to limit the hundred-picosecond pulse output energy. 6.Self Phase Modulation is the main nonlinear effect in the pulse amplification of ps regime. The spectral broadening of the amplification of single picosecond pulse is investigated with the Bragg fiber grating. Under the coupling effect of SPM and gain of the amplifier, the signal spectrum is symmetrically broadened at the small-signal gain. While the gain of the amplifier is saturated and the pulse wavefrom is distorted, the frequency chirp is not symmetric any more. SPM-induced spectral broadening is larger in the lower-frequency component than the higher frequency. And the blue-shifted peaks are more intensive than the red-shifted peak. The wavelength with the peak intensity is shifted to the short wavelength. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15223]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 常丽萍. 掺镱双包层光纤放大器放大特性及其非线性现象研究[D]. 中国科学院上海光学精密机械研究所. 2008. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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