高功率全光纤掺Yb³⁺光纤放大器传输放大特性研究

【作者】 许党朋；

【导师】 李明中；

【作者基本信息】 中国工程物理研究院 ， 光学工程， 2008， 硕士

【摘要】 高功率掺Yb³⁺光纤放大器以其结构紧凑、高效率、高光束质量、高信噪比等优点,广泛应用于科学研究、工业生产与军事等领域。尤其是高能固体激光装置的光脉冲产生系统要求输出具有一定光谱宽度、脉宽、高光束质量、高信噪比的高功率激光种子脉冲。高功率掺Yb³⁺光纤放大器主要决定了光脉冲产生系统的输出能量、光束质量、信噪比等系统关键输出参数,其增益是系统能流分布设计的关键环节,涉及到其他系统的增益分配。但光纤放大器中的ASE噪声、非线性效应以及饱和失真等因素严重影响了高功率掺Yb³⁺光纤放大器输出脉冲波形、光谱、能量以及信噪比等要求,因此,一方面,为保证光脉冲产生系统的输出能量、光谱带宽、信噪比及光束质量等指标;另一方面为保证整个光脉冲产生系统能够安全、高效、长期、稳定的运行工作,必须合理的设计该系统中高功率光纤放大器的工作点,并解决ASE噪声、饱和失真以及非线性效应等影响放大器输出的关键因素。论文针对光脉冲产生系统中高功率全光纤掺Yb³⁺光纤放大器,理论和实验两方面深入研究了其传输放大特性。主要解决了以下几个方面的问题:建立并完善了高功率掺Yb³⁺光纤放大器的理论;数值分析了高功率掺Yb³⁺光纤放大器的ASE噪声特性,脉冲的饱和放大特性与增益特性,结果显示通过选择增益光纤并合理设计放大器的增益,可以降低放大器中的ASE噪声功率,并且可避免饱和放大引起的脉冲波形失真;研究了高功率全光纤掺Yb³⁺光纤放大器的线性传输特性,分析了光纤放大器的损耗、增益光纤损伤阈值等,并提出了利用新型end-cap来解决光纤端面损伤的途径;研究了高功率全光纤掺Yb³⁺光纤放大器的非线性传输特性,数值分析了SPM、SRS以及SBS的阈值特性,研究表明根据输出功率要求,通过选择较短的大芯径增益光纤可以提高SBS和SRS的阈值,避免其对光谱产生的影响;为了避免超短脉冲波形与光谱在高功率掺Yb³⁺光纤放大器中引起的畸变,理论研究了高功率超短脉冲在掺Yb³⁺光纤中的自相似传输放大特性,结果表明当脉冲宽度、脉冲能量与放大器的增益满足一定关系时,超短脉冲在增益光纤中自相似传输放大,脉冲波形与光谱均演化为抛物形,输出脉冲呈线性啁啾,易于脉宽压缩,为高功率全光纤超短脉冲产生系统的研制提供了依据。基于理论分析,设计了高功率全光纤大模场掺Yb³⁺光纤放大器,实验中解决了泵浦光与信号光耦合技术、放大器级间隔离、噪声控制、饱和放大抑制、模式控制等难点,并通过增益光纤选择控制了光纤放大器中增益光纤的非线性效应与光纤损伤。通过对脉宽5ns的窄带脉冲放大,获得增益17dB,输出峰值功率700W;脉宽2.0ns,光谱带宽1.2nm的小宽带脉冲放大,获得增益33dB,输出脉冲峰值功率19.34kW。通过对高功率掺Yb³⁺光纤放大器传输放大特性的理论与实验研究,解决了泵浦光与信号光高效率耦合入纤问题,实现了系统的全光纤化;理论与实验解决了ASE噪声问题,提高了系统的信噪比;通过理论分析合理设计光纤放大器的工作点,避免了时间波形的饱和失真问题;理论分析了增益光纤损伤和非线性效应阈值,提供了设计光纤放大器时避免损伤与非线性效应产生的依据;目前实验中研制的光纤放大器样机已成功地应用于高能量固体激光装置光脉冲产生系统的功率光纤放大组件中,实现了高功率输出的全光纤光脉冲产生系统。更多还原

【Abstract】 High power ytterbium-doped fiber amplifier was found widespread application in scientific research, industry and military areas, due to its high compactness, high efficiency, high signal to noise ratio, good beam quality. In particular, the optical pulse generating system of high energy solid-state laser facility should provide the high-power seed pulse at 1053nm with good beam quality, high signal to noise ratio, and which must satisfy the certain temporal shape, spectral characteristic and polarization characteristic. The output energy, beam quality and signal to noise ratio of the optical pulse generating system were determined by high power ytterbium doped fiber amplifier to a certain degree, and the gain design of amplifier is the key component in the energy distribution of the whole system. However, the ASE noise, nonlinear effect and saturation distortion in the fiber amplifier had badly effect on output ability of the amplifier. Therefore, on the one hand, in order to ensure the output index of the optical pulse generation system, such as energy, spectral width, pulse duration etc, on the other hand, in order to ensure the whole optical pulse generating system to work safely and stabilitily in the longer period, it is very important to design the work point of the amplifier, and figure out the factor which had badly effect on the amplifier such as ASE noise, nonlinear effect and saturation distortion.In this paper, the amplification and transmission characteristics of the high power all fiber ytterbium-doped fiber amplifiers were investigated theoretically and experimentally. The mainly research results include: the theory of the high power ytterbium doped fiber amplifier was built; The ASE noise power characteristic and the saturation amplification characteristic of high power ytterbium fiber amplifier were numerical simulated,the results show that could reduce the ASE noise and avoid the saturation distortion by selecting the gain fiber and designing the gain of the fiber amplifier respectively; The linear transmission characteristics of the fiber amplifier were theoretically studied. The main loss in the amplifier, the damage threshold were analyzed, and the way that could be used to solve the fiber end face damage utilizing the end-cap device was introduced; The nonlinear transmission characteristics of the fiber amplifier were theoretically investigated. The threshold characteristics of SBS and SRS were numerical analyzed, the result show that the threshold of SBS and SRS were improved by selecting the shorter length and larger core diameter gain fiber; In order to avoid the utrashort pulse shape and spectral distortion in the high power ytterbium doped fiber amplifier, self-similar propagation and amplification of the high power ultra-short pulse in the ytterbium-doped large mode fiber were investigated, the results show that when the pulse duration ,energy and gain satisfied the certain relation,the utrashort pulse shape and spectral evolved into the parabolic shape, and the chirp was linear ,so the pulse can be compressed easily, which provided the theoretical basis and the promising way for realizing the all fiber high peak power ultra-short pulse generation system.High power LMA ytterbium-doped fiber amplifier was designed in the experiment based on the theoretical analysis. In the fiber amplifier, many difficult problems such as the coupling of the pump and signal light, the isolation between two stage amplifier, the noise manipulation and saturation amplification suppression were solved, at the same time, the occur of the nonlinear effect and the damage in the gain fiber were controlled by selecting the proper gain fiber in the amplifier. When the input pulse is narrow band and its duration is 5ns, the gain of the amplifier is 17dB, the amplified pulse power is 700W.when the input pulse duration and spectrum width are 2.0ns and 1.2nm respectively, the fiber amplifier reached the saturation state, at the same time the gain of the amplifier is 33dB, the peak power of the amplified pulse reached 19.34kW.Through the theoretical and experimental study of the amplification and transmission characteristics in the high power ytterbium doped fiber amplifier, the coupling problem of the high power pump and signal was resolved, and it is successful to realize the all fiber pulse generation system; the ASE noise problem was solved in the theory and experiment, the system noise was reduced dramatically; the threshold of the gain fiber damage and nonlinear effect were analyzed, which introduced the basis for the designing fiber amplifier to avoid the fiber damage and nonlinear effect; the sample fiber amplifier in the experiment was successfully applied in the power fiber amplifier module of the high power solid-state laser pulse generation system, which realized the high power all fiber optical pulse generation system.更多还原