| 题名 | 多单频高功率光纤激光放大器理论和实验研究 |
| 作者 | 赵翔 |
| 文献子类 | 博士 |
| 导师 | 周军 |
| 关键词 | 光纤激光器，多单频信号光，光纤放大器，受激布里渊散射，偏振控制，光束质量 fiber lasers, multi-single-frequency laser, fiber amplifier, stimulated Brillouin scattering, polarization control, beam quality |
| 其他题名 | Theoretical and Experimental Study on Multi-single-frequency High Power Fiber Amplifiers |
| 英文摘要 | 高功率光纤激光器在工业制造和国防军事等领域有着广泛而重要的应用。基于相干组束和光谱组束的光纤激光高亮度组束技术，可以在大幅提升激光输出功率的同时保持良好的光束质量，突破光纤激光单纤单模输出功率受限的瓶颈。与常规的光纤激光功率合成技术不同，高亮度组束技术对参与组束的子激光器的光谱、偏振和光束质量等特性提出了非常高的要求。以多单频激光为种子光源的多单频光纤放大器，由于各个激光频率之间相互分立，大大提高了光纤放大器的受激布里渊散射（SBS）增强因子，可在保证光谱线宽的前提下，实现高功率高光束质量的放大激光输出，为高亮度组束提供性能优良的高功率激光光源。同时，通过控制各个频率之间的相位关系，多单频光纤放大器可以应用于二次谐波产生、相干激光通信、相干探测等领域，具有重大的研究价值和广泛的应用前景。 本论文主要围绕多单频信号光的高功率光纤放大技术，重点对多单频抑制光纤放大中的SBS效应以及放大器输出功率的提升，进行理论和实验研究，同时对偏振控制和模式滤波技术进行了探索研究。论文主要包括以下内容： 第一章绪论中，首先对高功率光纤激光器及其遇到的非线性效应进行了简要回顾。介绍了多单频光纤激光放大器的优势和多单频激光的产生技术。对多单频光纤激光放大器的发展现状和应用前景进行了概述，给出了国内外研究机构的典型进展，并进行了简要分析。 第二章研究了多纵模振荡腔放大结构及其自脉冲现象，分析了自脉冲现象的产生原因和危害，并对多纵模谐振腔的自脉冲特性进行了实验研究，包括不同功率、不同低反带宽等因素对于自脉冲强弱的影响。为了抑制多纵模振荡腔中的自脉冲现象，采用增加腔长和双腔结构两种方案进行了实验研究。 第三章主要研究了单频和三单频光纤放大器中SBS效应的抑制。建立了包含SBS效应的单频/三单频光纤放大器理论模型，分析了放大器中影响SBS效应的因素。搭建了高功率单模线偏振掺镱全光纤放大器实验系统，通过对增益光纤施加应力抑制SBS效应，实现了120 W的单频激光稳定运转。采用相位调制技术产生了三等高单频信号光，在考虑光纤自身热效应的基础上，三等高单频光纤放大器的SBS阈值提升至3.23倍。将相位调制生成多单频和应力梯度两种SBS抑制技术相结合，通过参数优化，实现了302 W的三单频单模线偏振光纤激光放大输出。通过AOM移频获得了两等高单频，研究了双频激光拍频产生光学载波射频信号的方法，在单模光纤放大器中对该双频激光进行功率放大，获得了功率为143 W、信噪比为53 dB的高亮度、高信噪比、高稳定的线偏振单模射频信号输出，这是目前我们已知亮度最高的光学载波射频信号。 第四章对基于相位调制产生多单频信号的高功率光纤放大器进行了研究。构建了不含时稳态的三波耦合方程，可同时考虑放大器中光纤的衰减和增益，以及光纤温度上升对SBS的影响等因素，对多单频光纤放大器中的SBS效应及其抑制进行分析。分析了多单频信号级联相位调制，包括独立级联和相关级联方法产生多等高单频（即平顶谱型）的可能性。对伪随机序列相位调制产生多单频及其功率放大进行了研究，在调制频率25.6 GHz，位数7位的情况下，采用20/400 μm的掺镱光纤放大器实现了779 W的功率输出，SBS阈值增强因子达到了30倍。 第五章研究了非保偏单模光纤放大器中的主动偏振控制技术，理论模拟了多种偏振噪声如波导形状、热致、弯曲、应力和扭曲等内外因素对于偏振态和偏振消光比的影响。搭建了非保偏单模光纤放大器实验平台，通过对信号光的主动偏振控制，在非保偏光纤放大器中实现了稳定了线偏振激光输出，偏振消光比达到了23 dB。 第六章针对大模场光纤放大器中的光束质量劣化和模式不稳定效应，提出了基于模式干涉和自再现效应的大小芯光纤模式滤波技术，分析了该模式滤波器中的光束传输和模式滤波原理，给出了模式滤波器的周期数、大小芯径的模场面积差等参数对高阶模滤除效果的影响，给出了不同基模比例下近场输出光场分布和光束质量因子。; Fiber laser has attracted tremendous applications in industrial processing, national defense and so on. High brightness beam combining technology including coherent beam combining and spectral beam combining has been proposed to break the limit of single fiber amplifier. Different from conventional beam combining technologies, high brightness beam combining technologies put forward higher requirements, such as narrower linewidth, higher degree of polarization and higher beam quality. Fiber amplifier seeded by multi-single-frequency laser could greatly improve the Stimulated Brillouin Scattering (SBS) threshold due to separation of each frequency, and it could become the high power laser source with high beam quality for high brightness beam combining on the premise of ensuring the narrow linewidth.Meanwhile, by controlling the phase relationship between each frequency, multi-single-frequency fiber amplifiers have significant research value and wide application prospects in the field of second harmonic generation, coherent communication, and coherent detection, etc. This dissertation focuses on the multi-single-frequency high power fiber amplifiers. Suppression of SBS effect and scaling of the output power in these amplifiers are theoretically and experimentally studied. Meanwhile, the polarization control and mode filtering approach are explored. Thesis mainly includes the following contents: Chapter one is an introduction to the overview of the development of fiber laser. The advantages and generated technology of multi-single-frequency laser are discussed. The development status and application prospect of multi-single-frequency are summarized, while some important research results reported by institution are listed and anlysised. Chapter two is a research of self-pulse phenomenon appearing in multi-longitudinal mode oscillator amplifier for high power output of multi-frequency laser. The causes and hazards of self-pulse phenomenon are analyzed. Self-pulse characteristics of the multi-longitudinal mode oscillator are experimentally studied, including the effects of different power operation and low reflective grating. Method of increasing the cavity length and the dual-cavity scheme are explored to suppress self-plusing phenomenon. Chapter three is a theoretical and experimental research of SBS effect in single/multi-single-frequency fiber amplifier. An numerical model of SBS effect is established to dicuss the influence factors on SBS effect. All-fibered single-mode linear-polarization fiber amplifier is built up and a stable single frequency laser operation of 120 W is achieved when longitudinal strain are applied to the gain fiber. Three-single-frequency with equal intensity by phase modulation are carried out, the SBS threshold could be increased to 3.23 times in consideration of the thermal effect in fiber amplifier. Under the combination of phase modulation and strain on SBS effect suppression, 302 W output power of three-single-frequency is achieved. The method of obtaining an optical carried radio-frequency (RF) signal by beating dual-frequency of equal intensity is introduced. The signal is then amplified by a single-mode fiber amplifier and 143 W RF signal with signal-noise-ratio of 53 dB is obtained, which is the currently highest brightness of optical carried RF signal to our best knowledge. Chapter four focuses on generating multi-single-frequency signal by phase modulation. A three-wave coupling equation without time domain are constructed and it could take the attenuation and gain of fiber into account, and also considering the temperation raise of the gain fiber on SBS suppression. The possibility of generating multi-single-frequency with equal intensity (top-hatted spectrum) is analyzed by cascaded phase modulation, including independent and related cascade phase modulation. An experiment is performed on PRBS phase modulation and power scaling. At the modulation frequency of 25.6 GHz and 7 bits, a 20/400 μm Yb-doped fiber amplifier is used to achieve 779 W output power, where SBS thereshold enhancement factor is increased by 30 times. Chapter five studies active polarization control technology in non-maintaining-polarization (NPM) fiber amplifiers. The effects of various polarization noise such as waveguide shape, thermal, bending, stress, and distortion on polarization state are simulated theoretically. A NPM single-mode fiber amplifier is set up and using active polarization control technique, steady polarization state is achieved with output polarization extinction ration reaching 23 dB. Chapter 6 focuses on the effects of beam quality cracking and mode instability in large mode area fiber, and a periodical large-small-large core (PLSC) mode filter based on mode interference and self-imaging effect is proposed to suppress high order modes. An investigation on the modeling of light propagation within this filter structure is presented. Influences of the parameters, such as the period number of the PLSC filter, the mode field area difference and combining other mode selected methods, on the filtering effect of the high order mode are given. The near-field output light field distribution and the beam quality factor under different fundamental mode ratios are also given. |
| 学科主题 | 光学工程 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31128]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 赵翔. 多单频高功率光纤激光放大器理论和实验研究[D]. |
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