光纤飞秒激光器凭借结构简单紧凑、鲁棒性好、免调节等优点，在工业、医疗、通信、科研等领域扮演着越来越重要的角色。近年来，各种新型激光材料、技术的出现，又进一步促进了光纤飞秒激光器的发展，各种性能指标得到了显著提升。然而在单路光纤飞秒激光器的高能量、窄脉宽、高稳定方向仍存在很大优化空间。基于此，本论文从全正色散全光纤锁模激光振荡器及脉冲同步泵浦光纤啁啾放大器两个层面开展相关理论和实验研究，研究结果对于构建高性能飞秒光纤激光系统具有重要意义，本论文主要研究内容及结果包括：一、构建了全正色散飞秒光纤振荡器的数值模型，模拟了锁模脉冲启动以及在腔内的演化过程，分析了限制单脉冲能量提升的多脉冲锁模，给出了针对单脉冲能量提升的技术方案；在激光器稳定性方向，利用主振荡方程数值模拟非稳态锁模输出：脉动孤子，发现腔内增益对锁模稳定性的重要影响。二、基于非线性环形放大镜（NALM）锁模的全正色散光纤振荡器实验研究。探究NALM环中增益光纤位置对称性对输出性能的影响，实现了单脉冲能量22 nJ、平均功率191 mW、压缩后脉宽195 fs的输出结果，为目前此类结构振荡器中最高的平均功率以及小于200 fs脉宽中最大的脉冲能量；在稳定性方向，利用色散傅里叶变换技术首次报道了脉动孤子的锁模启动过程，详细阐述了脉动孤子演化的非线性动力学，验证了腔内增益对锁模状态的重要影响，给出了非稳态锁模向稳态锁模的有效途径。三、光纤啁啾脉冲放大（CPA）系统的理论研究。首先分析了系统中重要组成和关键技术，仿真模拟了色散对自相位调制效应的补偿机制，基于此可以突破CPA系统B积分对脉冲峰值功率的限制，接着构建了脉冲同步泵浦啁啾脉冲放大的数值模型，能够解释放大过程中的脉冲畸变和光谱红移、窄化现象。最后进行实验验证，并与其他通用模型对比表明此模型具有更好的精确性。四、高能量光纤啁啾脉冲放大系统的实验研究。搭建了脉冲同步泵浦的光纤啁啾脉冲放大系统，实现了单脉冲能量112 μJ、重复频率1 kHz、压缩后脉冲宽度180 fs的输出结果，为当前严格意义全光纤飞秒激光器输出的最高单脉冲能量。并开展了棒状光子晶体光纤的放大实验，将能量进一步提升至1 mJ，压缩后脉冲宽度为231 fs，对应的峰值功率达4.3 GW。
Benefiting from the excellent characteristics of fiber including simple and compact structure, good robustness, high efficiency and alignment-free, femtosecond fiber lasers are playing an increasingly important role in many fields, such as industry, medical, communication, scientific research and so on. Moreover, in recent years, the emergence of various new laser materials and technologies has further promoted the vigorous development of fiber femtosecond lasers, and lasers’ performance have been greatly improved. However, there is still a lot of room for optimization in the direction of high energy, narrow pulse width and high stability of single-path fiber femtosecond laser. Based on this, relevant theoretical and experimental studies are carried out from two aspects: all-fiber all-normal dispersion mode-locked laser and pulsed synchronous pumped fiber chirped amplifier in this thesis. The research results are of great significance for the construction of high-performance femtosecond fiber lasers. The main research contents of this thesie are givern as follows:I. The numerical model of the all-normal dispersion fiber oscillator is constructed, and the build-up and evolution process in the cavity of the mode-locked pulse are simulated. The multi-pulse mode-locked which limitis the energy increase of the single pulse is analyzed, and the technical approach to break this limit is given. As for the laser stability, the unsteady mode-locked output, pulsating soliton, are numerically simulated via the main oscillation equation, and it is found that the gain in the cavity has an important effect on the mode-locked stability.II. The experimental studies of an all-normal dispersion fiber oscillator based on nonlinear amplifying loop mirror (NALM) mode-locking are carried out. The influence of the position symmetry of gain fiber in NALM ring on the output performance was investigated. The output results of single pulse energy of 22 nJ, average power of 191 mW and compressed pulse width of 195 fs were achieved, which are the highest average power and maximum pulse energy in a pulse width of less than 200 fs of this kind of structure oscillator. In the stability direction, the starting process of the pulsating solitons is recorded for the first time by using the dispersive Fourier transform technique, and the nonlinear dynamics of the pulse evolution during the process is described in detail. In addition, the important effect of the gain in the cavity on the state of the mode locking is verified, and an effective way from unsteady mode locking to steady mode locking is given.III. Theoretical studies on fiber chirped pulse amplification (CPA) system. First, we analyzed important and key techniques in CPA systems, and simulated the compensation mechanism of dispersion to self phase modulation effect. Based on this mechanism, we can breakthrough the limitation of the B integral on peak power in CPA systems. Second, we built a numerical model of the pulsed synchronous pumped fiber chirped amplifier, which can be used to explain pulse distoration, spectral narrowing and redshift during amplification. Finally, an experimental system is set up for verification, and compared with the results of other general models, it shows that this model has a better accuracy.IV. Experimental studies on high energy fiber CPA system. A pulsed synchronous pumped all-fiber chirped amplification system was set up, it can achieve single pulse energy of 112 μJ, repetition rate of 1 kHz, compressed pulse width of 180 fs, which is the highest single pulse energy among strictly all-fiber femtosecond lasers. As for the rod-type photonic crystal fiber amplification experiment, the output results of 1 mJ, 231 fs and 4.3 GW are achieved.
