为了满足光纤激光器在宽光谱高能量应用领域的要求，搭建了一种结构紧凑的光纤型宽光谱啁啾脉冲放大系统。将色散管理型锁模激光器产生的高斯型脉冲作为种子源，注入到正色散掺铒光纤放大器中进行自相似放大，脉冲将逐渐演化成抛物线型，此过程中脉冲的谱宽和能量都迅速增大。随后脉冲经色散补偿光纤的时域展宽，双包层铒镱共掺光纤的功率放大，透射光栅对压缩后实现了高能量的宽光谱输出。并结合理论模拟，优化了激光器的各元件参数，最终在中心波长1 560 nm处实现了光谱宽度为30 nm，平均功率为1.3 W，脉宽为587 fs，重复频率为40.1 MHz的宽光谱高能量激光输出。该激光器结构紧凑，稳定性好，对光学频率梳、光通信等应用领域具有一定研究价值。

The dispersive Fourier transform (DFT) technique opens a fascinating pathway to explore ultrafast non-repetitive events and has been employed to study the build-up process of mode-locked lasers. However, the shutting process for the mode-locked fiber laser seems to be beyond the scope of researchers, and the starting dynamics under near-zero dispersion remains unclear. Here, the complete evolution dynamics (from birth to extinction) of the conventional soliton (CS), stretched pulse (SP), and dissipative soliton (DS) are investigated by using the DFT technique. CS, SP, and DS fiber lasers mode locked by single-walled carbon nanotubes (SWNTs) are implemented via engineering the intracavity dispersion map. The relaxation oscillation can always be observed before the formation of stable pulse operation due to the inherent advantage of SWNT, but it exhibits distinct evolution dynamics in the starting and shutting processes. The shutting processes are dependent on the dispersion condition and turn-off time, which is against common sense. Some critical phenomena are also observed, including transient complex spectrum broadening and frequency-shift interaction of SPs and picosecond pulses. These results will further deepen understanding of the mode-locked fiber laser from a real-time point of view and are helpful for laser design and applications.

Real-time spectroscopy based on an emerging time-stretch technique can map the spectral information of optical waves into the time domain, opening several fascinating explorations of nonlinear dynamics in mode-locked lasers. However, the self-starting process of mode-locked lasers is quite sensitive to environmental perturbation, which causes the transient behaviors of lasers to deviate from the true buildup process of solitons. We optimize the laser system to improve its stability, which suppresses the Q-switched lasing induced by environmental perturbation. We, therefore, demonstrate the first observation of the entire buildup process of solitons in a mode-locked laser, revealing two possible pathways to generate the temporal solitons. One pathway includes the dynamics of raised relaxation oscillation, quasimode-locking stage, spectral beating behavior, and finally the stable single-soliton mode-locking. The other pathway contains, however, an extra transient bound-state stage before the final single-pulse mode-locking operation. Moreover, we propose a theoretical model to predict the buildup time of solitons, which agrees well with the experimental results. Our findings can bring real-time insights into ultrafast fiber laser design and optimization, as well as promote the application of fiber laser.