全保偏非线性偏振环形镜锁模掺铒光纤激光器

研究了基于非线性偏振环形镜锁模的全保偏光纤激光器锁模机制。在非线性偏振环形镜中，用偏振分束器取代传统的非线性放大环形镜锁模激光器中的光纤耦合器，并辅以非互易性元件和增益光纤，作为全保偏光纤激光器中实现稳定锁模的核心器件。构建了一台基于非线性偏振环形镜的掺铒光纤锁模激光振荡器，实现了重复频率75 MHz，时域脉冲宽度141 fs，总输出功率约30 mW的稳定锁模脉冲序列输出。该激光器具有双向输出，且通过调节腔内波片可调节输出功率。此外，对激光器输出功率和重复频率的稳定性进行了评价，在自由运转情况下，1 h内输出脉冲序列的平均功率波动小于0.05%，重复频率的1 s相对稳定度为2.010-8。该结构的全保偏光纤激光器可开机自启动锁模，且环境稳定性高、重复频率较高、脉冲宽度窄，能满足激光测距、激光加工、激光光谱成像、航天等应用对超短脉冲光源的需求。

All-polarization-maintaining erbium-doped mode-locking fiber laser based on nonlinear polarization loop mirror

The mode-locking mechanism of an all-polarization-maintaining fiber laser based on a nonlinear polarization loop mirror was demonstrated. Instead of a fiber coupler in the traditional nonlinear amplifying loop mirror based mode-locked fiber laser, a polarization beam splitter (PBS) was implied in the nonlinear polarization loop mirror. The combination of the PBS, non-reciprocal components and a piece of gain fiber acted as the core elements in nonlinear polarization loop mirror to achieve stable mode-locking in an all-polarization-maintaining fiber laser. A passively mode-locked erbium-doped fiber laser based on this mode-locking mechanism was also presented. The laser directly emited an optical pulse train of 141 fs duration (75 MHz) with 30 mW total output power. The laser had bidirectional outputs, and the power from two outputs was adjustable by adjusting the waveplate in the cavity. Moreover, the environment stability of the free-running laser was characterized, yielding an average output power fluctuation of 0.05% in 1 h and the relative repetition rate stability of 2.010-8 in 1 s. The configuration enables self-start mode-locking, generating optical pulse trains with high environmental stability, high repetition rate and short pulse duration and fully meets the requirements of ultra-short pulse laser sources in femtosecond based ranging, laser machining, spectroscopy and other applications in spaceflight technologies.