Passively mode-locked fiber lasers based on a nonlinear polarization rotation (NPR) have attracted much attention due to their ability to generate short pulses with wide spectra and high peak power. However, environmental perturbations can easily cause the lasers to lose the mode-locked state and make it a challenge for practical application. The aim of this research is to improve the laser stability by inserting a Lyot filter into the mode-locked laser cavity. The experimental results indicate that the mode-locked state can be maintained when the radius of the fiber loop is changed from 7.5 to 1.5 cm, while the signal-to-noise ratio of the fundamental frequency remains almost the same. The tunability of the output power can be achieved by adding a half-wave plate (HWP) in the laser cavity without changing the pump power, while the mode-locked state remains stable. By adjusting the angle of the HWP2, the output power can be adjusted from 3.36 to 66.5 mW at repetition rate of 29.7 MHz.

中文翻译：

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NPR与Lyot滤波器混合结构作为可饱和吸收体的掺镱锁模光纤激光器

基于非线性偏振旋转（NPR）的被动锁模光纤激光器因其能够产生宽光谱和高峰值功率的短脉冲而备受关注。然而，环境扰动很容易导致激光器失去锁模状态，给实际应用带来挑战。本研究的目的是通过在锁模激光腔中插入 Lyot 滤波器来提高激光稳定性。实验结果表明，当光纤环路半径从7.5 cm变化到1.5 cm时，可以保持锁模状态，而基频信噪比几乎保持不变。通过在激光腔中添加半波片（HWP），可以在不改变泵浦功率的情况下实现输出功率的可调，同时锁模状态保持稳定。通过调整HWP2的角度，可以在29.7 MHz的重复频率下将输出功率从3.36 mW调整到66.5 mW。