波长灵活的石墨烯锁模拉曼光纤激光器研究

Ultrafast fiber lasers have found applications in scientific research, industrial processing, biology and medicine. Traditional active ion doped mode-locked fiber lasers can only operate at wavelengths of emission transitions. Here, we will study cw-pumped mode-locked fiber laser with gain provided by stimulated Raman scattering, to expand the laser wavelength to the regimes which are not covered by traditional fiber lasers. There were a few reports on mode locked Raman fiber lasers already in recent years. However, detailed theoretical and numerical study on mode locked fiber laser counting the special properties of Raman gain is still mission. In all reports, the laser performance is much worse than that of rare earth doped mode locked fiber laser. We will combine the shared property of ultrabroadband of graphene saturable absorber and Raman gain, so as to achieve real wavelength-versatile mode locked fiber lasers. The saturable absorber will be fabricated on single-mode-multimode-single-mode fiber structure, to achieve high stability and high damage threshold. After in-depth theoretical and numerical study of the mode locked Raman fiber laser, experiments at 1 and 2 micron will be carried out with objective of achieving high performance output and continuous wavelength tuning.

超短脉冲光纤激光器在科学研究、工业加工、生物医学等领域有重要应用。常规离子掺杂锁模光纤激光器的工作波长局限于能级跃迁，本项目拟研究基于拉曼增益的连续光泵浦锁模光纤激光器，把锁模激光工作波长拓展至常规离子掺杂光纤激光器不能覆盖的区域。近年来，已有一些这方面的研究，但是针对拉曼增益特殊性的锁模光纤激光器理论与数值模型尚无详细研究，报导的实验结果与相应的稀土离子掺杂锁模光纤激光器相比，性能差距不小。本项目结合同样有超宽谱特性的石墨烯可饱和吸收体和拉曼增益，以获得真正波长灵活的锁模光纤激光器。在研制稳定、高损伤阈值的基于单模-多模-单模光纤结构的石墨烯可饱和吸收体器件，深入的拉曼光纤激光器锁模机制理论与数值分析基础上，分别在1微米和2微米波段获得高性能的锁模拉曼光纤激光器，并研究其无失锁波长连续调谐。

超短脉冲光纤激光器在科学研究、工业加工、生物医疗等领域有重要应用。常规离子掺杂锁模光纤激光器的工作波长局限于能级跃迁，项目研究基于拉曼增益的锁模光纤激光器，把锁模激光工作波长拓展至常规离子掺杂光纤激光器不能覆盖的区域。在此总体目标下，开展了锁模拉曼光纤激光器的理论分析与新型锁模拉曼光纤激光器技术的研究。通过数值模拟和理论分析，清晰地理解了锁模拉曼光纤激光器与常规稀土离子掺杂锁模光纤激光器的不同之处。拉曼增益是一种非线性增益，泵浦激光的强度噪声会直接传递给拉曼激光，需要低噪声的泵浦源才能获得高稳定的锁模拉曼光纤激光输出。为此提出了采用放大自发辐射作为泵浦源，以提高锁模拉曼光纤激光输出的噪声特性。在验证实验中，获得了频谱信噪比高达85dB的超低噪声耗散孤子锁模激光输出。该工作为锁模拉曼光纤激光器的发展提供了一个崭新的思路，该想法也可被运用于常规锁模激光器中以提高噪声特性。另一方面，拉曼增益相对较弱，因此需要较长的增益光纤，导致更大的非线性相移和光纤色散的影响，使得锁模拉曼光纤激光器输出稳定脉冲的区间窄、更难以获得。为此提出脉冲激光同步泵浦是获得高性能锁模拉曼光纤激光输出的更优手段的想法。首次进行了主动锁模拉曼光纤激光器的研究，获得了基频与谐波锁模，研究了高阶拉曼过程对锁模的影响，并观察分析了锁模建立的动态过程。实现了石墨烯锁模拉曼光纤激光器，观察到了ns与ps级两种脉冲形式，发现锁模拉曼光纤激光器中无调Q巨脉冲。通过该项目的执行，在1.1-1.2微米，2.0-2.2微米获得了脉冲拉曼光纤激光，深入理解与发展了波长灵活的锁模拉曼光纤激光器技术。