基于全光注入调制的主动锁模掺铥光纤激光器关键技术研究

With the rapid development of 2 μm pulse laser applications in scientific research, industry, and military, improving the output pulse repetition rate and realizing flexible manipulation of thulium-doped fiber laser (TDFL) are significant challenges in the future. This project attempts to achieve actively mode-locked TDFL based on all-optical injection modulation, where pulsed pump light at 1.55 μm is injected to modulate the 2 μm oscillating signal in the cavity by using third-order nonlinear effect in optical fiber so that the output pulse repetition rate is synchronized to the pump light and output pulse width can be controlled by tuning the parameters of pump light. This project is aimed to comprehensive investigations of all-optical injection-modulated actively mode-locked TDFL from three aspects in terms of design and fabrication specialty fiber with high germania-doping in core, mode matching based on tapering splicing technique, and laser output tuning mechanism. Based on the development of specialty fiber which fulfills the requirement of group velocity matching over large wavelength span and highly efficient coupling between the specialty fiber and standard single mode fiber, experimental setup of actively mode-locked TDFL is possible to reveal the optical field evolution discipline in TDFL under all-optical injection modulation. The research outcome is expected to achieve tunable picosecond pulse with 10 GHz repetition rate output at 2 μm band.

随着2 μm波段脉冲激光在科研、工业及军事上应用的蓬勃发展，提高锁模掺铥光纤激光器的输出脉冲重复频率并实现灵活调控是未来的重大挑战。本项目拟采用全光注入调制实现对掺铥光纤激光器的主动锁模，利用1.55 μm波段的脉冲泵浦光通过光纤中的三阶非线性效应对腔内振荡的信号光进行调制，使激光器输出重复频率与高频泵浦脉冲同步，并且脉冲宽度可以通过对泵浦脉冲参数的调节进行控制。项目研究从纤芯高掺锗的微结构光纤设计与制备，基于拉锥熔接工艺的模场匹配到全光注入式主动锁模掺铥光纤激光器的调控机理三个方面展开。研制出能够在大波长跨度下满足群速度匹配的高非线性光纤并实现该光纤与普通单模光纤的高效耦合。在此基础上，构建基于全光注入调制的主动锁模掺铥光纤激光器实验装置，以期揭示全光注入调制下，激光器中光场的演变规律，力争在2 μm波段实现重复频率达10 GHz，脉宽可调的皮秒级脉冲输出。

传统2μm被动锁模光纤激光器受限于重复频率低和灵活调节方法缺失的问题，制约了其在高速可控场景下的应用。跨波段全光注入调制的主动锁模激光器具有调制速率高、输出脉冲灵活可调的优点，有望为2μm波段输出特性可调的高重频激光光源提供解决方案。基于上述优点，本项目围绕基于1.55μm注入调制的掺铥光纤激光器开展研究。完成了跨波段群速度匹配的高掺锗光纤设计，根据实际光纤加工工艺研制了掺杂浓度达75mol%的高掺锗光纤，测试结果表明该光纤截止波长大于6μm，1.55μm波段与2μm波段分别为正常色散和反常色散，满足全光注入与跨波段群速度匹配的需求。进一步设计了基于碲酸盐和氟化物的光子晶体光纤，提高了光纤非线性并扩展工作范围。研究了基于拉锥熔接工艺实现单模光纤与高掺锗光纤的高效耦合方法，通过控制束腰直径与拉锥长度，可在大波长跨度下的实现低损耗耦合。建立了全光注入调制的主动锁模激光器中腔内光场跨波段相互作用的动力学模型，得出注入调制、增益以及色散管理对输出脉冲的作用规律，论证了重复频率达40GHz、皮秒量级脉冲宽度、啁啾可控的输出特性，该方法可进一步扩展至中红外波段。此外，还对全保偏激光腔中的偏振演化锁模机理、基于高掺锗光纤的可重构多波长激光、全正色散激光器中的耗散孤子态演化过程、高确定性光孤子产生方法进行了探索研究，相关结果对稳定超快激光、可调连续激光、高能量激光脉冲、平滑光频梳产生等领域有重要价值。基于项目执行取得的进展和成果，共发表包含IEEE Journal of Lightwave Technology, Optics Express, IEEE Photonics Journal 等主流期刊在内的第一作者及通讯作者期刊论文15篇，申请专利8项，在学术会议上作邀请报告4次，培养研究生7名。