拓扑绝缘体锁模拉曼光纤激光产生机理及实验研究

Passively mode-locked ultra-short pulses at 1.6-1.8 μm have attracted considerable attention due to their important applications in areas such as telecommunications, atmosphere monitoring, biomedicine and national defense. However, ultra-short pulsed lasers operating at this wavelength range are generally not available owing to the lack of appropriate laser gain medium and nonlinear saturable absorption mode-locking components. In this application, an effective lasing scheme is proposed for the requirement of ultra-short pulsed laser sources at this special wavelength range of 1.6-1.8 μm, by using a new ultra-broad nonlinear saturable absorber of topological insulator (TI) as the mode-locker in wavelength-flexible Raman fiber lasers. Different to traditional rare-earth-ion-doped mode-locked lasers with typical energy storage process, the SRS process in Raman fiber laser counterparts is characteristic of its immediate gain response and fast energy transfer. The broadband nonlinear optical properties of TIs will be investigated in this application. In addition, the mode-locked pulse building-up process in Raman fiber lasers is experimentally investigated including the impact of TIs’ specific parameters such as recovery time and modulation depth. The intrinsic relationship between the characteristics of the TIs and the time-frequency properties of ultrafast pulses will also be studied. Based on the qualified TI saturable absorber with appropriate parameters, potential to obtain a stable, broadly tunable laser emission in the particular wavelength range of 1.6-1.8 μm will be explored experimentally.

1.6-1.8 μm被动锁模超短脉冲激光在光通信、大气监测、生物医学、国防等领域具有重要应用，但因缺少合适的激光增益介质和非线性可饱和吸收器件，该波段的超短脉冲激光一般难于直接产生。本项目拟针对1.6-1.8 μm特定波段超短脉冲激光的应用需求，结合拓扑绝缘体的宽带非线性可饱和吸收特性，提出拓扑绝缘体可饱和吸收体锁模拉曼光纤激光器的技术路线。与传统稀土离子掺杂类锁模激光器脉冲建立过程不同，拉曼过程的能量转移和激光增益具有瞬时性，本项目将实验研究拓扑绝缘体的宽带可饱和吸收特性，探索拓扑绝缘体超快恢复时间、调制深度等参数对的拉曼光纤激光光源的锁模启动和脉冲建立过程的影响，揭示拓扑绝缘体各宏观参数与拉曼锁模脉冲时域频域特性的内在关系；在此基础上制备参数合适的拓扑绝缘体锁模器件，最终实现1.6-1.8 μm波段稳定、宽调谐的超短锁模脉冲激光输出。

1.6-1.8 μm被动锁模超短脉冲激光在光通信、大气监测、生物医学、国防等领域具有重要应用，但因缺少合适的激光增益介质和非线性可饱和吸收器件，该波段的超短脉冲激光一般难于直接产生。本项目针对1.6-1.8 μm特定波段超短脉冲激光的应用需求，结合拓扑绝缘体的宽带非线性可饱和吸收特性，提出拓扑绝缘体可饱和吸收体锁模拉曼光纤激光器的技术路线。项目执行期间取得的主要进展和成果包括：成功制备出高性能拓扑绝缘体用于拉曼锁模，实现了稳定的基于拓扑绝缘体可饱和吸收器件的百皮秒谐波锁模脉冲序列，并与基于非线性偏振旋转的拉曼锁模进行比较，探索拓扑绝缘体超快恢复时间、调制深度等参数对拉曼光纤激光光源的锁模启动和脉冲建立过程的影响，揭示了拓扑绝缘体各宏观参数与拉曼锁模脉冲时域频域特性的内在关系；在基本完成项目计划和指标的基础上，将拓扑绝缘体可饱和吸收体的工作波长进一步拓展到3μm波段，实验研究了中红外可调谐Er:ZBLAN调Q和锁模光纤激光器，并获得了宽波长范围可调的稳定脉冲序列输出，进一步验证拓扑绝缘体宽带工作特性和超快恢复特性。通过本项目的研究，对基于受激拉曼散射（SRS）非线性增益的新型激光器的锁模机理有了更深刻的认识，同时对拓扑绝缘体在特定波段的饱和吸收特性提供理论和实验依据，为发展新型特殊波段宽调谐超短超快光纤激光器件起到了参考和借鉴作用。基于项目执行期取得的进展和成果共发表高水平SCI论文13余篇，申请获得国家级、省部级项目共3项，培养硕士生2名、博士生1名。