3.5 µm中红外超短脉冲掺铒ZBLAN光纤激光器关键技术研究

The research on mid-infrared fiber laser is one of these hot spots because of their potential applications in atmospheric gas detection, laser medicine, laser radar, mid-infrared imaging and electro-optical countermeasure system. The project applicant has achieved a word-record in graphene mode-locked fiber laser, high-power ultrashort-pulsed thulium-doped fiber amplifier at 2 µm wavelength, and high-power mid-infrared supercontinuum source at 2-5 µm wavelength. They also have a strong background in ZBLAN fiber cutting, end processing and thermal management. This project will work on a mid-infrared ultrashort-pulsed erbium-doped ZBLAN fiber laser operating at 3.5 µm wavelength region, and strive to achieve the world's first 3.5 µm mid-infrared ultrashort-pulsed fiber laser. The research work include: studying of the pulse dynamics process of passively mode-locked erbium-doped ZBLAN fiber laser; understanding of the relationship between pulse shaping mechanism and steady-state pulse in the resonant cavity of mid-infrared erbium-doped ZBLAN fiber laser; design and fabrication of graphene saturable absorber with high damage threshold; optimization of the conversion efficiency of 3.5 µm mid-infrared erbium-doped ZBLAN fiber laser using dual-wavelength pumping; and finally demonstration of a high-power and high conversion efficiency 3.5 µm mid-infrared ultrashort-pulsed erbium-doped ZBLAN fiber laser.

中红外光纤激光器在大气探测、激光医疗、激光雷达以及光电对抗等领域有着重要应用，成为近年来国际前沿性研究热点。项目申请人在石墨烯锁模光纤激光器、2 µm波段高功率超短脉冲掺铥光纤放大器、以及2~5 µm波段高功率中红外超连续谱光源等领域做了大量国际领先的前沿性工作，并在ZBLAN光纤的切割、端面处理以及热管理等方面具有良好的研究基础。本项目申请将对3.5 µm中红外超短脉冲掺铒ZBLAN光纤激光器进行系统的理论与实验研究，力争在国际上率先将超短脉冲光纤激光器的工作波段扩展到3.5 µm中红外波段。主要内容包括：研究中红外被动锁模掺铒ZBLAN光纤激光器的脉冲动力学过程；深入了解中红外掺铒ZBLAN光纤激光器谐振腔内脉冲整形机理与稳态脉冲之间的关系；高损伤阈值石墨烯可饱和吸收体的研制；双波长泵浦提高3.5 µm波段激光转换效率的优化；实现高功率高效率3.5 µm中红外超短脉冲光纤激光输出。

中红外光纤激光器可广泛应用于激光医疗、人眼安全雷达、非金属材料加工、光电对抗等众多领域，具有其它波段光纤激光器不可替代的重要作用。此外，高功率掺铥光纤激光器也是产生2~5 µm波段高功率中红外激光首选的泵浦源。本项目主要对中红外波段高功率超短脉冲掺铥光纤激光器、宽波长调谐范围被动锁模掺铥光纤激光器、高功率中红外光纤超荧光源进行了深入研究。主要研究工作和成果包括：. 利用光纤布拉格光栅作为滤波器来控制锁模掺铥光纤激光器的脉宽和光谱形状，结合纤芯泵浦高掺杂双包层光纤技术，实现了中红外波段高稳定性、线偏振、皮秒脉冲激光输出。利用该线偏振、皮秒掺铥光纤激光作为种子源，结合非线性脉冲放大技术，研制出了百瓦量级、全光纤结构、线偏振、皮秒掺铥光纤激光器，最高平均输出功率为240 W，偏振消光比>15 dB，脉冲宽度为45 ps。该结果为目前国际上2 µm波段全光纤结构超短脉冲激光器所产生的最高平均输出功率。. 实验搭建了一种全光纤结构波长可调谐被动锁模掺铥光纤激光器。该光纤激光器利用半导体可饱和吸收镜与高双折射率光纤环镜实现锁模皮秒脉冲与波长可调谐激光输出。高双折射率光纤环镜由一个2x2激光分束器和一段高双折射光纤组成，实验中通过改变光纤环镜中高双折射光纤的温度，从而得到了中心波长可调谐范围15nm，从1952 nm 到1967 nm，重复频率为29 MHz，最短脉冲宽度为6 ps的可调谐皮秒脉冲激光输出。. 利用光纤超荧光源与传统激光存在的本质区别，提出了利用窄线宽光纤超荧光作为种子源来抑制光纤放大器中的SBS效应。在国际上研制出了百瓦量级、全光纤结构、窄线宽、波长可调谐掺铥光纤超荧光源，使之成为一种兼具荧光及激光特性的新型高亮度光源。该工作为有效解决光纤放大器中的SBS效应问题指引了方向，为进一步高功率多光束光谱合束提供了新途径。