基于自发级联拉曼放大的中红外光纤激光器技术研究

Mid-infrared lasers have application in defense, medicine, remote sensing, and pollution monitoring etc. Cascaded Raman fiber laser has great potential in generating widely tunable mid-infrared lasers. At present, due to the availability of gain fiber and fiber components, mid-infrared Raman fiber laser is still not well developed. Based on our research experience in near infrared Raman fiber laser and initial results in mid-infrared Raman fiber laser, we propose to investigate spontaneous cascaded Raman amplification process for mid-infrared fiber laser generation. A high power pulsed 2 micron fiber laser is used to pump a piece of highly Ge-doped silica fiber, which can generate Raman-shifted light at 2.2~2.5 micron. Then, the laser will be injected to a piece of mid-infrared glass fiber, in which longer wavelength laser could be generated with spontaneous cascaded Raman amplification process. We will investigate the nonlinear optics processes in such laser devices and its impact on laser operation, and key technological issues. The overall goal is to solve the challenges in the technology of mid-infrared Raman fiber laser, and to achieve widely tunable laser output in the spectral range of 2~5 micron.

中红外波段的激光在国防、医疗、遥感、污染监测等领域有着重要应用。级联拉曼光纤激光器是产生宽调谐高功率中红外激光的潜力技术。目前，受增益光纤不成熟、光纤器件缺乏等限制，中红外拉曼光纤激光器在功率水平、波长覆盖范围等方面离应用需求尚有较大差距。在前期积累的近红外拉曼光纤激光器研究基础上，根据对中红外拉曼光纤激光器的预先研究的结果，本项目拟深入研究基于自发级联拉曼放大的中红外光纤激光器技术。具体来讲，采用脉冲2微米光纤激光作为泵浦源，通过高掺锗石英基光纤拉曼频移至2.2～2.5微米，再通过无需光纤光栅反射镜、波分复用器和隔离器等元器件的自发级联拉曼放大过程，在中红外玻璃光纤中获得更长波段的中红外激光产生。研究该类器件中的非线性光学过程及其对激光输出的影响，以及其它关键技术问题，以实现中红外拉曼光纤激光器技术突破，获得2～5微米波段宽调谐激光输出为总体目标。

中红外波段的激光在国防、医疗、遥感、污染监测等领域有着重要应用。级联拉曼光纤激光器是产生宽调谐高功率中红外激光的潜力技术。项目执行期间，针对将拉曼光纤激光器输出波长扩展至中红外波段的研究目标，进行了系统的自发级联拉曼光纤放大器和级联随机拉曼光纤激光器的研究。首先搭建了数值模型，仿真了2微米脉冲激光泵浦下，高掺锗石英光纤和硫化物光纤中自发级联拉曼放大过程，确定了高掺锗石英光纤在获得2-2.5微米拉曼激光方面的潜力和硫化物光纤在更长波段拉曼激光输出上的潜力。研制了高峰值功率的2微米脉冲光纤激光，泵浦高掺锗石英光纤，获得了最大波长2.48微米的可调谐中红外激光输出。与外单位合作，采用氟碲酸盐光纤，获得了宽谱、高平均功率的中红外超连续谱激光，最长波长4微米，输出功率达10W。基于氟碲酸盐光纤的中红外拉曼光纤激光研究尚在进行中。除此之外，也深入地研究了相关的另一类拉曼光纤激光器结构，级联随机拉曼光纤激光器。通过高阶级联随机拉曼光纤激光器，采用1微米激光作为泵浦，11阶拉曼频移获得了最大18W的2.13微米中红外光纤激光输出。详细研究了影响级联随机拉曼激光输出性能的因素，为后续在更长波的运用打下了基础。经过本项目研究，加深了对级联拉曼光纤激光器与放大器的理解，极大地扩展了光纤激光的输出波长范围。