基于MOPA结构的黄光拉曼光纤激光器研究

In recent years, fiber yellow lasers have attracted enomous researchs due to the high demands for their applications in the modern biomedicine, medical cosmetology, food & drug testing, information storage, optical communication, defence, atmospheric remote sensing and et al.. In this proposal, an all fiber Raman yellow laser based on master oscillator power amplifier(MOPA) has been demonstrated in which the key problems being to be solved include single mode and single frequency output, high polarization extinction rate problem, and narrow line width lasing in Raman fiber laser seed and Raman fiber amplifier. To accomplish the goals put forward above, the evolvement process of a TEM00 mode Gussion beam during the propagation in the Raman fiber laser seed and subsquently the Raman fiber amplifier will be simulated by a numerical analytical method from optical power coupling equations. A theoretical model of fiber laser pumping fiber MOPA will be developed to deepen our standing. Based on the theoritical simulation, a 1178 nm Raman fiber laser seed pumped by 1120 nm fiber laser will be researched in which a high polarization extinction rate of 1178 nm laser will be achieved with the assistant of polarization maintaining fiber device of 45 tilt fiber gratings. To obtain high power narrow linewidth of 1178 nm signal light, some valid technology method will be used to suppress the stimulated Brillouin scattering(SBS) in high power Raman fiber amplifier. At last a laser at 589 nm with power level to an extent which allows practical uses will be achieved by second harmonic generation(SHG). The 589 nm laser system will be characterized by all fiber, high power output and compact structure. The theoretical and experimental work will be essential for further study of high power 589 nm Raman fiber laser.

光纤黄光激光器在生物医学、医疗美容、军工、大气遥感、食品药品检测、信息存储及通讯等领域有迫切需求和广泛应用，并因此吸引了极大的研究兴趣。课题围绕主振荡功率放大器（MOPA）结构的光纤拉曼黄光激光器的机理和研制进行，基于MOPA结构，利用掺镱光纤作为增益介质研制1120nm光纤激光器，经过包层泵浦放大后作为1178nm拉曼光纤激光器的泵浦源，控制种子激光的偏振和光束质量；采用数值解析方法研究基模高斯光束在种子激光器和放大器中的逐级演变过程，建立普适于光纤激光器泵浦MOPA激光系统的理论模型；掌握高功率光纤放大器中受激布里渊散射导致的信号光质量弱化机理，解决1178nm光纤放大器中谱线增宽问题，提高激光系统的拉曼增益；最终通过激光倍频技术实现高质量黄光激光输出。系统具有光纤化、高光束质量、结构紧凑的特点，该研究工作将推动国内光纤黄光激光器的研究，并为其今后的广泛应用奠定坚实的理论和技术基础。

为实现589nm黄光激光器系统，研制波长为1178nm的光纤激光器是前提。当前已可以直接发射1178nm激光，主要是基于光纤布拉格光栅的光子晶体光纤激光器或者是掺镱光纤激光器。由于1178nm光纤光栅掩膜版欠缺，需求稀少，国内尚没有1178nm光纤光栅买到。相比之下，更现实的实现1178nm光纤激光器的方法就是构建1120nm光纤激光器，然后泵浦拉曼光纤实现1120nm到1178nm拉曼频移。基于以上原因，获得高功率、窄线宽、高偏振消光比的1120nm光纤激光器吸引了大量的研究兴趣和报道。.我们尝试了掺镱光纤激光器直接发射1120nm激光的方法和利用MOPA技术将高质量1120nm种子光注入放大器获得高功率激光输出的方法。前者，我们自2013-2016年，相继将1120nm掺镱光纤激光器的输出功率从19.6mW提升至16.7W，获得激光线宽仅为0.02nm，是到目前为止，线宽最窄的1120nm光纤激光器；对于后者，为了保证1120nm光纤激光器的窄线宽、高光束质量特性，我们于2014年将19.6mW的1120nm激光作为种子注入掺镱光纤放大器中，获得2W的激光输出，功率提升效果不甚理想，原因在于种子光功率太低的缘故。在研究偏振1120nm光纤激光器时，发现并深入研究了双波长可切换1120nm光纤激光器。目前，我们用1120nm光纤激光器泵浦1178nm拉曼光纤激光器，初步获得1178nm信号光输出，后续的工作还需要大量时间和精力去完成。