回音壁模式光纤激光器的阈值特性研究

研究了一种新型光纤激光器——消逝波激励的回音壁模式光纤激光器的阈值特性.将不同直径的石英光纤分别浸入低折射率的罗丹明6G乙醇和乙二醇混合溶液中，采用沿光纤轴向光抽运消逝波激励染料增益的方式，发现回音壁模式光纤激光辐射的阈值能量和混合溶液的折射率存在不同的依赖关系.随折射率的增加，对小直径光纤，阈值能量随之增加；对大直径光纤，阈值能量单调缓慢递减；对直径适中的光纤，阈值能量先减后增，存在一个和最小阈值能量对应的最佳折射率.用消逝波激励的回音壁模式激光理论，导出了回音壁模式光纤激光的阈值能量公式.理论计算曲线关键词：光纤激光器回音壁模式激光阈值消逝波

Threshold characteristics of evanescent-wave pumped whispering-gallery-mode fiber laser

The lasing threshold of evanescent-wave pumped whispering_gallery_mode （WGM） fiber lasers has been studied. Quartz fibers of different diameters were immersed in a mixed solution of ethanol and ethylene glycol doped by rhodamine 6G dye molecules, the refractive index of the solution was variable and lower than that of quartz fiber. We find that the dependence of lasing threshold on the refractive index of the mixed solution differs for different diameter of quartz fiber. With the increase of refractive index of the mixed solution from 1362 to 1432, the threshold energy decreases slowly and monotonicly for fibers of diameters larger than 296 μm, but increases for fibers of diameters smaller than 93 μm; for a fiber of diameter 197 μm, the threshold energy decreases slowly at first, and then increases sharply, there is an optimum refractive index of the mixed solution which matches a minimum threshold energy. Based on the theory of evanescent-wave pumped WGM fiber laser, we deduce a formula of lasing threshold, the calculated curves of lasing threshold are well consistent with the experimental data.