808 nm LD激发下高折射率差光纤锥-硫卤微球耦合系统的荧光回廊模

Excitation of Fluorescence Whispering Gallery Modes in a Taper-Chalcohalide Microsphere Coupling System with a Large Refractive Index Difference Pumped by an 808 nm Laser Diode

用熔融淬冷法制备了0.5wt.%掺杂Nd^3＋：75GeS2-15Ga2S3-0CsI（0.5wt.%Nd-GGSI）硫卤玻璃.在此基础上以玻璃粉料漂浮熔融法制备出粒径为50-300μm高折射率（n≈2.1）玻璃微球,并在显微镜下选出表面质量高的硫卤微球用于后续实验.将火焰法拉制出的直径1-2μm间的双锥形石英微纳光纤与硫系微球进行近场耦合.相位匹配条件下测试结果表明光纤锥倏逝场将激发球内径向高阶回音壁模式.实验测量了在808nm LD激光泵浦下直径110μm微球的荧光光谱特性,结果表明：掺Nd3＋硫卤微球在输出端1 075nm波段附近产生了等间距分布的荧光回音壁模式的光学谐振,共振峰间隔为1.80nm.实验结果与微球腔回音壁模式谐振的理论模型有较高的符合度。

Chalcohalide glass based on the composition of Ge-Ga-S-CsI（GGSI）doped with Nd3＋（0.5wt.%）was synthesized with the traditional melt-quenching technique.The synthesized glass material was used to fabricate large refractive index（n≈2.1）microspheres using an improved flowing powders method.The fabricated spheres have diameters ranging from 50to 300μm.Microspheres with good surface quality were selected for the following coupling experiment.Biconical tapered fibers with waist diameters of 1~2μm were fabricated with a flame-heating process.They were then coupled with the selected GGSI glass microsphere via phase-matched evanescent waves.The phase-matching condition between the sphere and the fiber predicted high order radial modes in microsphere would be excited by the evanescent field of the fiber taper.In experiment,an 808nm Laser Diode（LD）was used as the excitation source and fluorescence emission spectra of the selected microsphere were measured.Periodically spaced intensity peaks around 1 075nm,which indicated Whispering Gallery Mode（WGM）optical resonances occurred in the Nd3＋doped GGSI glass microsphere,were clearly observed in experimental results.The typical spacing between two resonance peaks is 1.80nm,which is in good accordance with the theoretical prediction.