相位匹配下锥形光纤激发出的回廊模谐振

Excitation of Whispering Gallery Mode Resonances by a Phase-matched Fiber Taper

分别计算不同直径下锥形光纤基模和玻璃微球谐振腔内最低阶径向回廊模的传播常量,利用相位匹配条件,作出了锥形光纤与石英玻璃微球腔的直径对应关系曲线.在此基础上,选择锥腰直径2.8μm左右的低损耗锥形光纤与直径143.1μm球形度很好的玻璃微球腔进行近场耦合以激发球内的最低阶径向回廊模谐振,在锥形光纤的两端进行通光测试,在输出端获得了等间距分布的窄线宽滤波谱线,其吸收峰位置与利用Mie理论计算的球内最低阶径向回廊模谐振峰位置相一致.

The values of propagation constants of the mode in a fiber taper and for the lowest radial mode of whispering gallery mode （WGM） resonance in_ silica microspheres with different sizes are theoretically calculated. Using phase-matching relation, silica microsphere diameter required to fiber tapers with different diameters is determinated. Then to match the propagation constant of the mode in the fiber taper with low loss and waist diameter about 2.8 μm, a silica microsphere with diameter 143. 1 μm and good shape is chosen, and the taper-microsphere coupling system is set up for excitation of the lowest radial mode of WGM resonance. By injecting the laser power into the fiber taper, a transmission spectrum with narrow absorption peak and equal peak gaps is observed, and the absorption peak position is consistent with the lowest radial mode of WGM resonance position in the microsphere calculated by using the Mie theory. Based on the transmission spectrum, a high value of quality factor Q as 6 × 10^4 is measured in our taper-microsphere system.