Observation of Whispering-Gallery Mode splitting in the spherical resonator

In order to characterize the fused-silica spherical resonator, an evanescent fiber taper coupling technique is employed. The coupling system consists of a fiber taper with a diameter of about 2.8 μm and a fused-silica spherical resonator with a diameter of about 143 μm. By injecting the laser power into the fiber taper, a transmission spectrum with narrow absorption peak and equal peak gaps is observed. After replacing the resonator by another one with the same diameter, whispering gallery mode splitting in the spherical resonator is observed. The peak gaps in the transmission become much smaller, which change from 3.7 nm to 0.32 nm.