Automated tracking of optical resonance shifts of dielectric micro-resonators

The whispering gallery modes (WGM) of dielectric microspheres can be leveraged to develop effective sensors. The WGM of a spherical optical cavity can be observed, for example, by introducing tunable laser light into the sphere through a tapered optical fiber. Laser light will circumnavigate the sphere due to total internal reflection and an optical mode (WGM) of the sphere will be observed at certain resonant wavelengths due to constructive interference. These resonance wavelengths will shift according to changes in sphere morphology. A new technique for tracking WGM shifts is presented. By analyzing the cross-correlation of separately acquired transmission spectra, WGM shifts can be determined and tracked. The cross-correlation algorithm is implemented in software, and the effectiveness is verified by a mechanical compression experiment. The cross-correlation method results in automated tracking with data output rates on the order of 540 Hz for real-time acquisitions and 10 kHz for post-processing.