High-resolution spectroscopy of whispering gallery mode optical microcavities in the evanescent field of tapered optical fibers.*

Optical cavities with whispering gallery mode (WGM) resonances are interesting as building blocks for photonic devices, including fiber-integrated couplers and spectrometers, photonic crystals, and lasers. The high Q factors (10³-10⁶) along with their sensitivity to the surrounding environmental conditions allow the use of optical cavities as sensors of various physical quantities. We present results on polarized optical spectroscopy of spherical WGM resonant microcavities (D~5-50 micron) made of plastic, and silica and barium titanate glass, performed in air and water. The resonances were excited by evanescent light from optical fibers tapered either by chemical etching or by thermal pulling. The results of our experiments are consistent with theoretical predictions. We will discuss how to use these WGM resonances in order to apply forces to microparticles for microfluidic and biomedical applications.