Enhancing the sensitivity of a whispering-gallery mode microsphere sensor by a high-refractive-index surface layer
I. Teraoka and S. Arnold
J. Opt. Soc. Am., Vol. 23, No. 7 (2006)

highrefractive-index layer. With an increase in layer thickness, the photonic field of a WGM moves near the
sphere’s surface, while the peak in its radial distribution narrows, followed by backtracking and broadening.
During these changes, the resonance frequency decreases. The radial compression exposes a stronger evanescent
field to the surroundings, yet the mode retains a sharp resonance peak in the frequency domain. The
high-refractive-index layer will enhance the sensitivity of WGM frequency-shift sensors when used to detect
adsorption of molecules and a change in refractive index in the surroundings. A possibility to match resonance
shifts of different radial modes in the measurement of refractive indices is proposed.