PHASE-MATCHED EXCITATION OF WHISPERING-GALLERY-MODE RESONANCES BY A FIBER TAPER

We show that high-Q whispering-gallery modes in fused-silica microsphe res can be efficiently excited by an optical fiber taper. By adjusting the taper diameter to match the propagation constant of the mode in t he taper with that of the resonant mode of interest, one can couple mo re than 90% of the light into the sphere. This represents a significan t improvement in excitation efficiency compared with other methods and is, we believe, the most efficient excitation of a high-Q microcavity resonance by a monomode optical fiber yet demonstrated. (C) 1997 Opti cal Society of America.