We show that manipulation by a spatial profile of the refractive index of a circularly symmetric dielectric cavity results in a novel way of fine tuning frequency separations as well as spatial localizations of high-<i>Q</i> whispering-gallery modes excited in the cavity. The method permits dispersion compensation in the modes (spectrum equalization), diminishes the quality-factor limitation by surface roughness and contamination, and allows critical coupling to ultra-high-<i>Q</i> modes without maintaining an air gap with evanescent couplers.
© 2003 Optical Society of America
Vladimir S. Ilchenko, Anatoliy A. Savchenkov, Andrey B. Matsko, and Lute Maleki, "Dispersion compensation in whispering-gallery modes," J. Opt. Soc. Am. A 20, 157-162 (2003)