Dispersive phase response in optical waveguide-resonator system

The authors report on the dispersive phase response of light traversing a tapered optical fiber coupled to the whispering-gallery modes (WGMs) of GaAs microdisks with cavity Q factors of up to 3×105 at wavelengths of around 1.5μm. The group delay of the coupled light, that is, a derivative of the phase shift, becomes positive (+10ps) and then negative (−55ps) near the high-Q WGM resonances, as compared with a reference group delay without evanescent-wave coupling. The chromatic dispersion becomes as high as ±8ns∕nm near WGM wavelengths.