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 × 10 5 at wavelengths of around 1.5 μ m . The group delay of the coupled light, that is, a derivative of the phase shift, becomes positive ( + 10 ps ) and then negative ( − 55 ps ) near the high- Q WGM resonances, as compared with a reference group delay without evanescent-wave coupling. The chromatic dispersion becomes as high as ± 8 ns ∕ nm near WGM wavelengths.