Effect of a dielectric substrate on whispering-gallery-mode sensors

The effect of a dielectric substrate on whispering-gallery-mode (WGM)-based devices is experimentally investigated and theoretically quantified for spherical dielectric microresonators with similar to 5 mu m diameter. The interaction with a dielectric substrate yields a homogeneous broadening with a threshold-like behavior versus the azimuthal quantum number, which is accompanied by an energy renormalization of about 20% of the broadening. The WGM orbital planes of narrowest spectral linewidth (close to the Mie value) in the presence of a substrate are identified, and the consequences for the scattering spectrum analysis of microsphere devices relying on high-Q factors are discussed. (c) 2006 Optical Society of America