Whispering-gallery modes in a microsphere coated with a high-refractive index layer: polarization-dependent sensitivity enhancement of the resonance-shift and TE-TM resonance matching

Sensitivity enhancement of a whispering-gallery-mode microsphere resonance-shift sensor by coating of a high-refractive index (RI) layer is examined for TM polarization. The enhancement of sensitivity in response to particle adsorption or a RI change of the surroundings at the optimized layer thickness is greater for the TM mode compared with the TE mode, but the TM mode requires a thicker layer. A particular choice of the layer thickness allows the TE and TM shifts to match. Matching of the resonance frequency of the two modes is also examined. (c) 2007 Optical Society of America.