Demonstration of mode splitting in an optical microcavity in aqueous environment

Scatterer induced modal coupling and the consequent mode splitting in a whispering gallery mode resonator is demonstrated in aqueous environment. The rate of change in splitting as particles enter the resonator mode volume strongly depends on the concentration of particle solution. The higher is the concentration, the higher is the rate of change. Polystyrene nanoparticles of radius 50 nm with concentration as low as 5 x 10(-6) wt % have been detected using the mode splitting spectra. Observation of mode splitting in water paves the way for constructing advanced resonator based sensors for measuring nanoparticles and biomolecules in various environments. (C) 2010 American Institute of Physics. [doi:10.1063/1.3481352]