Refractometric characterization of microsphere resonator based optical sensors

We have carried out the refractometric characterization on the whispering gallery mode (WGM) of a fused silica microsphere as the first step towards developing novel bio/chemical sensors with high sensitivity and high multiplexing capability. The WGM spectral position shifts when the refractive index of the surrounding medium is varied by adding ethanol to water. It is found that a sensitivity of 30 nm/RIU (refractive index units) and a refractive index detection limit on the order of 10^-7 RIU can be achieved. Theoretical calculation is also performed and agrees well with the experimental data