Temperature measurements were made using a novel microoptical sensor based on dielectric microspheres that are excited by coupling light from optical fibers. The technique exploits the morphology-dependent shifts in resonant frequencies that are commonly referred to as the whispering gallery modes. A change in the temperature of the microsphere leads to a change in both the size and the index of refraction of the sphere which results in a shift of the resonant frequency. By monitoring this shift, the temperature of the environment surrounding the sphere can be determined. The whispering gallery mode shifts are observed by scanning a tunable diode laser that is coupled into the optical fiber on one end and monitoring the transmission spectrum by a photodiode on the other. When the microsphere is in contact with a bare section of the fiber, the optical modes are observed as dips in the intensity of the light transmitted through the fiber. Temperature measurements were made in both air and water using this novel technique. Measurements by the microoptical sensor were compared to those by thermocouples with good agreement between the two sets of results
The polarized transmission spectra of a fiber-microsphere system was investigated. Light from an optical fiber was side coupled into the dielectric microsphere through optical tunneling. It was found that the polarization of some of the light coupled into the microsphere and back into the fiber changed by 90°. The experiments showed a level of high signal-to-noise ratio peaks at the resonant frequencies in the polarized spectra and the possibility of discriminating between TE and TM modes of the microsphere.
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