Investigation into the fundamental principles of fiber optic evanescent sensors

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Virginia Tech


This investigation was concerned with the development of a fiber optic evanescent sensor. Such a sensor is based upon the lateral regions of the waveguide and their interaction with a chemical environment. The basic principles and concepts involved in the construction of a fiber optic spectroscopic evanescent field sensor are developed.

From this fundamental knowledge a series of sensors were constructed to characterize their responses. First, the response to simple refractive index changes and angle launch conditions were explored. This demonstrated the light interaction with the measurement environment. What followed was the use of these sensors to make spectrochemical absorption measurements suitable for a calibration curve of 1.25 x 10⁻² to 1.22 x 10⁻⁹ M concentrations for various dye systems.

As a consequence of the spectrochemical studies the unique interaction between the chemical environment and the silica surface was observed. This response is based upon the chemical reactivity of the silica surface and the chemical environment. This prompted the investigation of the ion exchange characteristics of the silica waveguide surface and the chemical environment. In this investigation the exchange selectivities of the alkali, alkali earth and lanthanide metals were determined.

Finally, a series of innovative fiber optic sensors base upon interferometric and refractometric measurements were investigated. These designs were based upon the fabrication characteristics of glass and plastic fiber optic waveguides.