Fiber-optic sensors using high-resolution optical time domain instrumentation systems

Applications of high-resolution optical time domain instrumentation systems for the sensing of strain and temperature using optical fibers are discussed. It is demonstrated that optical fiber segmentation using partially reflective splices allows measurement of localized fiber parameters. In particular, localized fiber strain is measured using specially designed in-line reflectors spaced less than 1 m apart. It is shown that the time domain response to temperature variations can be improved by using silicone fluid-filled fibers with thermooptic coefficients as high as -4.2×10^-4/°C. The applications of fiber-optic reentrant loops to further improve on system-imposed measurement resolution are discussed. It is shown that recirculation of the probing optical pulse through the sensing fiber yields an effective increase in fiber interaction length