Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1992-10-16
1993-12-21
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356 44, 25022718, H01J 516
Patent
active
052723348
ABSTRACT:
An apparatus for measuring temperature along an optical fiber uses backscattered light and optical time domain reflectometry to obtain a measure of the temperature distribution along the fiber. The ratio of anti-Stokes Raman to Stokes Raman backscattered light is used to determine the temperature distribution. In order to compensate for fluctuations in the wavelength of a laser source there is provided in a first embodiment an optical filter which passes Fresnel components of the light reflected from a distal end of the fiber. Changes in the ratio of the filtered Fresnel components correspond to changes in the source wavelength which may then be compensated by adjusting the source wavelength. In a second embodiment, the optical filter is used to measure the ratio of anti-Stokes Raman and Stokes Raman backscattered components derived from a reference temperature section of the fiber in which the temperature is held constant. Variations in this ratio result from source fluctuations which may again be compensated so as to maintain the laser source at a substantially constant output frequency thus permitting more accurate measurement of the temperature distributed along the fiber.
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Kingsley, Stuart A., "Distributed Fiber-optic Sensors," Proc. of the 1984 ISA Show, Houston, Tex. 22/25 Oct. 1984, pp. 315-330.
Dakin, J. P., et al., "Temperature Distribution Measurement Using Raman Ratio Thermometry," SPIE, vol. 566, Fiber Optic and Laser Sensor III (1985) pp. 249-256.
Kabushiki Kaisha Toshiba
Le Que T.
Nelms David C.
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