Calorimetric fiber optic chemical sensor
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The present invention is directed to a sensor which utilizes an optical fiber interferometer to detect the absorption of a modulated laser beam by a particular chemical species. In particular, one embodiment of the present invention comprises a fiber optic system in which light from a continuously operating laser is modulated prior to passing through a region containing a chemical species of interest. Absorption of the light from the laser causes heating of the chemical species which, in turn, emits thermal energy that is transferred to an optical fiber that is situated in close proximity to the region in which the light is absorbed. In turn, the increase of the temperature of the optical fiber results in a change in the fiber's refractive index, thereby resulting in a change in the transmittance of said interferometer. The change in transmittance of the fiber is converted into an electrical signal in a photodetector. Thereafter, the modulated signal from the photodetector is recovered by phase-sensitive detection, using a lock-in amplifier. In this fashion, the amplitude of the output signal from the amplifier is proportional to the amount of light absorbed by the chemical species of interest. The concentration of this chemical species may thus be determined.
Taylor, Henry F. (1992). Calorimetric fiber optic chemical sensor. United States. Patent and Trademark Office; Texas A&M University. Libraries. Available electronically from