FIBER OPTIC BIREFRINGENT THERMOMETER AND METHOD FOR MANUFACTURING THE SAME
First Claim
1. A fiber optic thermometer comprising:
- a light source assembly configured to generate light in a first spectral range and in a second spectral range, the first spectral range differing from the second spectral range;
a single-mode transmission fiber connected to the light source assembly and configured to carry the light of the first and second spectral ranges;
a polarizer configured to polarize light from the transmission fiber;
a polarization maintaining sensing fiber having first and second birefringence axes, wherein a birefringence of the sensing fiber between the first and second birefringence axes depends on a temperature to be measured, and the polarizer is configured to couple light from the light source into both the birefringence axes, the sensing fiber having a first end and a second end, and the polarizer being arranged between the transmission fiber and the first end;
a reflector arranged at the second end of the sensing fiber and configured to reflect light back into the sensing fiber;
a detector assembly configured to detect light returning from the sensing fiber through the polarizer and the single-mode transmission fiber, wherein the detector assembly is configured to generate a first signal A indicative of an intensity of returning light in the first spectral range and a second signal B indicative of an intensity of returning light in the second spectral range; and
processing circuitry configured to generate a temperature signal from the first signal A and the second signal B,wherein the processing circuitry is configured to calculate a temperature signal S from the first signal A and the second signal B that is an unambiguous function of the temperature over a desired temperature range.
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Accused Products
Abstract
A fiber optic thermometer is provided that uses a birefringent polarization maintaining sensing fiber as well as a single-mode transmission fiber for transmitting the optical signals between the sensing head and an optoelectronic module. The optoelectronic module contains two light sources operating at different spectral ranges. The unpolarized light from the light sources is sent through the transmission fiber, sent through a polarizer, and coupled into both birefringence axis of the sensing fiber. The waves are reflected at a reflector at a remote end of the sensing fiber, whereupon it returns through the sensing fiber, the polarizer and the transmission fiber. By analyzing the returned signal for both spectral ranges, a robust temperature signal can be derived. This thermometer design obviates the need for using a polarization maintaining fiber and polarization maintaining connectors between the optoelectronic module and the sensor head.
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Citations
27 Claims
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1. A fiber optic thermometer comprising:
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a light source assembly configured to generate light in a first spectral range and in a second spectral range, the first spectral range differing from the second spectral range; a single-mode transmission fiber connected to the light source assembly and configured to carry the light of the first and second spectral ranges; a polarizer configured to polarize light from the transmission fiber; a polarization maintaining sensing fiber having first and second birefringence axes, wherein a birefringence of the sensing fiber between the first and second birefringence axes depends on a temperature to be measured, and the polarizer is configured to couple light from the light source into both the birefringence axes, the sensing fiber having a first end and a second end, and the polarizer being arranged between the transmission fiber and the first end; a reflector arranged at the second end of the sensing fiber and configured to reflect light back into the sensing fiber; a detector assembly configured to detect light returning from the sensing fiber through the polarizer and the single-mode transmission fiber, wherein the detector assembly is configured to generate a first signal A indicative of an intensity of returning light in the first spectral range and a second signal B indicative of an intensity of returning light in the second spectral range; and processing circuitry configured to generate a temperature signal from the first signal A and the second signal B, wherein the processing circuitry is configured to calculate a temperature signal S from the first signal A and the second signal B that is an unambiguous function of the temperature over a desired temperature range. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A method for manufacturing fiber optic thermometer, the method comprising:
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arranging a light source assembly configured to generate light in a first spectral range and in a second spectral range, the first spectral range differing from the second spectral range; arranging a single-mode transmission fiber connected to the light source assembly and carrying the light of the first and second spectral ranges; arranging a polarizer configured to polarize light from the transmission fiber; arranging a polarization maintaining sensing fiber having first and second birefringence axes, wherein a birefringence of the sensing fiber between the first and second birefringence axes depends on a temperature to be measured, and the polarizer is configured to couple light from the light source into both the birefringence axes, the sensing fiber having a first end and a second end, and the polarizer being arranged between the transmission fiber and the first end; arranging a reflector arranged at the second end of the sensing fiber and configured to reflect light back into the sensing fiber; arranging a detector assembly configured to detect light returning from the sensing fiber through the polarizer and the single-mode transmission fiber, wherein the detector assembly is configured to generate a first signal A indicative of an intensity of returning light in the first spectral range and a second signal B indicative of an intensity of returning light in the second spectral range; arranging processing circuitry configured to generate a temperature signal from the first signal A and the second signal B, the processing circuitry being configured to calculate a temperature signal S from the first signal A and the second signal B that is an unambiguous function of the temperature over a desired temperature range; providing the sensing fiber to have an original birefringent retardation exceeding a desired birefringent retardation; sending light through the sensing fiber polarized along the first and the second birefringence axes of the sensing fiber; measuring a parameter depending on a current retardation in the sensing fiber; and permanently reducing the birefringence of the sensing fiber by tempering the sensing fiber until the parameter indicates that the current retardation is equal to the desired retardation. - View Dependent Claims (25, 26, 27)
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Specification