Method and apparatus for compensating fiber optic lead and connector losses in a fiber optic sensor by using a broadband optical source and multiple wave retardation
First Claim
1. Optical sensor apparatus, comprising:
- optical source means for providing a broadband source light beam including a plurality of spectral components, each spectral component having a different wavelength;
polarizer means for receiving said source light beam and polarizing it to provide a polarized light beam including said plurality of spectral components;
multiple wave retardation means for receiving said polarized light beam and retarding said plurality of components to provide a retarded light beam having a plurality of retarded components;
optical transducer means for (a) receiving said retarded light beam, (b) modulating said retarded components in accordance with an externally applied condition, each retarded component being modulated by an amount corresponding to the wavelength associated with each retarded component, and (c) providing an output light beam having a plurality of modulated components;
analyzer means for receiving said output light beam and providing an analyzed light beam having a plurality of analyzed components corresponding to said plurality of modulated components, a total light intensity of said analyzed light beam remaining effectively unresponsive to said externally applied condition;
filter means for (a) receiving said analyzed light beam (b) providing a first optical signal having only one portion of said analyzed components, said one portion including an analyzed component which varies according to said externally applied condition, and (c) providing a second optical signal including said plurality of analyzed components;
photodetector means for (a) receiving said first and second optical signals, (b) converting said optical signals into electrical signals, (c) providing a first electrical signal corresponding to an intensity of said first optical signal, and (d) providing a second electrical signal corresponding to an intensity of said second optical signal; and
processing means for receiving said first and second electrical signals and providing an output signal corresponding to a ratio of said first and second electrical signals.
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Accused Products
Abstract
Method and apparatus for compensating a phototransducer system for fiber optic transmission losses and optical source power fluctuations includes generating a broadband source light beam having a plurality of spectral components. The source light beam is transmitted to a polarizer which polarizes the light beam and directs it to a multiple wave retardation device. The retardation device retards the spectral components of the polarized light beam. The retarded light beam is injected into a photoelastic transducer which modulates the polarizations of the retarded light beam in accordance with pressure applied to the transducer. Each spectral component of the retarded light beam will be modulated by the transducer. However, the broadband light beam will remain, in sum, relatively invariant to the applied pressure. The modulated light beam is then passed through an analyzer, injected into a fiber optic cable, and transmitted to a beam splitter. The beam splitter provides a first light beam to a photodetector which detects the light intensity of all spectral components, which intensity is only affected by transmission losses and power fluctuations within the system. A second portion of the split light beam is passed through a narrow passband filter which passes only certain portions of the spectral components which do vary with the applied pressure and transmission losses and power fluctuations. The filtered signal is detected by a second photodetector. The photodetectors provide electrical signals to a processor which outputs an electrical signal corresponding to a ratio of the first and second electrical signals.
21 Citations
27 Claims
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1. Optical sensor apparatus, comprising:
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optical source means for providing a broadband source light beam including a plurality of spectral components, each spectral component having a different wavelength; polarizer means for receiving said source light beam and polarizing it to provide a polarized light beam including said plurality of spectral components; multiple wave retardation means for receiving said polarized light beam and retarding said plurality of components to provide a retarded light beam having a plurality of retarded components; optical transducer means for (a) receiving said retarded light beam, (b) modulating said retarded components in accordance with an externally applied condition, each retarded component being modulated by an amount corresponding to the wavelength associated with each retarded component, and (c) providing an output light beam having a plurality of modulated components; analyzer means for receiving said output light beam and providing an analyzed light beam having a plurality of analyzed components corresponding to said plurality of modulated components, a total light intensity of said analyzed light beam remaining effectively unresponsive to said externally applied condition; filter means for (a) receiving said analyzed light beam (b) providing a first optical signal having only one portion of said analyzed components, said one portion including an analyzed component which varies according to said externally applied condition, and (c) providing a second optical signal including said plurality of analyzed components; photodetector means for (a) receiving said first and second optical signals, (b) converting said optical signals into electrical signals, (c) providing a first electrical signal corresponding to an intensity of said first optical signal, and (d) providing a second electrical signal corresponding to an intensity of said second optical signal; and processing means for receiving said first and second electrical signals and providing an output signal corresponding to a ratio of said first and second electrical signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. Optical sensor apparatus, comprising:
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light source means for providing a source light beam having a plurality of spectral components, each spectral component having a different wavelength; polarization-multiple wavelength retardation-transducer means for (a) receiving said source light beam, (b) polarizing said source light beam to provide a polarized light beam having said plurality of spectral components, (c) retarding said plurality of spectral components in said polarized light beam to provide a retarded light beam having a plurality of retarded components, (d) modulating said retarded light beam in accordance with externally applied pressure to provide a modulated light beam having a plurality of modulated components corresponding to said plurality of retarded components, and (e) analyzing said modulated light beam to provide an output light beam having a total light intensity which is effectively unresponsive to said externally applied pressure, said output light beam having said plurality of modulated components; filter means for (a) receiving said output light beam, (b) providing a first optical signal having only one portion of said plurality of modulated components, said one portion varying in accordance with said externally applied pressure, (c) providing a second optical signal corresponding to said unresponsive total light intensity; photodetector means for receiving said first and second optical signals and providing first and second electrical signals corresponding to light intensities of said first and second optical signals, respectively; and processing means for receiving said first and second electrical signals and providing an output signal corresponding to a ratio of said first and second electrical signals. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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20. A method of sensing comprising the steps of:
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providing a source light beam having a plurality of spectral components, each spectral component having a different wavelength; polarizing said source light beam to provide a polarized light beam having said plurality of spectral components; retarding said polarized light beam to provide a retarded light beam having a plurality of retarded components corresponding to said plurality of spectral components; modulating said retarded light beam in accordance with an externally applied condition to provide a modulated light beam having a plurality of modulated components corresponding to said plurality of retarded components, each said modulated component being modulated by an amount corresponding to the wavelength associated with each retarded component; analyzing said modulated light beam to provide an analyzed light beam having a plurality of analyzed components corresponding to said modulated components, a total light intensity of said analyzed light beam being substantially unresponsive to said externally applied condition; filtering said analyzed light beam to provide (a) a first optical signal having only one portion of said analyzed components, said one portion including an analyzed component which varies in response to said externally applied condition, and (b) a second optical signal including said plurality of analyzed components, a sum of said plurality of analyzed components being substantially unresponsive to said externally applied condition; detecting said first and second optical signals and providing (a) a first electrical signal corresponding to a light intensity of said first optical signal, and (b) a second electrical signal corresponding to a light intensity of said second optical signal; and processing said first and second electrical signals to provide an output signal corresponding to a ratio of said first and second optical signals. - View Dependent Claims (21, 22, 23, 24, 25, 26)
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27. A method of optically sensing pressure, comprising the steps of:
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generating a broadband source light beam having a plurality of spectral components, each spectral component having a different wavelength; transmitting, with at least a first fiber optic cable, said source light beam; polarizing the transmitted source light beam to provide a polarized light beam having said plurality of spectral components; retarding said polarized light beam to provide a retarded light beam having a plurality of retarded components corresponding to said plurality of spectral components, each said retarded component having a different wavelength; detecting, with a photoelastic transducer, said pressure; modulating, with said transducer, said retarded light beam to provide a modulated light beam having a plurality of modulated components corresponding to said plurality of retarded components; analyzing said modulated light beam to provide an analyzed light beam having a plurality of analyzed components corresponding to said plurality of modulated components, said analyzed light beam having a total light intensity which remains substantially unresponsive to variations in said pressure; transmitting, with at least a second fiber optic cable, said analyzed light beam; splitting the transmitted analyzed light beam into first and second portions, each portion having said plurality of analyzed components, said second portion comprising a first optical signal; filtering said first portion to pass only one portion of said analyzed components while substantially blocking remaining analyzed components, said one portion being responsive to variations in said pressure and comprising a second optical signal; detecting, with a first photodetector, said first optical signal and providing a first electrical signal corresponding thereto; detecting, with a second photodetector, said second optical signal and providing a second electrical signal corresponding thereto; and processing said first and second electrical signals to provide an output signal corresponding to a ratio of said first and second electrical signals.
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Specification