Fiber optic sensors operating at DC
First Claim
1. A physical sensor for detecting a physical quantity varying at any rate below a maximum rate with minimal disturbance from environmentally induced perturbations, comprising:
- a first highly birefringent optical fiber having orthogonal fast and slow axes, a first coherent light signal passing through said first fiber;
a second highly birefringent optical fiber having orthogonal fast and slow axes, a second coherent light signal passing through said second fiber, said first and second fibers being equally birefringent, said second fiber being positioned longitudinally adjacent to said first fiber, said fast axis of said first fiber being orthogonal to said fast axis of said second fiber;
coupling means mechanically coupled to said first and second fibers for asymmetrically altering the birefringence of said first and second fibers in response to said physical quantity and for rotating the states of polarization of said first and second light signals in the same direction in response to said physical quantity, said birefringence of said first and second fibers being symmetrically altered in response to environmental perturbations such that the states of polarization of said first and second light signals are rotated in opposite directions in response to said environmental perturbations; and
detection means for detecting the states of polarization of said first and second light signals, for combining said detected states of polarization altered due to said physical quantity, for cancelling said detected states of polarization altered due to said environmental perturbations, and for producing an output signal representative of said physical quantity.
1 Assignment
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Accused Products
Abstract
A fiber optic sensor for detecting and/or measuring a physical quantity varying at any frequency from a maximum desired frequency down to zero frequency with minimum disturbance from environmentally induced perturbations. A first highly birefringent optical fiber is positioned longitudinally adjacent to a second equally birefringent fiber. Each fiber has orthogonally disposed fast and slow axes. The fibers are oriented such that their fast axes are perpendicular to each other. When subjected to stress caused by a physical quantity acting on the fibers through a transducer, the birefringence of each of the two fibers is asymmetrical altered thereby rotating the states of polarization of coherent light signals passing through the two fibers in a common direction. Environmental perturbations symmetrically alter the birefringence of each of the fibers thereby rotating the states of polarization of the light signals in opposite directions. The states of polarization of the light signals emanating from the two fibers are detected and combined such that the changes due to the physical quantity enhance each other while the changes due to environmental perturbations are cancelled.
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Citations
25 Claims
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1. A physical sensor for detecting a physical quantity varying at any rate below a maximum rate with minimal disturbance from environmentally induced perturbations, comprising:
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a first highly birefringent optical fiber having orthogonal fast and slow axes, a first coherent light signal passing through said first fiber; a second highly birefringent optical fiber having orthogonal fast and slow axes, a second coherent light signal passing through said second fiber, said first and second fibers being equally birefringent, said second fiber being positioned longitudinally adjacent to said first fiber, said fast axis of said first fiber being orthogonal to said fast axis of said second fiber; coupling means mechanically coupled to said first and second fibers for asymmetrically altering the birefringence of said first and second fibers in response to said physical quantity and for rotating the states of polarization of said first and second light signals in the same direction in response to said physical quantity, said birefringence of said first and second fibers being symmetrically altered in response to environmental perturbations such that the states of polarization of said first and second light signals are rotated in opposite directions in response to said environmental perturbations; and detection means for detecting the states of polarization of said first and second light signals, for combining said detected states of polarization altered due to said physical quantity, for cancelling said detected states of polarization altered due to said environmental perturbations, and for producing an output signal representative of said physical quantity. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 18)
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15. A physical sensor for detecting a physical quantity varying at any rate below a maximum rate with minimum disturbance from environmentally induced perturbations, comprising:
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source means for suppling a first coherent light signal and a second coherent light signal, said first and second light signals being lineraly polarized; a first highly birefringent optical fiber having orthogonal fast and slow axes, said first light signal being launched into an input end of said first fiber, said first light signal being oriented with respect to said first fiber such that it is linearly polarized at an angle of 45 degrees to each of the fast and slow axes of said first fiber; a second highly birefringent optical fiber having orthogonal fast and slow axes, said first and second fibers being equally birefringent, said second fiber being positioned longitudinally adjacent to said first fiber, said fast axis of said first fiber being orthogonal to said fast axis of said second fiber, said second light signal being launched into an input end of said second fiber, said second light signal being oriented with respect to said second fiber such that it is linearly polarized at an angle of 45 degrees to each of the fast and slow axes of said second fiber; coupling means mechanically coupled to said first and second fibers for asymmetrically altering the birefringence of said first and second fibers in response to said physical quantity and for rotating the states of polarization of said first and second light signals in the same direction in response to said physical quantity, said birefringence of said first and second fibers being symmetrically altered in response to environmental perturbations such that the states of polarization of said first and second light signals are rotated in opposite directions in response to said environmental perturbations; and detection means for detecting the states of polarization of said first and second light signals, for combining said detected states of polarization altered due to said physical quantity, for cancelling said detected states of polarization altered due to said environmental perturbations, and for producing an output signal representative of said physical quantity. - View Dependent Claims (19)
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20. A method of detecting a physical quantity varying at any rate below a maximum rate with minimum disturbance from environmentally induced perturbations comprising the steps of:
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providing first and second equally highly birefringent optical fibers, each fiber having orthogonally disposed fast and slow axes; positioning said first fiber longitudinally adjacent said second fiber with the fast axis of said first fiber orthogonal to the fast axis of said second fiber; launching a first linearly polarized coherent light signal into said first fiber and launching a second linearly polarized light signal into said second fiber; allowing a physical quantity to asymmetrically stress said first and second fibers in response thereto so as to alter the birefringence of said first and second fibers, the states of polarization of said first and second light signals thereby being rotated in a common direction in response to said physical quantity, said first and second fibers being symmetrically stressed by environmental perturbations such that said states of polarization of said first and second signals are rotated in opposite directions in response to said environmental perturbations; detecting said states of polarization of said first and second signals emanating from said first and second fibers; and combining said detected states of polarization of said first and second signals such that changes in said states of polarization due to said physical quantity are enhanced while changes in said states of polarization due to said environmental perturbations are cancelled. - View Dependent Claims (21, 22, 23, 24, 25)
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Specification