Optical fiber sensors
First Claim
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1. A distributed optical fiber sensor cable comprising:
- a single mode optical fiber;
a plurality of means to provide spatially periodic mechanical deformation of respective portions of the fiber at spaced apart positions along its length, which portions and means define sensing elements;
the mechanical deformation providing means being such as to deform the fiber portions in response to an external perturbation to be sensed;
which fiber includes a core with cladding thereon and is able to support optical power in a mode of propagation guided in the core and in at least one unguided mode in the cladding;
each sensing element being such that, upon mechanical deformation of the respective fiber portion, resonant coupling of optical power between the mode guided by the core and the at least one unguided mode is achieved thereat;
the external perturbation serving to cause a spatially periodic mechanical deformation of the respective fiber portion along its length with a spatial period which matches the beat length between the guided and unguided modes at a respective optical wavelength;
the extent of the coupling being determined by the magnitude of the external perturbation; and
resonant coupling at each sensing element being achieved at a respective optical wavelength whereby the sensing elements can be spatially resolved along the length of the cable.
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Abstract
A distributed optical fiber sensor cable, for sensing perturbations such as pressure, comprises a length of optical fiber (10) and means adapted, in response to the perturbation to be sensed, to mechanically deform separate portions of the length of the fiber at sensing elements (11,12,13) periodically along their length in order to cause optical power launched into a mode of propagation in the core (14) and guided thereby to be coupled to an unguided mode, for example a cladding (15) mode. The coupling is optical wavelength selective and the separate sensing elements are each addressed with a different wavelength (λ11, λ12, λ13) for spatial resolution along the length of the cable.
27 Citations
10 Claims
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1. A distributed optical fiber sensor cable comprising:
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a single mode optical fiber; a plurality of means to provide spatially periodic mechanical deformation of respective portions of the fiber at spaced apart positions along its length, which portions and means define sensing elements; the mechanical deformation providing means being such as to deform the fiber portions in response to an external perturbation to be sensed; which fiber includes a core with cladding thereon and is able to support optical power in a mode of propagation guided in the core and in at least one unguided mode in the cladding; each sensing element being such that, upon mechanical deformation of the respective fiber portion, resonant coupling of optical power between the mode guided by the core and the at least one unguided mode is achieved thereat; the external perturbation serving to cause a spatially periodic mechanical deformation of the respective fiber portion along its length with a spatial period which matches the beat length between the guided and unguided modes at a respective optical wavelength; the extent of the coupling being determined by the magnitude of the external perturbation; and resonant coupling at each sensing element being achieved at a respective optical wavelength whereby the sensing elements can be spatially resolved along the length of the cable. - View Dependent Claims (2, 3, 4, 5)
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6. A distributed optical fiber sensor comprising:
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a wideband light source means whose optical output includes a plurality of different optical wavelengths; light detector means to detect each of said plurality of different optical wavelengths; a single mode optical fiber coupling the source means to the detector means; a plurality of means to provide spatially periodic mechanical deformation of respective portions of the fiber at spaced apart positions along its length, which portions and means define sensing elements; the mechanical deformation providing means being such as to deform the fiber portions in response to an external perturbation to be sensed; which fiber includes a core with cladding thereon and is able to support optical power in a mode of propagation guided in the core and in at least one unguided mode in the cladding; each sensing element being such that, upon mechanical deformation of the respective fiber portion, resonant coupling of optical power between the mode guided by the core and the at least one unguided mode is achieved thereat; the external perturbation serving at a said sensing element to cause a spatially periodic mechanical deformation of the respective fiber portion along its length with a spatial period which mathces the beat length between the guided and unguided modes at a respective one of said plurality of different optical wavelengths; the extent of the coupling being determined by the magnitude of the external perturbation; and resonant coupling at each sensing element being achieved at a respective one of said plurality of different optical wavelengths whereby the sensing elements can be spatially resolved along the length of the fiber. - View Dependent Claims (7, 8, 9, 10)
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Specification
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Current AssigneeSTC PLC (f/k/a Standard Telephones and Cables)
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Original AssigneeSTC PLC (f/k/a Standard Telephones and Cables)
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InventorsBrambley, Roger J., Epworth, Richard E.
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Primary Examiner(s)LEE, JOHN D
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Application NumberUS07/059,239Time in Patent Office363 DaysField of Search350/96.15, 350/96.19, 350/96.29, 250/227US Class Current385/13CPC Class CodesG01D 5/35383 using multiple sensor devic...
