US4749246A
Expired / Lapsed
US
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Optical fiber sensors
Assignee: STC PLC
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Filing: 1987-06-10
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Granted: 1988-06-07
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Expires: 2007-06-10
Abstract
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 (λ 11 , λ 12 , λ 13 ) for spatial resolution along the length of the cable.
Inventors
- 👤 Richard E. Epworth
- 👤 Roger J. Brambley
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 21:31
CPC Classifications
G; G01; G01D; G01D5/00; G01D5/26; G01D5/32; G01D5/34; G01D5/353; G01D5/35383
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
215 words
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.
Claim 2
Dependent Claim
215 words
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.
Claim 3
Dependent Claim
37 words
A sensor cable as claimed in claim 1, wherein each deformation providing means comprises a machined grating which serves to mechanically deform the respective portion of the fiber in response to an external perturbation to be sensed.
Claim 4
Dependent Claim
22 words
A sensor cable as claimed in claim 2, wherein the deformation providing means of the different sensing elements differ from one another.
Claim 5
Dependent Claim
42 words
A sensor cable as claimed in claim 1, wherein in use of the cable the extent of the power loss in the mode guided by the core, after coupling to the at least one unguided mode, provides a measure of the perturbation.
Claim 6
Dependent Claim
39 words
A sensor cable as claimed in claim 1, wherein in use of the cable the extent of the power induced in the at least one unguided mode, after coupling from the guided mode, comprises a measure of the perturbation.
Claim 7
Dependent Claim
267 words
A distributed optical fiber sensor comprising: 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.
Claim 8
Dependent Claim
267 words
A distributed optical fiber sensor comprising: 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.
Claim 9
Dependent Claim
37 words
A sensor as claimed in claim 6, wherein in use the extent of power loss in the mode guided by the core, after coupling to the at least one unguided mode, provides a measure of the perturbation.
Claim 10
Dependent Claim
35 words
A sensor as claimed in claim 6, wherein in use the extent of the power induced in the at least one unguided mode, after coupling from the guided mode, comprises a measure of the perturbation.
Claim 11
Dependent Claim
36 words
A sensor as claimed in claim 6, wherein each deformation providing means comprises a machined grating which serves to mechanically deform the respective portion of the fiber in response to an external perturbation to be sensed.
Claim 12
Dependent Claim
21 words
A sensor as claimed in claim 9, wherein the deformation providing means of the different sensing elements differ from one another.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1991-06-07 | 1991-12-07 | 1992-06-07 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1995-06-07 | 1995-12-07 | 1996-06-07 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1999-06-07 | 1999-12-07 | 2000-06-07 | $7700.00 | Window Closed / Lapsed |