Fiber optic strain sensor and read-out system
First Claim
1. An optical sensor, comprising:
- a first single mode optical fiber having a predetermined length of a graded-index multimode first optical fiber attached to an end thereof, said first optical fiber having an unattached end;
a first reflective member, said first reflective member being spaced by a gap from said first unattached end of said first optical fiber, said first reflective member comprising a second unattached end of a graded-index multimode second optical fiber, an attached end of which is attached to an end of a second single-mode optical fiber;
whereinsaid predetermined lengths of graded-index first and second optical fiber are fused to said first and second single mode optical fibers, respectively.
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Abstract
An optical sensor is described comprising a first optical fiber and a first reflective member. The first optical fiber has a first predetermined length of graded-index multimode optical fiber attached to its end. The first reflective member and the first optical fiber are arranged such that a gap is formed between the unattached end of the graded-index multimode optical fiber and the first reflective member. Also described is a rugged sensor design incorporating the first optical fiber and first reflective sensor as well as a method for providing the predetermined length of graded-index multimode fiber at the end of the first optical fiber. Finally, a readout system for an optical sensor is also described which comprises two optical paths differing in length by an amount equal to an optical path distance in the optical sensor. The readout system also comprises an optical source having a wavelength differing from that of the optical sensor, a modulator and a controller. The readout system provides a linear output signal that is independent of temperature and vibration effects associated with the read-out system.
88 Citations
27 Claims
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1. An optical sensor, comprising:
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a first single mode optical fiber having a predetermined length of a graded-index multimode first optical fiber attached to an end thereof, said first optical fiber having an unattached end; a first reflective member, said first reflective member being spaced by a gap from said first unattached end of said first optical fiber, said first reflective member comprising a second unattached end of a graded-index multimode second optical fiber, an attached end of which is attached to an end of a second single-mode optical fiber;
whereinsaid predetermined lengths of graded-index first and second optical fiber are fused to said first and second single mode optical fibers, respectively. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An optical sensor with read-out system comprising:
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an optical sensor comprising first and second optical paths differing in length by a predetermined distance, said optical sensor providing an optical signal output at a first wavelength responsive to an environment sensed by said optical sensor; an optical source for generating an optical source output at a second wavelength differing from said first wavelength; third and fourth optical paths differing in length by a distance substantially equal to said predetermined distance, said optical signal output and said optical source output coupled to said third and fourth optical paths such that a first portion of said optical signal output and a first portion of said optical source output comprise a first optical beam traversing said third optical path and such that a second portion of said optical signal output and a second portion of said optical source output comprise a second optical beam traversing said fourth optical path; a modulator for modulating the phase of at least one of said first and second optical beams; and a controller for sensing a first change in phase relationship between said first and second optical beams at said first wavelength, for sensing a second change in phase relationship between said first and second optical beams at said second wavelength, and for providing a signal to said modulator based on a difference between said first and second changes in phase relationship, said controller returning said phase relationship between said first and second optical beams to a predetermined phase relationship independent of temperature and vibration effects in said read-out system. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15)
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16. A method for linearizing an optical signal output at a first wavelength responsive to an environment sensed by an optical sensor comprising first and second optical paths differing in length by a predetermined distance, said method comprising the steps of:
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coupling said optical signal output of said optical sensor at said first wavelength and an optical source output from an optical source operating at a second wavelength different from said first wavelength to third and fourth optical paths such that a first portion of said optical signal output and a first portion of said optical source output comprise a first optical beam traversing said third optical path and such that a second portion of said optical signal output and a second portion of said optical source output comprise a second optical beam traversing said fourth optical path, said third and fourth optical paths differing in length by a distance substantially equal to said predetermined distance; sensing a first change in phase relationship between said first and second optical beams at said first wavelength and a second change in phase relationship between said first and second optical beams at said second wavelength; and modulating the phase of at least one of said first and second optical beams based on a difference between said first and second changes in phase relationship to return said phase relationship between said first and second optical beams to a predetermined phase relationship independent of temperature and vibration effects in said read-out system. - View Dependent Claims (17, 18, 19)
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20. An optical sensor read-out system for use in connection with an optical sensor comprising first and second optical paths differing in length by a predetermined distance for providing an optical signal output at a first wavelength responsive to an environment sensed by said optical sensor, said optical sensor read-out system comprising:
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an optical source for generating an optical source output at a second wavelength differing from said first wavelength; third and fourth optical paths differing in length by a distance substantially equal to said predetermined distance, said optical signal output and said optical source output coupled to said third and fourth optical paths such that a first portion of said optical signal output and a first portion of said optical source output comprise a first optical beam traversing said third optical path and such that a second portion of said optical signal output and a second portion of said optical source output comprise a second optical beam traversing said fourth optical path; a modulator for modulating the phase of at least one of said first and second optical beams; and a controller for sensing a first change in phase relationship between said first and second optical beams at said first wavelength, for sensing a second change in phase relationship between said first and second optical beams at said second wavelength, and for providing a signal to said modulator based on a difference between said first and second changes in phase relationship, said controller returning said phase relationship between said first and second optical beams to a predetermined phase relationship independent of temperature and vibration effects in said read-out system. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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Specification