Patent US949869A successfully refreshed from Google Patents.
US4530603A
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US
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Stabilized fiber optic sensor
Assignee: Leland Stanford Junior University
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Filing: 1982-09-29
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Granted: 1985-07-23
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Expires: 2002-09-29
Abstract
Abstract A fiber optic sensor comprises a length of optical fiber, forming a loop, and a fiber optic directional coupler for optically closing the loop. The loop and coupler form a resonant cavity for light circulating therethrough. A PZT cylinder, about which the fiber loop is wrapped, is utilized to control the total round trip phase delay of the circulating light, and thus, control the intensity of the optical output signal. The phase delay is adjusted to a point where the optical output signal is at maximum sensitivity to changes in phase. When the fiber loop is exposed to, e.g., acoustic waves, the loop length changes correspondingly, thereby causing the phase delay, and thus, the optical output signal to vary. By detecting variations in output signal intensity, the frequency and intensity of the acoustic waves may be determined. The sensor also includes a feedback system for stabilizing the fiber loop against low frequency thermal drift.
Inventors
- 👤 Herbert J. Shaw
- 👤 Marvin Chodorow
- 👤 Loren F. Stokes
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 22:46
CPC Classifications
G; G02; G02B; G02B6/00; G02B6/24; G02B6/26; G01; G01H; G01H9/00; G01H9/004; G02B26/00; G02B26/06; G02F; G02F1/00; G02F1/01; G02F1/0128; G02F1/0131; G02F1/0134
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
177 words
A fiber optic sensor, comprising: a single uninterrupted strand of optical fiber having first and second end portions and a loop portion therebetween; fiber optic coupling means for optically closing said fiber loop; means for applying a lightwave to said first end portion for propagation through said fiber to said second end portion to provide an optical output signal, the intensity of said optical output signal dependent upon the length of said loop; means for controlling the roundtrip phase delay of light circulating through said fiber loop to provide a resonant cavity for said circulating light; said fiber loop length sensitive to first and second ambient effects, said first ambient effect varying in a first frequency range, said second ambient effect varying in a second frequency range; means for compensating for fiber loop length changes caused by said first ambient effect to stabilize said output signal against said first ambient effect, said output signal remaining sensitive to said second ambient effect; and means for detecting intensity variations in said output signal to detect said second ambient effect.
Claim 2
Dependent Claim
177 words
A fiber optic sensor, comprising: a single uninterrupted strand of optical fiber having first and second end portions and a loop portion therebetween; fiber optic coupling means for optically closing said fiber loop; means for applying a lightwave to said first end portion for propagation through said fiber to said second end portion to provide an optical output signal, the intensity of said optical output signal dependent upon the length of said loop; means for controlling the roundtrip phase delay of light circulating through said fiber loop to provide a resonant cavity for said circulating light; said fiber loop length sensitive to first and second ambient effects, said first ambient effect varying in a first frequency range, said second ambient effect varying in a second frequency range; means for compensating for fiber loop length changes caused by said first ambient effect to stabilize said output signal against said first ambient effect, said output signal remaining sensitive to said second ambient effect; and means for detecting intensity variations in said output signal to detect said second ambient effect.
Claim 3
Dependent Claim
46 words
A fiber optic sensor, as defined in claim 1, wherein said phase delay controlling means provide a total roundtrip phase delay for said circulating light equal to an integral number of wavelengths ±φ 0 , where: ##EQU13## and where K r is the resonant coupling constant.
Claim 4
Dependent Claim
42 words
A fiber optic sensor, as defined in claim 2, wherein said phase delay controlling means provides a total roundtrip phase delay for said circulating light such that the sensitivity of said output signal to changes in loop length is at a maximum.
Claim 5
Dependent Claim
16 words
A fiber optic sensor, as defined in claim 1, wherein said first ambient effect is thermal.
Claim 6
Dependent Claim
18 words
A fiber optic sensor, as defined in claim 1, wherein said second ambient effect comprises an acoustic wave.
Claim 7
Dependent Claim
27 words
A fiber optic sensor, as defined in claim 1, wherein said compensating means comprises: a PZT cylinder, about which a portion of said fiber loop is wrapped.
Claim 8
Dependent Claim
53 words
A fiber optic sensor, as defined in claim 6, wherein said compensating means additionally comprises: means for driving said PZT cylinder with a signal from said detecting means, said driving means filtering said signal to pass frequency components in said first frequency range, while effectively blocking frequency components in said second frequency range.
Claim 9
Dependent Claim
29 words
A fiber optic sensor, as defined in claim 7, wherein said driving means comprises an integrator which provides a preferential gain for signal components in said first frequency range.
Claim 10
Dependent Claim
27 words
A fiber optic sensor, as defined in claim 1, wherein said controlling means comprises a PZT cylinder about which a portion of said fiber loop is wrapped.
Claim 11
Dependent Claim
19 words
A fiber optic sensor, as defined in claim 1, wherein said coupling means comprises a fiber optic directional coupler.
Claim 12
Independent Claim
95 words
A method of sensing acoustic waves utilizing an optical fiber, said method comprising: forming a loop in said fiber; applying input light for propagation through said loop to provide an optical output signal; using a fiber optic coupler to optically close said loop; selecting the length of said loop to provide a resonant cavity, said loop length affecting the intensity of said output signal; compensating for thermally induced loop length changes to stabilize said output signal intensity against said thermally induced changes; and detecting said output signal to sense the presence of said acoustic waves.
Claim 13
Independent Claim
95 words
A method of sensing acoustic waves utilizing an optical fiber, said method comprising: forming a loop in said fiber; applying input light for propagation through said loop to provide an optical output signal; using a fiber optic coupler to optically close said loop; selecting the length of said loop to provide a resonant cavity, said loop length affecting the intensity of said output signal; compensating for thermally induced loop length changes to stabilize said output signal intensity against said thermally induced changes; and detecting said output signal to sense the presence of said acoustic waves.
Claim 14
Dependent Claim
52 words
A method of sensing acoustic waves utilizing an optical fiber, as defined in claim 11, wherein said selecting step comprises: determining the point of maximum sensitivity of said output signal intensity to loop length changes; and selecting said loop length to provide an output signal intensity at said point of maximum sensitivity.
Claim 15
Dependent Claim
50 words
A method of sensing acoustic waves utilizing an optical fiber, as defined in claim 11, wherein said compensating step comprises: detecting components of said output signal having a frequency below that of said sensed acoustic waves; and varying the length of said loop in response to said detected frequency components.
Claim 16
Independent Claim
168 words
A method of sensing an ambient effect utilizing an optical fiber, having first and second end portions, said method comprising: forming a loop in said fiber, between said first and second end portions; optically closing said loop to provide a resonant cavity for light circulating in said loop; applying input light to said first end portion, for propagation through said fiber loop to provide an optical output signal at said second end portion, said output signal sensitive to the total roundtrip phase delay of light circulating in said fiber loop; controlling the roundtrip phase delay of light circulating through said fiber loop to adjust said optical output signal to a selected value, between a minimum value, corresponding to full resonance of said light circulating in said loop, and a maximum value corresponding to non-resonance of said light circulating in said loop; exposing said loop to said ambient effect to cause variations in said roundtrip phase delay; and detecting said ambient effect by observing variations from said selected value.
Claim 17
Independent Claim
168 words
A method of sensing an ambient effect utilizing an optical fiber, having first and second end portions, said method comprising: forming a loop in said fiber, between said first and second end portions; optically closing said loop to provide a resonant cavity for light circulating in said loop; applying input light to said first end portion, for propagation through said fiber loop to provide an optical output signal at said second end portion, said output signal sensitive to the total roundtrip phase delay of light circulating in said fiber loop; controlling the roundtrip phase delay of light circulating through said fiber loop to adjust said optical output signal to a selected value, between a minimum value, corresponding to full resonance of said light circulating in said loop, and a maximum value corresponding to non-resonance of said light circulating in said loop; exposing said loop to said ambient effect to cause variations in said roundtrip phase delay; and detecting said ambient effect by observing variations from said selected value.
Claim 18
Dependent Claim
43 words
A method of sensing an ambient effect utilizing an optical fiber having first and second end portions, as defined in claim 14, wherein said selected value corresponds to a point of maximum sensitivity of said optical output signal to said roundtrip phase delay.
Claim 19
Dependent Claim
39 words
A method of sensing an ambient effect utilizing an optical fiber having first and second end portions, as defined in claim 14, wherein said variations in said output signal are substantially proportional to said variations in said phase delay.
Claim 20
Dependent Claim
30 words
A method of sensing an ambient effect utilizing an optical fiber having first and second end portions, as defined in claim 14, wherein said ambient effect is an acoustic wave.
Claim 21
Dependent Claim
128 words
A fiber optic sensor for sensing an ambient effect, comprising: an optical fiber having first and second end portions and a loop portion therebetween; means for optically closing said loop to provide a resonant cavity; means for applying a lightwave to said first end portion for propagation through said loop to said second end portion to provide an optical output signal; means for controlling the total roundtrip phase delay for light in said loop to adjust said output signal to a selected value, between a minimum value, corresponding to full resonance of said lightwave in said loop, and a maximum value, corresponding to nonresonance of said lightwave in said loop; and means for detecting variations in said output signal from said selected value to sense said ambient effect.
Claim 22
Dependent Claim
128 words
A fiber optic sensor for sensing an ambient effect, comprising: an optical fiber having first and second end portions and a loop portion therebetween; means for optically closing said loop to provide a resonant cavity; means for applying a lightwave to said first end portion for propagation through said loop to said second end portion to provide an optical output signal; means for controlling the total roundtrip phase delay for light in said loop to adjust said output signal to a selected value, between a minimum value, corresponding to full resonance of said lightwave in said loop, and a maximum value, corresponding to nonresonance of said lightwave in said loop; and means for detecting variations in said output signal from said selected value to sense said ambient effect.
Claim 23
Dependent Claim
38 words
A fiber optic sensor, as defined in claim 18, wherein said output signal is sensitive to said phase delay, and said selected value corresponds to a point of maximum sensitivity of said output signal to said phase delay.
Claim 24
Dependent Claim
17 words
A fiber optic sensor, as defined in claim 18, wherein said ambient effect is an acoustic wave.
Claim 25
Dependent Claim
19 words
A fiber optic sensor, as defined in claim 18, wherein said optically closing means comprises a fiber optic coupler.
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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) | 1988-07-22 | 1989-01-21 | 1989-07-23 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-07-22 | 1993-01-21 | 1993-07-23 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-07-22 | 1997-01-21 | 1997-07-23 | $7700.00 | Window Closed / Lapsed |