EP0104943A2
Expired / Lapsed
EP
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Stabilized fiber optic sensor
Assignee: Leland Stanford Junior University
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Filing: 1983-09-27
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Granted: —
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Expires: 2003-09-27
Abstract
Abstract A fiber optic sensor comprises a length of optical fiber (10), forming a loop (40), and a fiber optic directional coupler (20) for optically closing the loop (14). The loop (14) and coupler (20) form a resonant cavity for light circulating therethrough. A PZT cylinder (118), about which the fiber loop (14) 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 W o . The phase delay is adjusted to a point Z where the optical output signal W e is at maximum sensitivity to changes in phase. When the fiber loop (14) is exposed to, e.g., acoustic waves, the loop length changes correspondingly, thereby causing the phase delay, and thus, the optical output signal W o 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 (14) against low frequency thermal drift.
Inventors
- 👤 Herbert John Shaw
- 👤 Marvin Chodorow (Nmi)
- 👤 Loren F. Stokes
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 20:01
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: 13
Claim 1
Independent Claim
218 words
A fiber optic sensor, comprising: a single uninterrputed strand (10) of optical fiber having first and second end portions (12,16) and a loop portion (14) therebetween; a fiber optic coupler (20) for optically closing said fiber loop (14); a light source (22) for applying a lightwave W i to said first end portion (12) for propagation through said fiber (10) to said second end portion (16) to provide an optical output signal, W o the intensity of said optical output signal W o dependent upon the length of said loop (14); a phase delay device (118) for controlling the roundtrip phase delay of light circulating through said fiber loop (14) 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; a stabilization device (114) for driving said phase delay device (118) to compensate for fiber loop length changes caused by said first ambient effect to stabilize said output signal W o against said first ambient effect, said output signal W o remaining sensitive to said second ambient effect; and a detector (110) for detecting intensity variations in said output signal W o to detect said second ambient effect.
Claim 2
Dependent Claim
218 words
A fiber optic sensor, comprising: a single uninterrputed strand (10) of optical fiber having first and second end portions (12,16) and a loop portion (14) therebetween; a fiber optic coupler (20) for optically closing said fiber loop (14); a light source (22) for applying a lightwave W i to said first end portion (12) for propagation through said fiber (10) to said second end portion (16) to provide an optical output signal, W o the intensity of said optical output signal W o dependent upon the length of said loop (14); a phase delay device (118) for controlling the roundtrip phase delay of light circulating through said fiber loop (14) 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; a stabilization device (114) for driving said phase delay device (118) to compensate for fiber loop length changes caused by said first ambient effect to stabilize said output signal W o against said first ambient effect, said output signal W o remaining sensitive to said second ambient effect; and a detector (110) for detecting intensity variations in said output signal W o 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 device (118) provides a total roundtrip phase delay for said circulating light equal to an integral number of wavelengths +φ 0 , where: and and where K r is the resonant coupling constant.
Claim 4
Dependent Claim
48 words
A fiber optic sensor, as defined in either of Claims 1 or 2, wherein said phase delay device (118) provides a total roundtrip phase delay for said circulating light such that the sensitivity of said output signal W o to changes in loop length is at a maximum.
Claim 5
Dependent Claim
20 words
A fiber optic sensor, as defined in any of Claims 1 to 3, wherein said first ambient effect is thermal.
Claim 6
Dependent Claim
22 words
A fiber optic sensor, as defined in any of Claims 1 to 4, wherein said second ambient effect comprises an acoustic wave.
Claim 7
Dependent Claim
34 words
A fiber optic sensor, as defined in any of Claims 1 to 5, wherein said phase delay device comprises: a PZT cylinder (118), about which a portion of said fiber loop 14 is wrapped.
Claim 8
Dependent Claim
59 words
A fiber optic sensor, as defined in any of Claims 1 to 6, wherein said stablization device (114) comprises: electronics (114) for driving said phase delay device with an electrical signal from said detector 110, said electronics 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
28 words
A fiber optic sensor, as defined in Claim 7, wherein said electronics comprises an integrator which provides a preferential gain for signal components in said first frequency range.
Claim 10
Independent Claim
114 words
A method of sensing acoustic waves utilizing an optical fiber, said method comprising: forming a loop (14) in an optical fiber (10); applying input light for propagation through said loop (14) to provide an optical output signal W o ; using a fiber optic coupler (20) to optically close said loop (14); selecting the length of said loop (14) to provide a resonant cavity, said loop length affecting the intensity of said output signal W o ; compensating for thermally induced loop length changes to stabilize the intensity of said output signal W o against said thermally induced changes; and detecting said output signal W o to sense the presence of said acoustic waves.
Claim 11
Independent Claim
114 words
A method of sensing acoustic waves utilizing an optical fiber, said method comprising: forming a loop (14) in an optical fiber (10); applying input light for propagation through said loop (14) to provide an optical output signal W o ; using a fiber optic coupler (20) to optically close said loop (14); selecting the length of said loop (14) to provide a resonant cavity, said loop length affecting the intensity of said output signal W o ; compensating for thermally induced loop length changes to stabilize the intensity of said output signal W o against said thermally induced changes; and detecting said output signal W o to sense the presence of said acoustic waves.
Claim 12
Dependent Claim
56 words
A method of sensing acoustic waves utilizing an optical fiber, as defined in Claim 9, wherein said selecting step comprises: determining the point of maximum sensitivity of the intensity of said output signal W o to loop length changes; and selecting said loop length to provide an output signal intensity at said point of maximum sensitivity.
Claim 13
Independent Claim
57 words
A method of sensing acoustic waves utilizing an optical fiber, as defined in either of Claims 9 or 10, wherein said compensating step comprises: detecting components of said output signal W o having a frequency below that of said sensed acoustic waves; and varying the length of said loop (14) in response to said detected frequency components.
References Cited (Backward Citations)
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