US5488475A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Active fiber cavity strain sensor with temperature independence
Assignee: United States Department of the Navy
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Filing: 1994-03-31
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Granted: 1996-01-30
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Expires: 2014-03-31
Abstract
Abstract A strain sensor system formed from a laser cavity where changes in length of the cavity are used to measure strain. The cavity can include a passive optical fiber strain sensing section and/or an active doped optical fiber section that lases when pumped by a laser pump. The cavity can be a ring or linear cavity with or without mode locking. The light oscillating in the cavity sets up multiple oscillation modes. The multiple modes create beat modes or frequencies. The measured frequency difference between beat mode frequencies is inversely proportional to the length of the cavity. The measured frequency change in one of the mode frequencies or one of the beat frequencies is proportional to the absolute strain on the fiber. A heavy metal fluoride glass sensing section makes the sensor temperature insensitive.
Inventors
- 👤 Edward J. Friebele
- 👤 Alan D. Kersey
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-08 12:39
CPC Classifications
G; G01; G01B; G01B11/00; G01B11/16; G01B11/18; G01D; G01D5/00; G01D5/26; G01D5/32; G01D5/34; G01D5/353; G01D5/35338; G01D5/35341; G01D5/35348; G01D5/3537; G01D5/3538
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
70 words
A strain sensor, comprising: a laser pump; an active doped fiber gain section coupled to and pumped to a lasing state by the said pump; and a measurement device coupled to said gain section and measuring strain responsive to an oscillation frequency of light exiting from said gain section; wherein said measurement device comprises a beat frequency measurement device measuring a beat frequency of two oscillation modes of said section.
Claim 2
Dependent Claim
70 words
A strain sensor, comprising: a laser pump; an active doped fiber gain section coupled to and pumped to a lasing state by the said pump; and a measurement device coupled to said gain section and measuring strain responsive to an oscillation frequency of light exiting from said gain section; wherein said measurement device comprises a beat frequency measurement device measuring a beat frequency of two oscillation modes of said section.
Claim 3
Dependent Claim
15 words
A sensor as recited in claim 1, wherein said gain section forms a ring cavity.
Claim 4
Dependent Claim
18 words
A sensor as recited in claim 2, wherein said strain sensing section comprises a mode locked fiber ring.
Claim 5
Dependent Claim
15 words
A sensor as recited in claim 1, wherein said gain section forms a linear cavity.
Claim 6
Dependent Claim
33 words
A sensor as recited in claim 1, wherein said gain section comprises: a Bragg grating coupled to said pump; an Er-doped fiber coupled to said grating; and a mirror coupled to said fiber.
Claim 7
Dependent Claim
17 words
A sensor as recited in claim 1, wherein said gain section comprises an Er-doped optical fiber ring.
Claim 8
Dependent Claim
20 words
A sensor as recited in claim 1, wherein said gain section comprises an athermal, heavy metal glass fluoride, optical fiber.
Claim 9
Dependent Claim
33 words
A sensor as recited in claim 1, further comprising a fiber strain sensing section coupled to said gain section and wherein said measurement device measures oscillation in said strain sensing and gain sections.
Claim 10
Dependent Claim
26 words
A sensor as recited in claim 8, wherein said measurement device measures a beat frequency of two oscillation modes in said strain sensing and gain sections.
Claim 11
Dependent Claim
18 words
A sensor as recited in claim 8, wherein said strain sensing and gain sections form a ring cavity.
Claim 12
Dependent Claim
18 words
A sensor as recited in claim 8, wherein said strain sensing and gain sections form a linear cavity.
Claim 13
Dependent Claim
83 words
A strain sensor, comprising: a laser pump; a ring laser cavity coupled to said pump, said cavity comprising: a wavelength division multiplexer coupler coupled to said pump; an Er-doped, athermal, heavy metal glass, optical fiber coupled to said multiplexer coupler; a 3 dB output coupler coupled to said Er-doped fiber; and a strain sensing, athermal, heavy metal fluoride glass, optical fiber coupled between said multiplexer and 3 dB couplers; and a multi-mode beat frequency measurement device coupled to said 3 dB output coupler.
Claim 14
Dependent Claim
83 words
A strain sensor, comprising: a laser pump; a ring laser cavity coupled to said pump, said cavity comprising: a wavelength division multiplexer coupler coupled to said pump; an Er-doped, athermal, heavy metal glass, optical fiber coupled to said multiplexer coupler; a 3 dB output coupler coupled to said Er-doped fiber; and a strain sensing, athermal, heavy metal fluoride glass, optical fiber coupled between said multiplexer and 3 dB couplers; and a multi-mode beat frequency measurement device coupled to said 3 dB output coupler.
Claim 15
Dependent Claim
77 words
A fiber optic sensor, comprising: a fiber optic laser cavity; means for pumping said cavity; and a fiber optic gain portion; wherein said cavity, said means for pumping, and said gain portion are operatively interconnected to produce a plurality of laser beat frequencies in said cavity; and wherein said sensor further comprises means for detecting frequency change, induced by mechanical straining of at least a portion of said cavity, of a preselected one of said beat frequencies.
Claim 16
Dependent Claim
77 words
A fiber optic sensor, comprising: a fiber optic laser cavity; means for pumping said cavity; and a fiber optic gain portion; wherein said cavity, said means for pumping, and said gain portion are operatively interconnected to produce a plurality of laser beat frequencies in said cavity; and wherein said sensor further comprises means for detecting frequency change, induced by mechanical straining of at least a portion of said cavity, of a preselected one of said beat frequencies.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1999-01-29 | 1999-07-31 | 2000-01-30 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2003-01-29 | 2003-07-31 | 2004-01-30 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2007-01-29 | 2007-07-31 | 2008-01-30 | $7700.00 | Window Closed / Lapsed |