EP0191589A2
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Coherent distributed sensor and method using short coherence length sources
Assignee: Leland Stanford Junior University
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Filing: 1986-02-05
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Granted: —
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Expires: 2006-02-05
Abstract
Abstract A distributed sensor system including an optical source (100) having a short coherence length for optionally continuously monitoring each sensor in the system. In one preferred embodiment, an array of fiber-optic sensors (110) are organized in a ladder configuration, with the sensors positioned in spaced relation and defining the rungs of the ladder. Light transmitted through the sensors is multiplexed onto a return arm (114) of the ladder, with sensor spacing being such that interference between light from different sensors is prevented. The multiplexed signals are received by an optical fiber receiver (118, 120) which couples the multiplexed light with an interfering optical reference signal to produce a phase difference signal representing conditions influencing selected sensors. Embodiments are disclosed for use of either pulsed or continuous wave light sources In another preferred embodiment, the sensors comprise a plurality of Mach-Zehnder interferometers (404,406) connected in series configuration by a common optical fiber (402), which provides multiplexed output signals from the sensors to a plurality of Mach-Zehnder interferometers (418, 420) comprising receivers. The optical path length differences between the arms (409, 410, 411 and 412) of each of the sensors (404, 406) are selected to prevent interference between the multiplexed sensor output signals from various sensors. The optical path lengths through the sensors (404, 406) and receivers (418, 420) are structured so that each receiver (418, 420) produces a phase difference signal relating to conditions affecting light transmission through a specific sensor (404,406). A phase and amplitude modulation technique is disclosed for providing heterodyned output signals from the dristributed sensor system.
Inventors
- 👤 Robert C. Youngquist
- 👤 Janet L. Brooks
- 👤 Kenneth A. Fesler
- 👤 Cassius C. Cutler
- 👤 Herbert John Shaw
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 04:46
CPC Classifications
G; G01; G01J; G01J9/00; G01D; G01D5/00; G01D5/26; G01D5/32; G01D5/34; G01D5/353; G01D5/35383
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
201 words
An apparatus for remotely sensing environmental effects on a pair of sensors (110a, 110b) characterized by: a light source (100); first and second light paths (102, 110, 114, 118a; and 102, 110b, 114, 118b) for said light source, said first and second paths being separate in at least one sensing region (110a, 110b) and being joined in a transmission region (114) which comprises a single, common propagation path, at least one of said first and second light paths influenced by an environmental effect in said sensing region; third and fourth light paths (106, 122a; and 106, 122b) which are substantially equal in length, respectively, to said first and second light paths (102, 110a, 114, 118a; and 102, 110b, 114, 118b), and which are optically coupled to the transmission region (114) of the first and second light paths, said third and fourth light paths not subject to the same environmental effect as said first and second light paths; and means (120a, 120b) for combining light from said first, second, third and fourth light paths, said means coherently coupling light only from light paths which substantially correspond in length to a specific one of said first and second light paths at any time.
Claim 2
Independent Claim
201 words
An apparatus for remotely sensing environmental effects on a pair of sensors (110a, 110b) characterized by: a light source (100); first and second light paths (102, 110, 114, 118a; and 102, 110b, 114, 118b) for said light source, said first and second paths being separate in at least one sensing region (110a, 110b) and being joined in a transmission region (114) which comprises a single, common propagation path, at least one of said first and second light paths influenced by an environmental effect in said sensing region; third and fourth light paths (106, 122a; and 106, 122b) which are substantially equal in length, respectively, to said first and second light paths (102, 110a, 114, 118a; and 102, 110b, 114, 118b), and which are optically coupled to the transmission region (114) of the first and second light paths, said third and fourth light paths not subject to the same environmental effect as said first and second light paths; and means (120a, 120b) for combining light from said first, second, third and fourth light paths, said means coherently coupling light only from light paths which substantially correspond in length to a specific one of said first and second light paths at any time.
Claim 3
Dependent Claim
104 words
An apparatus as defined in Claim 1 further characterized by: a first plurality of optical waveguide segments defining at least a portion of said first and second light paths; at least a second optical waveguide segment for propagating light through at least a portion of said third and fourth light paths; and a third optical waveguide segment optically coupled to one of said first plurality of optical waveguide segments and to said second optical waveguide segment so that light from said first plurality of waveguide segments is propagated to the optical connection with said second waveguide segment only through said third optical waveguide segment.
Claim 4
Dependent Claim
67 words
An apparatus as defined in Claim 2, wherein at least a portion of the second optical waveguide segment comprises a variable delay line, permitting the optical path length of said second optical waveguide segment to be . varied such that the optical path length of said second optical waveguide provides said third light path at a first time, and said fourth light path at a second time.
Claim 5
Dependent Claim
159 words
An apparatus as defined in Claim 1, further characterized by: at least first and second optical waveguide segments which are optically coupled to the light source and which define at least first and second optical signal transmission segments comprising said transmission regions and at least first and second sensor segments comprising said sensor regions, said sensor segments sensitive to environmental effects; at least one third optical waveguide segment which is optically coupled to said transmission segments of said first and second optical waveguide segments and mechanically independent of said first and second sensor segments and which defines said third and fourth light paths; and means optically connected to said combining means for producing a signal representing conditions causing variation of the light transmission characteristics in the sensor segments, said signal corresponding to the phase difference of coherently coupled light from the combining means, with said coupled light being coherent for said first and second sensor segments at different times.
Claim 6
Dependent Claim
201 words
An apparatus as defined in Claim 1, further characterized by: a first optical waveguide which is optically coupled to the light source; a second optical waveguide defining one of said transmission regions; first and second fiber-optic sensors defining said sensing regions, said sensors having light transmission characteristics that vary in response to environmental conditions, said sensors each having first and second terminals which are optically coupled in spaced relationship, respectively, to the first and second optical waveguides such that said sensors and said first and second waveguides define at least portions of said first and second light paths; and at least a third optical waveguide optically coupled in the combining means to the second optical waveguide and independent of the fiber-optic sensors, said third optical waveguide defining at least one of said third and fourth light paths of a length such that light signals traveling therein interfere coherently at any given time with light from no more than one of said first and second light paths in said combining means, thereby providing an output optical signal comprising the phase difference of the interfering light signals, wherein said output optical signal represents conditions causing variation in light transmission characteristics in said sensors.
Claim 7
Dependent Claim
86 words
An apparatus as defined in Claim 5, wherein said first and second fiber-optic sensors are spaced from each other such that the difference in path length of said first and second light paths is greater than a source coherence length of the light source; wherein said third optical waveguide defines said third and fourth light paths; and wherein the means for combining light from said first, second, third and fourth light paths, coherently couples light from only one pair of said light paths at any time.
Claim 8
Independent Claim
82 words
An apparatus as defined in-either of Claims 5 or 6, wherein at least a portion of the third optical waveguide comprises a variable delay line, permitting the optical path length of said third optical waveguide to be varied such that the optical path length of said third optical waveguide defines an optical path substantially equal to said first light path at a first time, and an optical path of a length substantially equal to said second light path at a second time.
Claim 9
Dependent Claim
87 words
An apparatus as defined in Claim 1, further characterized by: a plurality of optical fiber sensors optically coupled to the light source, each defining at least said first and second light paths such that said light paths are of different lengths; and wherein said means for combining light from said first, second, third and fourth light paths combines light signals from said optical fiber paths so that light signals which coherently couple produce a signal indicating the difference between the environmental effects detected on two different sensors.
Claim 10
Dependent Claim
130 words
An apparatus as defined in Claim 1, further characterized in that: the first, second, third and fourth light paths are optically combined to define an optical path having a sensor portion sensitive to environmental effects; the apparatus further characterized by: means for transmitting light from the light source in a first and second direction through said optical path so that said light in said first and second directions propagates through said sensor portion at different times; and wherein said means for combining light combines that light which has traveled said optical path in said first direction with light which has traveled said optical path in said second direction so that said combined light which couples coherently comprises a measure of rate of change of environmental conditions influencing said sensor portion.
Claim 11
Independent Claim
31 words
An apparatus as defined in any of Claims 1, 2, 3, 4, 5, 6, 7, 8 or 9, wherein the light source comprises an optical source having a short coherence length.
Claim 12
Independent Claim
40 words
An apparatus defined in any of Claims 1, 2, 3, 4, 5 or 8, wherein the first and second light paths are different in length by an amount at least as great as one coherence length of the light source.
Claim 13
Independent Claim
26 words
An apparatus as defined in any of Claims 1, 2, 3, 4 or 5, wherein the third and fourth light paths exist only at different times.
Claim 14
Independent Claim
52 words
An apparatus as defined in any of Claims 1, 2, 3 or 8, wherein the means for combining light provides an output signal comprising the phase difference of the coherently coupled light, said phase difference representative of environmental effects influencing that light path whose light is coherently coupled in said combining means.
Claim 15
Independent Claim
19 words
An apparatus as defined in either of Claims 8 or 9, wherein the light source produces pulsed optical signals.
Claim 16
Dependent Claim
315 words
An apparatus as defined in Claim 1, further characterized in that: said light source comprises a source of pulsed optical signals; and wherein the apparatus is further characterized by: a first optical waveguide which is optically coupled to the signal source; a second optical waveguide defining one of said transmission regions; a plurality of optical waveguide sensors defining said sensing regions, said sensors having light transmission characteristics that vary in response to environmental conditions, and said sensors having first and second terminals, each sensor being optically coupled at its first and second terminals, respectively, to the first and second optical waveguides such that said sensors and said first and second waveguides define at least portions of the first and second light paths, said sensors being located in spaced relation along the first and second optical waveguides so that portions of an optical pulse signal from the signal source are transmitted from the first waveguide through each sensor, and are then multiplexed onto the second optical waveguide, producing a string of pulse signals on said second optical waveguide, wherein coupling locations of the optical waveguide sensors on the first and second optical waveguides are spaced such that the optical path length difference for light traveling through any two adjacent sensors is substantially identical and is great enough that the pulse signals on the second waveguide do not overlap; and a third optical waveguide which is optically coupled in the combining means to the second optical waveguides and independent of the optical waveguide sensors, said third optical waveguide defining at least one of said third and fourth light paths and having light transmitted therethrough along an optical path length producing coherent interference in said combining means between selected pulses in the second and third optical waveguides, thereby providing a phase difference signal which corresponds to conditions causing variation of light transmission characteristics in specific optical waveguide sensors.
Claim 17
Independent Claim
85 words
An apparatus as defined in either of Claims 5 or 15, wherein said at least one third optical waveguide comprises a third and a fourth optical waveguide, each said third and fourth optical waveguide defining at least a portion of said third and fourth light paths, thereby providing for monitoring of environmental effects on the first fiber-optic sensor by means of light from the third optical waveguide, and monitoring environmental effects on the second fiber-optic sensor by means of light from the fourth optical waveguide.
Claim 18
Independent Claim
183 words
A method for remotely sensing environmental effects on a pair of environmentally sensitive sensors in , a distributed sensor system, comprising the steps of: propagating light from a light source through first and second light paths defined at least in part by a first plurality of optical waveguides, said first and second light paths influenced by an environmental effect at first and second locations; propagating light through third and fourth light paths defined at least in part by at least a second optical waveguide, said third and fourth light paths substantially equal in length, respectively, to the first and second light paths, and not subject to the same environmental effects as the first and second light paths; propagating light from the first plurality of optical waveguide segments to an optical connection with the second waveguide segment through a third optical waveguide segment only; and combining light from said first, second, third and fourth light paths so as to coherently couple light only from light paths substantially equal in length to a specific one of said first and second light paths at any time.
Claim 19
Independent Claim
183 words
A method for remotely sensing environmental effects on a pair of environmentally sensitive sensors in , a distributed sensor system, comprising the steps of: propagating light from a light source through first and second light paths defined at least in part by a first plurality of optical waveguides, said first and second light paths influenced by an environmental effect at first and second locations; propagating light through third and fourth light paths defined at least in part by at least a second optical waveguide, said third and fourth light paths substantially equal in length, respectively, to the first and second light paths, and not subject to the same environmental effects as the first and second light paths; propagating light from the first plurality of optical waveguide segments to an optical connection with the second waveguide segment through a third optical waveguide segment only; and combining light from said first, second, third and fourth light paths so as to coherently couple light only from light paths substantially equal in length to a specific one of said first and second light paths at any time.
Claim 20
Dependent Claim
50 words
A method for remotely sensing environmental effects as defined in Claim 17, wherein the step of propagating light through third and fourth light paths comprises the steps of: propagating light through said third light path at a first time; and propagating light through said second path at a second time.
Claim 21
Independent Claim
170 words
A method of identifying conditions influencing sensors in a distributed sensor system, the method comprising the steps of: transmitting a light signal into first and second optical waveguide segments having at least first and second transmission segments and at least first and second sensor segments, said sensor segments sensitive to environmental effects; transmitting a light signal into a third optical waveguide segment which is mechanically independent from said sensor segments and which defines first and .. second receiver light paths which are substantially equal in length, respectively, to light paths in said first and second waveguide segments, said third waveguide segment not subject to the same environmental effects as the first and second sensor segments; and optically coupling light from the first and second optical waveguide segments and light from the first and second receiver light paths, thereby producing an optical output signal representing conditions causing variation of light transmission characteristics in the sensor segments, said output signal being coherent for said first and second sensor segments at different times.
Claim 22
Independent Claim
170 words
A method of identifying conditions influencing sensors in a distributed sensor system, the method comprising the steps of: transmitting a light signal into first and second optical waveguide segments having at least first and second transmission segments and at least first and second sensor segments, said sensor segments sensitive to environmental effects; transmitting a light signal into a third optical waveguide segment which is mechanically independent from said sensor segments and which defines first and .. second receiver light paths which are substantially equal in length, respectively, to light paths in said first and second waveguide segments, said third waveguide segment not subject to the same environmental effects as the first and second sensor segments; and optically coupling light from the first and second optical waveguide segments and light from the first and second receiver light paths, thereby producing an optical output signal representing conditions causing variation of light transmission characteristics in the sensor segments, said output signal being coherent for said first and second sensor segments at different times.
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