EP0251632A2
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EP
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Distributed sensor array and method using a pulsed signal source
Assignee: Leland Stanford Junior University
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Filing: 1987-06-22
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Granted: —
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Expires: 2007-06-22
Abstract
Abstract A distributed sensor system using pulsed optical signals optionally produced by a short coherence length source (100) to provide a phase difference output signal representative of conditions affecting a selected sensor. In one preferred embodiment, an array of fiber-optical sensors (110) are organized in a ladder configuration, with the sensors (110) positioned in spaced relation and defining the rungs of the ladder. Light pulses (201) transmitted through the sensors (110) are multiplexed onto a return arm (114) of the ladder. The multiplexed signals (114) are received by an optical fiber compensating interferometer (200) which coherently couples portions of adjacent multiplexed light signals to produce a phase difference signal representing conditions influencing selected sensors (110). In other preferred embodiments, the system is configured to define a plurality of adjacent Mach-Zehnder interferometers (110) which provide output signal pairs (205) which coherently couple 'to yield a phase difference signal directly representing the environmental effects on a particular sensor (117). Functional equivalents of the Mach-Zehnder interferometer configurations comprise configurations including adjacent Michelson interferometers. A phase and amplitude modulation technique and apparatus (Figure 8) is disclosure for providing heterodyned output signals from the distributed sensor system. I
Inventors
- 👤 Byoung Yoon Kim
- 👤 Herbert John Shaw
- 👤 Moshe Tur
- 👤 Janet L. Brooks
- 👤 Kenneth A. Fesler
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-31 20:43
CPC Classifications
G; G01; G01D; G01D5/00; G01D5/26; G01D5/32; G01D5/34; G01D5/353; G01D5/35383
Claims Analysis
Total Claims: 21
Claim 1
Independent Claim
183 words
An apparatus for remotely sensing environmental effects comprising: a source of pulsed optical signals (100); a first optical waveguide (102) optically coupled to the signal source; an environmentally sensitive waveguide segment (110b) optically coupled to the first optical waveguide, said sensitive segment influencing optical signals propagating within said sensitive segment in response to a particular environmental condition; a second optical waveguide (110a) optically coupled to the first optical waveguide in a configuration such that the second optical waveguide (110a) and the environmentally sensitive waveguide segment (11 Ob) from at least portions of arms of a first unbalanced interferometer; and a second unbalanced interferometer (200) optically coupled to the first unbalanced interferometer for receiving optical signals from said first interferometer, wherein the second interferometer (200) provides a pair of optical paths (206, 208) having an optical path length difference which substantially matches an optical path length difference defined by the first interferometer, such that the second interferometer (200) combines optical signals received from the first interferometer to form a phase difference output signal representative of environmental influence on the environmentally sensitive waveguide segment (110b).
Claim 2
Independent Claim
183 words
An apparatus for remotely sensing environmental effects comprising: a source of pulsed optical signals (100); a first optical waveguide (102) optically coupled to the signal source; an environmentally sensitive waveguide segment (110b) optically coupled to the first optical waveguide, said sensitive segment influencing optical signals propagating within said sensitive segment in response to a particular environmental condition; a second optical waveguide (110a) optically coupled to the first optical waveguide in a configuration such that the second optical waveguide (110a) and the environmentally sensitive waveguide segment (11 Ob) from at least portions of arms of a first unbalanced interferometer; and a second unbalanced interferometer (200) optically coupled to the first unbalanced interferometer for receiving optical signals from said first interferometer, wherein the second interferometer (200) provides a pair of optical paths (206, 208) having an optical path length difference which substantially matches an optical path length difference defined by the first interferometer, such that the second interferometer (200) combines optical signals received from the first interferometer to form a phase difference output signal representative of environmental influence on the environmentally sensitive waveguide segment (110b).
Claim 3
Dependent Claim
28 words
An apparatus for remotely sensing environmental effects as defined in claim 1, wherein the environmentally sensitive waveguide segment comprises a portion (105) of the first optical waveguide (102).
Claim 4
Dependent Claim
53 words
An apparatus for remotely sensing environmental effects as defined in claim 2, wherein the first interferometer comprises a third optical waveguide (110b) optically coupled to the first waveguide (102) at a location such that the environmentally sensitive waveguide (105) is located between the coupling locations of the second and third waveguides (110a, 110b).
Claim 5
Dependent Claim
80 words
An apparatus for remotely sensing environmental effects as defined in claim 3, further comprising a fourth optical waveguide (114) optically coupled to extend between ends of the second and third waveguides (110a, 110b) which are opposite from the ends coupled to the first waveguide (102), and wherein the first interferometer defines a first optical path through the second waveguide (110a), and a second optical path through the environmentally sensitive waveguide segment (105), and the third and fourth waveguides (110b, 114).
Claim 6
Independent Claim
62 words
An apparatus for remotely sensing environmental effects as defined in any of claims 1-4, wherein the optical signals combined in the second interferometer (200) include only one optical signal which propagated through the environmentally sensitive waveguide segment, thereby making the phase difference output signal directly representative of environmental conditions influencing said optical signal as it propagated through said environmentally sensitive waveguide segment.
Claim 7
Independent Claim
29 words
An apparatus for remotely sensing environmental effects as defined in any of claims 1-5, wherein the source of pulsed optical signals (100) comprises a short coherence length light source.
Claim 8
Independent Claim
62 words
An apparatus for remotely sensing environmental effects as defined in any of claims 1-6, further comprising means (101) for controlling the source of pulsed optical signals (100) so that optical signals produced by a first optical pulse from said signal source do not interfere in the first interferometer with optical signals produced by a second optical pulse from said signal source (100).
Claim 9
Independent Claim
98 words
An apparatus for remotely sensing environmental effects as defined in any of claims 1-7, further comprising means (101) for synchronizing production of said pulsed optical signals so that a last signal reaching the second interferometer (200) from a first pulsed optical signal is spaced from a first signal reaching the second interferometer (200) from a second pulsed optical signal by an amount permitting said last and first signals to be combined in said second interferometer (200) to obtain a phase difference output signal between those signals and to provide for a substantially continuous duty cycle in apparatus operation.
Claim 10
Independent Claim
45 words
An apparatus for remotely sensing environmental effects as defined in any of claims 1-8, wherein the first interferometer receives a single optical pulse signal (201) from the signal source (100) and provides a corresponding pair of optical pulse signals (203) to the second interferometer (200).
Claim 11
Independent Claim
87 words
An apparatus for remotely sensing environmental conditions as defined in any of claims 1-9, further comprising: a detector (212) optically coupled to the second interferometer (200) for forming an output which corresponds to the phase difference of the combined optical signals; and a circuit (Figure 8) for amplitude modulating the output to produce a first signal having selected harmonics which contain both sine and cosine components of the outputs, thereby providing for analysis of the output signal to identify environmental effects influencing the environmentally sensitive waveguide segment.
Claim 12
Dependent Claim
72 words
An apparatus for remotely sensing environmental conditions as defined in claim 10, further comprising: a signal generator (308) for providing a phase modulation signal at a selected modulation frequency; a phase modulator (310), responsive to the signal generator (308) for phase modulating the optical signal in one of said waveguides at the selected modulation frequency; and wherein the circuit (Figure 8) functions to amplitude modulate the output at the selected modulation frequency.
Claim 13
Independent Claim
210 words
An apparatus for remotely sensing environmental effects as defined in any of claims 4-11, further comprising: a plurality of sensing regions (105) located in spaced relation in the first optical waveguide (102), each of said sensing regions (105) being sensitive to an environmental effect so as to influence optical signals propagating in said sensing region (105) in response to said environmental effect; a plurality of optical waveguide segments (110), with each said optical waveguide segment coupled at one end to the first optical waveguide (102) at locations separated by at least one sensing region (105) from other optical waveguide segments (110), and with each said optical waveguide segment (110) coupled at its other end to the fourth optical waveguide (114), whereby each adjacent pair of optical waveguide segments (110) respectively comprise at least a portion of a pair of arms of an unbalanced optical interferometer defining an optical path length difference which substantially matches the path length difference of the first and second optical paths so that optical signals from each of the unbalanced optical interferometers are combined, at different times for each interferometer, in the second optical interferometer (200) to form phase difference signals representative of environmental influence on the environmentally sensitive segment (105) of the corresponding unbalanced interferometer.
Claim 14
Independent Claim
198 words
An apparatus for remotely sensing environmental conditions as defined in any of claims 1-13, further comprising: a plurality of fiber-optic sensing interferometers (110), each said sensing interferometer defining a pair of optical paths (109, 115), and at least a portion of each said interferometer having light transmission characteristics which vary in response to environmental conditions, with each said sensing interferometer having input and output terminals which are optically coupled together to form a ladder network, said input terminals being optically coupled to the source of pulsed optical signals (100); and wherein the second unbalanced interferometer (200) comprises at least one fiber-optic compensating interferometer (200) optically coupled to the output terminals of the sensing interferometers and defining a pair of optical paths (206, 208) whose optical path length difference substantially matches an optical path length difference of the pair of optical paths (109, 115) in a selected sensing interferometer, such that portions of a pulsed optical signal (201) transmitted from the optical signal source (100) through the sensor system will coherently couple at an output (204) of the compensating interferometer (200) providing an optical signal representative of conditions causing change in light transmission characteristics of said selected sensing interferometer.
Claim 15
Dependent Claim
42 words
A distributed sensor system as defined in claim 13, wherein the path length difference between the pair of optical paths in each sensing interferometer substantially equals the optical path length difference between the pair of optical paths in the compensating interferometer (200).
Claim 16
Dependent Claim
256 words
An apparatus for remotely sensing environmental effects as defined in claim 3, further comprising: means (222) optically coupled to the other ends of each of said second and third optical waveguides (220a, 220b) for reflecting optical signals from said second and third waveguide back into said second and third waveguide, such that the first and second waveguides (102, 220a) and associated reflecting means (222) form a first optical signal path carrying a portion of a pulsed optical signal from the first optical waveguide (102) into the second optical waveguide (220a) until reflected back into the first waveguide (102), and such that the first and third waveguides 102, 220b) and associated reflecting means (222) form a second optical signal path carrying a portion of said pulsed optical signal through the environmentally sensitive waveguide segment (224) and into the third waveguide (220b) until reflected back through said sensitive waveguide segment (224) into the first waveguide (102); and wherein the second interferometer (200) includes waveguides (206, 2088) defining third and fourth optical signal paths for carrying portions of each of said reflected, pulsed optical signals (203), and wherein the optical path length difference between the third and fourth signal paths is substantially equal to the optical path length difference between the first and second optical signal paths so that pulsed optical signals from the first interferometer are coherently coupled in the second interferometer (200) to provide an optical output signal representative of the environmental effects which influenced the optical signal that propagated through the environmentally sensitive waveguide segment (224).
Claim 17
Dependent Claim
35 words
An apparatus for remotely sensing environmenjal effects as defined in claim 15 wherein the first interferometer is configured to define a Michelson interferometer and the second interferometer (200) is configured to define a Mach-Zehnder interferometer.
Claim 18
Dependent Claim
29 words
An apparatus for remotely sensing environmental effects as defined in claim 15 or 16 wherein the source of pulsed optical signals (100) comprises a short coherence length light source.
Claim 19
Dependent Claim
212 words
An apparatus for remotely sensing environmental effects as defined in claim 1, wherein the first unbalanced interferometer comprises at least one Michelson interferometer defining a first optical path passing through the second optical waveguide (225) and a second optical path passing through the environmentally sensitive waveguide segment (227), which optical paths are optically coupled to the first optical waveguide (102) to receive at least a portion of a pulsed optical signal (201) and to return a pair of pulsed optical signals (205) to the first optical waveguide (102); and wherein the second unbalanced interferometer (200) is optically coupled to receive said pair of pulsed optical signals (205) from the first waveguide (102), wherein said second interferometer (200) includes waveguides (206, 208) defining third and fourth optical signal paths for carrying portions of said pair of optical signals (205), and wherein the optical path length difference between the third and fourth signal paths is substantially equal to the optical path length difference between the first and second optical signal paths so that pulsed optical signals (205) from the first interferometer are coherently coupled in the second interferometer (200) to provide an optical output signal representative of the environmental effects which influenced the optical signal that propagated through the environmentally sensitive waveguide segment (227).
Claim 20
Dependent Claim
17 words
A distributed sensor system as defined in claim 18 wherein said second interferometer comprises a Mach-Zehnder interferometer.
Claim 21
Dependent Claim
29 words
An apparatus for remotely sensing environmental effects as defined in claim 19 or 20 wherein the source of pulsed optical signals (100) comprises a short coherence length light source.
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