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US5555086A
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Coherence multiplexed interferometric signal processing system and method
Assignee: Northrop Grumman Guidance and Electronics Co Inc
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Filing: 1992-12-24
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Granted: 1996-09-10
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Expires: 2012-12-24
Abstract
Abstract A fiber optic sensor system includes a plurality of interferometric sensors arranged in an array to monitor a selected parameter and means for providing two-mode optical signals to each of the interferometric sensors. The two modes have different propagation velocities so that each sensor produces an optical signal indicative of changes in the parameter. A return optical fiber receives signals output from each of the plurality of interferometric sensors. The optical signals in the return fiber are separated and input to a Fourier transform lens that forms a plurality of spatially separated fringe patterns on a grating. Each fringe pattern corresponds to the optical signal output from a selected sensor. A photodetector array monitors the fringe patterns simultaneously and continuously to detect changes in the parameter. A phase modulator modulates the phase of one of the optical sensor signals output from the sensor array. Changes in the parameter either shift the locations of the fringe patterns or produce and additional phase modulation in the fringe patterns.
Inventors
- 👤 Karlheinz vonBieren
- 👤 Donald A. Frederick
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 10:20
CPC Classifications
G; G01; G01D; G01D5/00; G01D5/26; G01D5/32; G01D5/34; G01D5/353; G01D5/35383
Claims Analysis
Total Claims: 36
Claim 1
Independent Claim
172 words
A fiber optic sensing system for monitoring a selected parameter, comprising: a plurality of fiber optic interferometric sensors connected in an array; means for introducing two-mode optical signals into each of the plurality of fiber optic interferometric sensors such that each of the plurality of fiber optic interferometric sensors produces an optical signal indicative of changes in the parameter; a Fourier transform lens arranged to receive the optical signals indicative of changes in the parameter and to provide a lens output signal that includes a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected one of the plurality of interferometric sensors; a transmission grating arranged to receive the plurality of spatially separated interference fringe patterns, the transmission grating having a groove spacing corresponding to the spatially separated interference fringe patterns such that the fringe patterns are transmitted through the grating; and means for monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 2
Dependent Claim
172 words
A fiber optic sensing system for monitoring a selected parameter, comprising: a plurality of fiber optic interferometric sensors connected in an array; means for introducing two-mode optical signals into each of the plurality of fiber optic interferometric sensors such that each of the plurality of fiber optic interferometric sensors produces an optical signal indicative of changes in the parameter; a Fourier transform lens arranged to receive the optical signals indicative of changes in the parameter and to provide a lens output signal that includes a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected one of the plurality of interferometric sensors; a transmission grating arranged to receive the plurality of spatially separated interference fringe patterns, the transmission grating having a groove spacing corresponding to the spatially separated interference fringe patterns such that the fringe patterns are transmitted through the grating; and means for monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 3
Dependent Claim
182 words
A sensing system for monitoring a selected parameter, comprising: a plurality of interferometric sensors connected in an array; means for providing two-mode optical signals to each of the plurality of interferometric sensors, each of the plurality of interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical sensor signal indicative of changes in the parameter; a single return optical fiber for receiving output signals from each of the plurality of interferometric sensors; means for combining the optical sensor signals output from the plurality of interferometric sensors to produce a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor, including: a Fourier transform lens arranged to receive the optical sensor signals; and a grating arranged in relation to the Fourier transform lens such that the fringe patterns form spatially separated on the grating; and means for monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 4
Dependent Claim
182 words
A sensing system for monitoring a selected parameter, comprising: a plurality of interferometric sensors connected in an array; means for providing two-mode optical signals to each of the plurality of interferometric sensors, each of the plurality of interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical sensor signal indicative of changes in the parameter; a single return optical fiber for receiving output signals from each of the plurality of interferometric sensors; means for combining the optical sensor signals output from the plurality of interferometric sensors to produce a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor, including: a Fourier transform lens arranged to receive the optical sensor signals; and a grating arranged in relation to the Fourier transform lens such that the fringe patterns form spatially separated on the grating; and means for monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 5
Dependent Claim
65 words
The sensing system of claim 2 further including a modal filter for separating optical signals in the return fiber into a first optical sensor signal output and a second optical sensor signal output such that the first optical sensor signal output is in a first one of the two modes and the second optical sensor signal output is in the other of the two modes.
Claim 6
Dependent Claim
43 words
The sensing system of claim 3 including a first optical fiber for guiding the first optical sensor signal output and a second optical fiber for guiding the second optical sensor signal output along parallel optical paths for input to the Fourier transform lens.
Claim 7
Dependent Claim
64 words
The sensing system of claim 4 wherein the means for monitoring the plurality of spatially separated interference fringe patterns includes: phase modulator means for modulating the phase of one of the optical sensor signals; a plurality of photodetectors arranged such that each one of the plurality of photodetectors detects a corresponding fringe pattern; and means for demodulating signals output from the plurality of photodetectors.
Claim 8
Dependent Claim
71 words
The sensing system of claim 2 wherein the means for monitoring the plurality of spatially separated interference fringe patterns includes: phase modulator means for modulating the phase of the optical sensor signals before they are incident upon the Fourier transform lens; a plurality of photodetectors arranged such that each one of the plurality of photodetectors detects a corresponding fringe pattern; and means for demodulating signals output from the plurality of photodetectors.
Claim 9
Dependent Claim
24 words
The sensing system of claim 2 wherein the plurality of interferometric sensors comprises a plurality of fiber optic interferometers arranged in a parallel array.
Claim 10
Dependent Claim
33 words
The sensing system of claim 7 wherein each of the fiber optic sensors guides a first polarization mode along a first optical path and a second polarization mode along a second optical path.
Claim 11
Dependent Claim
39 words
The sensing system of claim 2 wherein the plurality of interferometric sensors comprises a plurality of fiber optic interferometers arranged in a series array, each fiber optic interferometer being formed to produce an output signal of a selected wavelength.
Claim 12
Dependent Claim
33 words
The sensing system of claim 9 wherein each of the fiber optic interferometers guides a first polarization mode along a first optical path and a second polarization mode along a second optical path.
Claim 13
Dependent Claim
32 words
The sensing system of claim 10 including means for separating optical signals in the return optical fiber into a plurality of signal portions having both the first and second polarization modes therein.
Claim 14
Dependent Claim
259 words
A sensing system for monitoring a selected parameter, comprising: a plurality of interferometric sensors arranged in an array, the plurality of fiber optic interferometers being arranged in a series array, each fiber optic interferometer being formed to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path, each fiber optic interferometer being formed to produce an output optical signal of a selected wavelength; means for providing two-mode optical signals to each of the plurality of interferometric sensors, each of the plurality of interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical signal indicative of changes in the parameter; a single return optical fiber for receiving output signals from each of the plurality of interferometric sensors; means for separating optical signals in the return optical fiber into a plurality of signal portions having both the first and second polarization modes therein; means for combining the plurality of signal portions to produce a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor, including: a Fourier transform lens arranged to receive the first and second optical sensor signal outputs; and a grating arranged in relation to the Fourier transform lens such that the fringe patterns form spatially separated on the grating; and means for monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 15
Dependent Claim
259 words
A sensing system for monitoring a selected parameter, comprising: a plurality of interferometric sensors arranged in an array, the plurality of fiber optic interferometers being arranged in a series array, each fiber optic interferometer being formed to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path, each fiber optic interferometer being formed to produce an output optical signal of a selected wavelength; means for providing two-mode optical signals to each of the plurality of interferometric sensors, each of the plurality of interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical signal indicative of changes in the parameter; a single return optical fiber for receiving output signals from each of the plurality of interferometric sensors; means for separating optical signals in the return optical fiber into a plurality of signal portions having both the first and second polarization modes therein; means for combining the plurality of signal portions to produce a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor, including: a Fourier transform lens arranged to receive the first and second optical sensor signal outputs; and a grating arranged in relation to the Fourier transform lens such that the fringe patterns form spatially separated on the grating; and means for monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 16
Independent Claim
281 words
A method for forming an interferometric sensing system for monitoring a selected parameter, comprising the steps of: arranging a plurality of fiber optic interferometric sensors in an array to monitor the selected parameter; providing two-mode optical signals to each of the plurality of fiber optic interferometric sensors, each of the plurality of fiber optic interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical signal indicative of changes in the parameter; receiving output signals output from each of the plurality of interferometric sensors on a return optical fiber; coupling optical signals having a first polarization in the return fiber into a first fiber to form a first optical sensor signal output; coupling optical signals having a second polarization in the return fiber into a second fiber to form a second optical sensor signal output; arranging the first and second fibers such the first and second optical sensor signal outputs are emitted from the first and second fibers so that the first and second optical sensor signal outputs interfere to form a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor; arranging a Fourier transform lens to receive the interference fringe patterns and produce a Fourier transform thereof; arranging a transmission grating to receive the Fourier transform of the interference fringe patterns thereon; providing a groove spacing in the transmission grating equal to the spatial separation of the interference fringe patterns on the grating; and monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 17
Independent Claim
281 words
A method for forming an interferometric sensing system for monitoring a selected parameter, comprising the steps of: arranging a plurality of fiber optic interferometric sensors in an array to monitor the selected parameter; providing two-mode optical signals to each of the plurality of fiber optic interferometric sensors, each of the plurality of fiber optic interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical signal indicative of changes in the parameter; receiving output signals output from each of the plurality of interferometric sensors on a return optical fiber; coupling optical signals having a first polarization in the return fiber into a first fiber to form a first optical sensor signal output; coupling optical signals having a second polarization in the return fiber into a second fiber to form a second optical sensor signal output; arranging the first and second fibers such the first and second optical sensor signal outputs are emitted from the first and second fibers so that the first and second optical sensor signal outputs interfere to form a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor; arranging a Fourier transform lens to receive the interference fringe patterns and produce a Fourier transform thereof; arranging a transmission grating to receive the Fourier transform of the interference fringe patterns thereon; providing a groove spacing in the transmission grating equal to the spatial separation of the interference fringe patterns on the grating; and monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 18
Independent Claim
217 words
A method for forming a sensing system, comprising the steps of: arranging a plurality of interferometric sensors in an array to monitor a selected parameter; providing two-mode optical Signals to each of the plurality of interferometric sensors, each of the plurality of interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical signal indicative of changes in the parameter; receiving output signals output from each of the plurality of interferometric sensors on a single return optical fiber; separating optical signals in the return fiber into a first optical sensor signal output and a second optical sensor signal output; combining the first optical sensor signal output and the second optical sensor signal output to produce a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor by the steps of; receiving the first and second optical sensor signal outputs with a Fourier transform lens; and arranging a grating in relation to the Fourier transform lens such that the fringe patterns form on the grating with the fringe patterns being spatially separated; and monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 19
Independent Claim
217 words
A method for forming a sensing system, comprising the steps of: arranging a plurality of interferometric sensors in an array to monitor a selected parameter; providing two-mode optical Signals to each of the plurality of interferometric sensors, each of the plurality of interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical signal indicative of changes in the parameter; receiving output signals output from each of the plurality of interferometric sensors on a single return optical fiber; separating optical signals in the return fiber into a first optical sensor signal output and a second optical sensor signal output; combining the first optical sensor signal output and the second optical sensor signal output to produce a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor by the steps of; receiving the first and second optical sensor signal outputs with a Fourier transform lens; and arranging a grating in relation to the Fourier transform lens such that the fringe patterns form on the grating with the fringe patterns being spatially separated; and monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 20
Dependent Claim
76 words
The method of claim 14 wherein the step of separating optical signals in the return fiber into a first optical sensor signal output and a second optical sensor signal output includes using a modal filter to divide the optical signals in the return fiber such that the first optical sensor signal output is in a first one of the two modes and the second optical sensor signal output is in the other of the two modes.
Claim 21
Dependent Claim
42 words
The method of claim 15 including guiding the first optical sensor signal output with a first optical fiber and guiding the second optical sensor signal output with a second optical fiber along parallel optical paths for input to the Fourier transform lens.
Claim 22
Dependent Claim
65 words
The method of claim 16 wherein the step of monitoring the plurality of spatially separated interference fringe patterns includes the steps of: modulating the phase of one of the optical sensor signals; detecting the fringe patterns with a plurality of photodetectors arranged such that each one of the plurality of photodetectors detects a corresponding fringe pattern; and demodulating signals output from the plurality of photodetectors.
Claim 23
Dependent Claim
65 words
The method of claim 14 wherein the step of monitoring the plurality of spatially separated interference fringe patterns includes the steps of: modulating the phase of one of the optical sensor signals; detecting the fringe patterns with a plurality of photodetectors arranged such that each one of the plurality of photodetectors detects a corresponding fringe pattern; and demodulating signals output from the plurality of photodetectors.
Claim 24
Dependent Claim
26 words
The method of claim 14 including the step of forming the interferometric sensors to comprise a plurality of fiber optic interferometers arranged in a parallel array.
Claim 25
Dependent Claim
37 words
The method of claim 19 including the step of forming each of the fiber optic sensors to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path.
Claim 26
Dependent Claim
37 words
The method of claim 14 including the step of forming each of the fiber optic sensors to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path.
Claim 27
Dependent Claim
37 words
The method of claim 21 including the step of forming each of the fiber optic sensors to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path.
Claim 28
Dependent Claim
32 words
The method of claim 20 including the step of separating optical signals in the return optical fiber into a plurality of signal portions having both the first and second polarization modes therein.
Claim 29
Independent Claim
285 words
A method for forming a sensing system, comprising the steps of: arranging a plurality of interferometric sensors in an array to monitor a selected parameter; providing two-mode optical signals to each of the plurality of interferometric sensors, each of the plurality of interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical signal indicative of changes in the parameter; forming the interferometric sensors to comprise a plurality of fiber optic interferometers arranged in a parallel array; forming each of the fiber optic sensors to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path; receiving output signals output from each of the plurality of interferometric sensors on a single return optical fiber; separating optical signals in the return optical fiber into a plurality of signal portions having both the first and second polarization modes therein; separating optical signals in the return fiber into a first optical sensor signal output and a second optical sensor signal output; combining the first optical sensor signal output and the second optical sensor signal output to produce a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor by the steps of: receiving the first and second optical sensor signal outputs with a Fourier transform lens; and arranging a grating in relation to the Fourier transform lens such that the fringe patterns form on the grating with the fringe patterns being spatially separated; and monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 30
Independent Claim
285 words
A method for forming a sensing system, comprising the steps of: arranging a plurality of interferometric sensors in an array to monitor a selected parameter; providing two-mode optical signals to each of the plurality of interferometric sensors, each of the plurality of interferometric sensors being formed such that the two modes have different propagation velocities therein and such that each of the plurality of interferometric sensors produces an optical signal indicative of changes in the parameter; forming the interferometric sensors to comprise a plurality of fiber optic interferometers arranged in a parallel array; forming each of the fiber optic sensors to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path; receiving output signals output from each of the plurality of interferometric sensors on a single return optical fiber; separating optical signals in the return optical fiber into a plurality of signal portions having both the first and second polarization modes therein; separating optical signals in the return fiber into a first optical sensor signal output and a second optical sensor signal output; combining the first optical sensor signal output and the second optical sensor signal output to produce a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected sensor by the steps of: receiving the first and second optical sensor signal outputs with a Fourier transform lens; and arranging a grating in relation to the Fourier transform lens such that the fringe patterns form on the grating with the fringe patterns being spatially separated; and monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 31
Dependent Claim
215 words
A sensing system for monitoring a selected parameter, comprising: a plurality of fiber optic interferometric sensors arranged in an array, the plurality of fiber optic interferometers being arranged in a series array, each fiber optic interferometer being formed to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path; means for introducing two-mode optical signals into each of the plurality of fiber optic interferometric sensors such that each of the plurality of fiber optic interferometric sensors produces an optical signal indicative of changes in the parameter; a return optical fiber for receiving output signals from each of the plurality of interferometric sensors; a mode filter connected to the return fiber for separating output signals in the return optical fiber a first signal of a first polarization and a second signal of a second polarization; a Fourier transform lens arranged to receive the first and second signals output from the mode filter and combine them to produce a plurality of spatially separated fringe patterns; a grating arranged in relation to the Fourier transform lens such that the fringe patterns form spatially separated on the grating; and means for monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 32
Dependent Claim
215 words
A sensing system for monitoring a selected parameter, comprising: a plurality of fiber optic interferometric sensors arranged in an array, the plurality of fiber optic interferometers being arranged in a series array, each fiber optic interferometer being formed to guide a first polarization mode along a first optical path and a second polarization mode along a second optical path; means for introducing two-mode optical signals into each of the plurality of fiber optic interferometric sensors such that each of the plurality of fiber optic interferometric sensors produces an optical signal indicative of changes in the parameter; a return optical fiber for receiving output signals from each of the plurality of interferometric sensors; a mode filter connected to the return fiber for separating output signals in the return optical fiber a first signal of a first polarization and a second signal of a second polarization; a Fourier transform lens arranged to receive the first and second signals output from the mode filter and combine them to produce a plurality of spatially separated fringe patterns; a grating arranged in relation to the Fourier transform lens such that the fringe patterns form spatially separated on the grating; and means for monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 33
Dependent Claim
184 words
The fiber optic sensing system of claim 1 wherein the fiber optic sensor array includes a fiber optic sensor that comprises: a first single mode optical fiber that guides an optical signal in the LP 01 mode; a length of two-mode optical fiber having first and second ends, the first end being connected to an end of the single mode optical fiber, the ends of the single mode fiber and the two-mode optical fiber being arranged such that a first portion of the optical signal guided by the single mode optical fiber couples into the LP 01 mode in the two-mode optical fiber and a second portion of the optical signal guided by the single mode optical fiber couples into the LP 11 mode in the two-mode optical fiber; and a second single mode fiber having an end connected to the second end of the two-mode optical fiber such that portions of the both the optical signals in the LP 01 mode and the LP 11 mode in the two-mode optical fiber couple into the LP 01 mode in the second single mode fiber.
Claim 34
Independent Claim
168 words
A method for forming a sensing system, comprising the steps of: connecting a plurality of fiber optic interferometric sensors in an array; introducing two-mode optical signals into each of the plurality of fiber optic interferometric sensors such that each of the plurality of fiber optic interferometric sensors produces an optical signal indicative of changes in the parameter; arranging a Fourier transform lens to receive the optical signals indicative of changes in the parameter and to provide a lens output signal that includes a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected one of the plurality of interferometric sensors; arranging a transmission grating to receive the plurality of spatially separated interference fringe patterns, the transmission grating having a groove spacing corresponding to the spatially separated interference fringe patterns such that the fringe patterns are transmitted through the grating; and monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 35
Independent Claim
168 words
A method for forming a sensing system, comprising the steps of: connecting a plurality of fiber optic interferometric sensors in an array; introducing two-mode optical signals into each of the plurality of fiber optic interferometric sensors such that each of the plurality of fiber optic interferometric sensors produces an optical signal indicative of changes in the parameter; arranging a Fourier transform lens to receive the optical signals indicative of changes in the parameter and to provide a lens output signal that includes a plurality of spatially separated interference fringe patterns, each interference fringe pattern corresponding to the optical signal output from a selected one of the plurality of interferometric sensors; arranging a transmission grating to receive the plurality of spatially separated interference fringe patterns, the transmission grating having a groove spacing corresponding to the spatially separated interference fringe patterns such that the fringe patterns are transmitted through the grating; and monitoring the plurality of spatially separated interference fringe patterns simultaneously and continuously to detect changes in the parameter.
Claim 36
Dependent Claim
182 words
The method of claim 27 wherein the step of connecting a plurality of fiber optic interferometric sensors in an array includes the steps of: providing a first single mode-optical fiber that guides an optical signal in the LP 01 mode; connecting a first end of a length of two-mode optical fiber to an end of the single mode optical fiber, the ends of the single mode fiber and the two-mode optical fiber being arranged such that a first portion of the optical signal guided by the single mode optical fiber couples into the LP 01 mode in the two-mode optical fiber and a second portion of the optical signal guided by the single mode optical fiber couples into the LP 11 mode in the two-mode optical fiber; and connecting an end of a second single mode fiber to a second end of the two-mode optical fiber such that portions of the both the optical signals in the LP 01 mode and the LP 11 mode in the two-mode optical fiber couple into the LP 01 mode in the second single mode fiber.
References Cited (Backward Citations)
US4862424A
Cited
US4747688A
Cited
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