Multi-channel fiber optic sensor system
First Claim
1. A data gathering system, including:
- a main optical fiber through which an interrogating light signal may propagate in a first direction;
at least three reflectors formed on the main fiber such that each reflector is separated from the nearest reflector thereto by a section of the main fiber having length L, where each reflector is capable of operating in an active state in which the reflector will reflect a portion of the interrogating light signal so that the reflected portion will propagate in a direction opposite the first direction, and each reflector is also capable of operating in a deactivated state in which the interrogating light signal may propagate substantially unhindered past the reflector and where each reflector includes a substrate bonded to the main fiber through which acoustic signals may propagate, and means for generating both a first acoustic wave which will propagate from the substrate into an interaction portion of the main fiber so as to propagate in the main fiber in a second direction at an angle approximately 45°
with respect to the axis, and a second acoustic wave which will propagate from the substrate into the interaction portion so as to propagate in the main fiber in a third direction at an angle approximately 45°
with respect to the axis and approximately perpendicular to the second direction; and
a phase sensitive detector capable of measuring phase modulations associated with pairs of reflected signals, where each reflected signal in each pair originates at a pair of adjacent reflectors, and where the energy in both reflected signals in each pair is reflected from the same interrogating light signal.
1 Assignment
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Accused Products
Abstract
A time division multiplexing, fiber optic data gathering system, including two or more sensors formed on an optical fiber, and a phase sensitive detector. Each sensor includes two reflectors separated by a section of the fiber having length L. Each reflector may be activated so that when an interrogating light signal propagates in a first direction past the activated reflector, a portion of the interrogating light signal will be reflected back into a direction opposite the first direction. Each reflector may also be deactivated so that the interrogating signal may propagate unhindered past the deactivated reflector. Variations in the optical path length between the reflectors of a sensor, due to changes in an external parameter of interest, will cause phase modulations that are extracted in the phase sensitive detector by homodyne or heterodyne techniques. In a preferred embodiment, the activated reflectors produce a specific type of acoustic field resulting from superposition of two acoustic waves, which acoustic field will interact with the interrogating light signal so as to reflect a portion of the interrogating light signal by 180°.
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Citations
14 Claims
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1. A data gathering system, including:
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a main optical fiber through which an interrogating light signal may propagate in a first direction; at least three reflectors formed on the main fiber such that each reflector is separated from the nearest reflector thereto by a section of the main fiber having length L, where each reflector is capable of operating in an active state in which the reflector will reflect a portion of the interrogating light signal so that the reflected portion will propagate in a direction opposite the first direction, and each reflector is also capable of operating in a deactivated state in which the interrogating light signal may propagate substantially unhindered past the reflector and where each reflector includes a substrate bonded to the main fiber through which acoustic signals may propagate, and means for generating both a first acoustic wave which will propagate from the substrate into an interaction portion of the main fiber so as to propagate in the main fiber in a second direction at an angle approximately 45°
with respect to the axis, and a second acoustic wave which will propagate from the substrate into the interaction portion so as to propagate in the main fiber in a third direction at an angle approximately 45°
with respect to the axis and approximately perpendicular to the second direction; anda phase sensitive detector capable of measuring phase modulations associated with pairs of reflected signals, where each reflected signal in each pair originates at a pair of adjacent reflectors, and where the energy in both reflected signals in each pair is reflected from the same interrogating light signal. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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2. A data gathering system, including:
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a main optical fiber having a longitudinal axis and a first end and a second end; a light source for transmitting into the first end of the main fiber an interrogating light signal which propagates in a first direction along the longitudinal axis of the main fiber; at least two sensors formed on the main fiber, each of the sensors including two reflectors separated from each other by a distance L along the longitudinal axis of the main fiber, where each reflector is capable of being switched between an active state in which the reflector will reflect a portion of the interrogating light signal into a direction opposite the first direction, and an inactive state in which the interrogating light signal may propagate substantially unhindered past the reflector, and each reflector includes a substrate bonded to the main fiber through which acoustic signals may propagate, and means for generating both a first acoustic wave which will propagate from the substrate into an interaction portion of the main fiber so as to propagate in the main fiber in a second direction at an angle approximately 45°
with respect to the axis, and a second acoustic wave which will propagate from the substrate into the interaction portion so as to propagate in the main fiber in a third direction at an angle approximately 45°
with respect of the axis and approximately perpendicular to the second direction; and
a phase sensitive detector capable of measuring phase modulations associated with each pair of reflected signals originating at each sensor.
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13. A data generating system, including:
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a main optical fiber having a longitudinal axis and a first end and a second end; a light source capable of transmitting into the first end of the main fiber an interrogating light signal which propagates in a first direction along the longitudinal axis of the main fiber; a number of sensors positioned at separated locations along the main fiber, each sensor including a pair of selectively activatable reflectors, each reflector being capable of reflecting a portion of the interrogating light signal in a direction opposite the first direction, but only when said reflector is in an activated state; and means for measuring the phase associated with each pair of reflected signals originating at one of the sensors, said phase measuring means including; a first directional coupler coupled with the main fiber; a second optical fiber, having a first end and a second end, and coupled to the first directional coupler in such a manner that the reflected light signals will propagate from the main fiber through the first directional coupler and into the first end of the second fiber; a Bragg cell coupled to the second end of the second fiber; a reference optical fiber of length 2L+M coupled to the Bragg cell in such a manner that frequency shifted light diverted in the Bragg cell propagates into the reference optical fiber; a short optical fiber of length M coupled to the Bragg cell in such a manner that light not diverted in the Bragg cell propagates into the short optical fiber; a second directional coupler having two input ports, one coupled to the reference fiber and the other coupled to the short fiber; and a photodetector coupled to an output port of the second directional coupler.
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14. A data gathering system, including:
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a main optical fiber having a longitudinal axis and a first end and a second end; a light source capable of transmitting into the first end of the main fiber an interrogating light signal which propagates in a first direction along the longitudinal axis of the main fiber; a number of sensors positioned at separated locations along the main fiber, each sensor including a pair of selectively activatable reflectors, each reflector being capable of reflecting a portion of the interrogating light signal in a direction opposite the first direction, but only when said reflector is in an activated state; and means for measuring the phase associated with each pair of reflected signals originating at one of the sensors, said phase measuring means including; a first directional coupler coupled with the main fiber; a second optical fiber, having a first end and a second end, and coupled to the first directional coupler in such a manner that the reflected light signals will propagate from the main fiber through the first directional coupler and into the first end of the second fiber; a second directional coupler having an input port coupled with the second end of the second fiber and having two output ports; a reference optical fiber of length 2L+M, a first end of which is coupled to a first output port of the second coupler; a short optical fiber of length M, a first end of which is coupled to a second output port of the second coupler; a third directional coupler having two input ports, one coupled to a second end of the reference fiber and the other coupled to a second end of the short fiber; and a photodetector coupled to an output port of the third directional coupler.
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Specification