Multi-channel fiber optic sensor system

Claim 2

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.

Claim 3

A data gathering system, including: 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.

Claim 4

A data gathering system, including: 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.

Claim 6

The system of claim 3, wherein: the portion of the first acoustic wave propagating through the interaction portion of the main fiber is a planar acoustic wave having frequency f 1 ; and the portion of the second acoustic wave propagating through the interaction portion of the main fiber is a planar acoustic wave having frequency f 2 , where f 2 is different from f 1 .

Claim 8

The system of claim 5, wherein: the portion of the first acoustic wave propagating through the interaction portion of the main fiber is a planar acoustic wave having frequency f 1 ; and the portion of the second acoustic wave propagating through the interaction portion of the main fiber is a planar acoustic wave also having frequency f 1 , where f 1 =(2nV)/Mλ o (cosine 45°), where n is the optical refractive index of the fiber, V is the velocity of the first acoustic wave in the fiber, λ o is the free space wavelength of the interrogating light signal, and M is a positive odd integer.

Claim 15

A data generating system, including: 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.

Claim 16

A data generating system, including: 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.

Claim 17

A data gathering system, including: 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.

Claim 18

A data gathering system, including: 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.