Multi-channel fiber optic sensor system

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.degree. 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.degree. 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.

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.

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.