Distributed fiber optic sensor for locating and identifying remote disturbances

• US 5,355,208 A
• Filed: 06/24/1992
• Issued: 10/11/1994
• Est. Priority Date: 06/24/1992
• Status: Expired due to Fees

• Current Assignee: Mason & Hanger National Incorporated
• Original Assignee: Mason & Hanger National Incorporated
• Inventors: Crawford, Brian B., Robinson, Jeff C., Reil, Jimmy L., Prenovost, Robert J.
• Primary Examiner(s): Turner, Samuel A.
• Application Number:
  US07/903,358
• Time in Patent Office: 839 Days
• Field of Search: 356/345, 356/350, 356/35.5, 250/227.19, 250/227.27
• US Class Current: 356/35.5
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125
• CPC Class Codes: G08B 13/186 using light guides, e.g. optical fibres

Abstract

A distributed fiber optic sensing system for detecting mechanical, acoustic, or ultrasonic disturbances is disclosed. This system is optimized for use as an intrusion detection system in security applications. Light is launched into opposite ends of a sensing fiber loop such that two beams circulate through the loop in opposite directions and then recombine to produce an interference pattern on a photoelectric detector. Disturbances of the sensing fiber loop produce corresponding changes in the interference pattern and thereby the signal level at the detecter. The changes in the electrical signal from the detector are interpreted to provide alarms when the sensing fiber loop is impinged upon by intrusive disturbances, and to provide location of disturbances along the loop. Means are incorporated to decode uniquely coded sonic or ultrasonic signals from personal transmitters borne by authorized personnel approaching the sensing fiber loop. A remotely activated system disturber is affixed to the sensing fiber loop which, when activated by an operator, provides positive confirmation of sensing loop continuity and system operability.

Claims

1. A distributed fiber optic sensor comprising:

a) a first light source for injecting a first beam of light into a fiber;

b) a first optical splitter whose first port is connected to said first light source by an optical fiber, the splitter being effective to divide the first beam into a second and third beam, which second and third beams exit from the second and third ports of said splitter;

c) a first loop of optical fiber having its opposite ends connected to said second and third ports of said first optical splitter, thereby receiving said second and third beams which propagate through said first loop of optical fiber in opposite directions, and which returns said beams to the splitter to be recombined, a portion of the recombined beam exiting from the fourth port of the splitter;

d) a first photoelectric detector connected by a fiber to the fourth port of said first optical splitter, thereby receiving said portion of said recombined beam;

e) a first electronic circuit connected to said first photoelectric detector for amplifying, analyzing, and decoding the electrical output of said first photoelectric detector resulting from changes in the interference intensity of said recombined beam caused by disturbances to said first loop of optical fiber; and

f) mechanical disturbing means, affixed to the fiber of said first loop of optical fiber, for indicating system operability by deliberately agitating said first loop of optical fiber under control from a central system control station, which agitation causes a positive system output if said first optical fiber is unbroken, and causes no response if said first loop of optical fiber is broken.

2. The distributed fiber optic sensor recited in claim 1 wherein said mechanical disturbing means is a piezoelectric element having a portion of said first loop of optical fiber affixed to its surface such that application of an electrical voltage to said piezoelectric element will be effective to change the optical properties of said portion of the fiber sufficient to cause a disturbance in the output of said photoelectric detector.

3. The distributed fiber optic sensor recited in claim 1 wherein said mechanical disturbing means is an electromechanical activator having a current coil surrounding an armature which is effective to impress said armature on said loop of optical fiber when an electrical current is passed through said coil sufficient to cause a disturbance in the output of said photoelectric detector.

4. A distributed fiber optic sensor comprising:

a) a first light source for injecting a first beam of light into a fiber;

b) a first optical splitter whose first port is connected to said first light source by an optical fiber, the splitter being effective to divide the first beam into a second and third beam, which second and third beams exit from the second and third ports of said splitter;

c) a first loop of optical fiber having its opposite ends connected to said second and third ports of said first optical splitter, thereby receiving said second and third beams which propagate through said first loop of optical fiber in opposite directions, and which returns said beams to the splitter to be recombined, a portion of the recombined beam exiting from the fourth port of the splitter;

d) a first photoelectric detector connected by a fiber to the fourth port of said first optical splitter, thereby receiving said portion of said recombined beam;

e) a first electronic circuit connected to said first photoelectric detector for amplifying, analyzing, and decoding the electrical output of said first photoelectric detector resulting from changes in the interference intensity of said recombined beam caused by disturbances to said first loop of optical fiber;

f) sound emitting means, carried on the person of an authorized individual, for transmitting a unique coded signal which is effective to disturb said first loop of optical fiber sufficient to be detected and demodulated by said first electronic circuit; and

g) decoding means for demodulating and interpreting said unique coded signal to identify the authorized individual bearing said sound emitting means.

5. The distributed fiber optic sensor recited in claim 4 wherein said sound emitting means operates within the audible frequency band.

6. The distributed fiber optic sensor recited in claim 4 wherein said sound emitting means operates within the ultrasonic range.

7. A distributed fiber optic sensor comprising:

a) a first light source for injecting a first beam of light into a fiber;

b) a first optical splitter whose first port is connected to said first light source by an optical fiber, the splitter being effective to divide the first beam into a second and third beam, which second and third beams exit from the second and third ports of said splitter;

c) a first loop of optical fiber having its opposite ends connected to said second and third ports of said first optical splitter, thereby receiving said second and third beams which propagate through said first loop of optical fiber in opposite directions, and which returns said beams to the splitter to be recombined, a portion of the recombined beam exiting from the fourth port of the splitter;

d) a first photoelectric detector connected by a fiber to the fourth port of said first optical splitter, thereby receiving said portion of said recombined beam;

e) a first electronic circuit connected to said first photoelectric detector for amplifying, analyzing, and decoding the electrical output of said first photoelectric detector resulting from changes in the interference intensity of said recombined beam caused by disturbances to said first loop of optical fiber;

f) spectral analysis means for determining the spectral content of said electrical output in real time as said electrical output occurs;

g) signal processing and computing means for identifying origin of said electrical output by comparisons of amplitude and spectral content to patterns of known past events; and

h) computer self-programming means for automatically refining and updating stored repertoire of known patterns by analysis of current event signals.

8. A distributed fiber optic sensor comprising:

a) a first light source for injecting a first beam of light into a fiber;

b) a first optical splitter whose first port is connected to said first light source by an optical fiber, the splitter being effective to divide the first beam into a second and third beam, which second and third beams exit from the second and third ports of said splitter;

c) a first loop of optical fiber having its opposite ends connected to said second and third ports of said first optical splitter, thereby receiving said second and third beams which propagate through said first loop of optical fiber in opposite directions, and which returns said beams to the splitter to be recombined, a portion of the recombined beam exiting from the fourth port of the splitter;

d) a first photoelectric detector connected by a fiber to the fourth port of said first optical splitter, thereby receiving said portion of said recombined beam;

e) a first electronic circuit connected to said first photoelectric detector for amplifying, analyzing, and decoding the electrical output of said first photoelectric detector resulting from changes in the interference intensity of said recombined beam caused by disturbances to said first loop of optical fiber;

f) a second light source for injecting a fourth beam of light into a fiber;

g) a second optical splitter whose first port is connected to said second light source by an optical fiber, the splitter being effective to divide the fourth beam into a fifth and sixth beam, which fifth and sixth beams exit from the second and third ports of the splitter;

h) a second loop of optical fiber overlaid on and contiguous to said first loop of optical fiber, having its opposite ends connected to said second and third ports of said second optical splitter, thereby receiving said fifth and sixth beams which propagate through said second loop of optical fiber in opposite directions, and which returns said beams to the splitter to be recombined, a portion of the recombined beam exiting from the fourth port of the splitter;

i) a second photoelectric detector connected by a fiber to the fourth port of said second optical splitter, thereby receiving said portion of said recombined beams;

j) a second electronic circuit connected to said second photoelectric detector for amplifying, analyzing, and decoding the electrical output of said second photoelectric detector resulting from changes in the interference intensity of said recombined beam caused by disturbances to said second loop of optical fiber;

k) a first triggering means connected to said first photoelectric detector for producing a timing pulse when the leading edge of a signal from said first loop of optical fiber caused by a common disturbance exceeds a pre-set threshold value;

l) a second triggering means connected to said second photoelectric detector for producing a timing pulse when the leading edge of a signal from said second loop of optical fiber caused by said common disturbance impact exceeds a pre-set threshold value;

said first optical splitter, and associated first photoelectric detector, first electronic circuit and first triggering means being located at a distance apart around the overlaid portions of the first and second optical fiber loops from said second optical splitter, and associated second photoelectric detector, second electronic circuit, and second triggering means such that a measurable difference in elapsed time will occur between the arrival of the leading edge of a signal from said first loop of optical fiber at said first triggering means and the arrival of the leading edge of a corresponding signal from said second loop of optical fiber at said second triggering means caused by a common disturbance of both fiber loops at a common point.

m) time measuring means for measuring the elapsed time between arrival of the timing pulse from said first triggering means and the timing pulse from said second triggering means; and

n) computing means connected to said time measuring means for calculating position of said common disturbance along said first and second loops of optical fiber based on said elapsed time.

9. The distributed fiber optic sensor recited in claim 8 further comprising:

a) remote transmission means providing the link between said second triggering means and said time measuring means; and

b) time delay means for delaying pulse from said first triggering means to said time measuring means by an amount equal to the propagation time over said remote transmission means.

10. The distributed fiber optic sensor recited in claim 8 further comprising:

a) remote transmission means providing the link between said first triggering means and said time measuring means; and

b) time delay means for delaying pulse from said second triggering means to said time measuring means by an amount equal to the propagation time over said remote transmission means.