Fiber optic sensor

• US 4,488,040 A
• Filed: 11/19/1982
• Issued: 12/11/1984
• Est. Priority Date: 11/19/1982
• Status: Expired due to Term

• Current Assignee: GTE Government Systems Corporation (General Dynamics Corporation)
• Original Assignee: GTE Products Corporation (Ams-Osram AG)
• Inventors: Rowe, Donald H.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Gonz/a/ lez, Frank
• Application Number:
  US06/442,984
• Time in Patent Office: 753 Days
• Field of Search: 250/227, 250/231 R, 350/96.23, 350/96.29, 350/96.30
• US Class Current: 250/227.14
• CPC Class Codes: G01L 1/245 using microbending
• CPC Class Codes: G08B 13/126 for a housing, e.g. a box, a safe, or a room

Abstract

A fiber optic sensor useful, for example, in intrusion detection systems for sensing seismic or pressure disturbances produced by an intruder, comprises a cable having an optical fiber core for transmitting the output of a laser, a hard preferably electrically nonconductive strand wound helically on and coextensive with the fiber, and a compliant tubular sleeve over the fiber and strand. The coils of the strand are axially spaced apart and circumferentially engage the fiber. The sleeve fits snugly over the strand and fiber and transmits through the strand coils to the fiber forces resulting from disturbances to be detected, subjecting the fiber to bending stresses. With cable connected at one end to the laser output, the polarization of light transmitted by the fiber is changed by the induced stresses and is detected at the other end of the cable to indicate the occurrence of the disturbance.

Claims

1. An optical fiber sensor cable responsive to forces applied transversely of the cable for changing the light transmission characteristics of the cable, comprising

an elongated optical fiber,

a strand wound around and in engagement with the exterior of said fiber with adjacent coils of the strand axially spaced apart, said strand being characterized by a hardness sufficient to apply a bending stress to said fiber in response to transverse forces applied to said cable, and

a compliant sleeve covering said strand-wound fiber and engaging said strand only at the intersection of the latter with a longitudinal plane through said fiber whereby only forces in said plane and applied to said sleeve are conducted by said strand to said fiber.

2. A force detection system comprising

a laser,

an optical sensor cable connected at one end to said laser for transmitting light therefrom,

means to apply a transverse force to said cable whereby to change the characteristics of light transmitted by said cable, and

optical detecting means connected to the other end of said cable and responsive to changes in said light characteristics for indicating the application of said force to said cable,

said cable comprising an elongated optical fiber,

a hard strand helically wound about said fiber over the length thereof, and

a compliant sleeve disposed around and coextensive with said fiber and said strand with the interior of said sleeve engaging only parts of said strand intersected by a single longitudinal plane through said cable whereby said fiber is responsive only to unidirectional radial forces in said plane.

3. The system according to claim 2 in which the cross-sectional shape of said sleeve is oblong, said fiber being responsive only to forces applied to the exterior of said sleeve in the direction of the minimum transverse dimension thereof.