Fiber optic microbending sensor arrays including microbend sensors sensitive over different bands of wavelengths of light

• US 5,118,931 A
• Filed: 09/07/1990
• Issued: 06/02/1992
• Est. Priority Date: 09/07/1990
• Status: Expired due to Term

• Current Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Original Assignee: Mcdonnell Douglas Corporation (The Boeing Co.)
• Inventors: Udd, Eric, Theriault, John P.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): Lee, John R.
• Application Number:
  US07/578,381
• Time in Patent Office: 634 Days
• Field of Search: 250/227.14, 250/227.15, 250/227.16, 250/227.18, 250/227.23, 250/227.24, 250/227.28, 250/226
• US Class Current: 250/227.16
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01L 1/245 using microbending
• CPC Class Codes: G01L 1/246 using integrated gratings, e.g. Bragg gratings
• CPC Class Codes: G01M 11/083 by using an optical fiber in contact with the device under test [DUT]
• CPC Class Codes: G01M 11/3127 using multiple or wavelength variable input source

Abstract

A fiber optic sensing system detects changes in a material based upon physical deformation of a fiber bonded to the structure in which stress, strain or failure is to be detected. Deformation of the fiber affects propagation of light therethrough, permitting detection based upon detected changes in light throughput.

Claims

1. A fiber optic strain sensor, comprising:

a broadband light source producing a beam of light;

a fiber optic beamsplitter having a first port connected to the light source, a second port connected to a wavelength division demultiplexer, and a third port;

a plurality of microbend sensors and associated downstream mirror means each preferentially reflective to a different narrow bandwidth of wavelengths of light in optical communication with said third port of said beamsplitter, each of said microbend sensors and their associated mirror means having an optical sensitivity to strain over one of the different bandwidths;

said wavelength division demultiplexer having its input connected to the second port of the beamsplitter, comprising a plurality of narrow band pass optical filters connected to said input and each of whose outputs will contain one of the different bandwidths from the plurality of mirror means; and

a plurality of optical detectors, each in optical communication with the output of one of the optical filters.

2. The fiber optic strain sensor of claim 1 wherein said light source comprises a superradiant diode.

3. The fiber optic strain sensor of claim 1 wherein said light source comprises a light emitting diode.

4. The optic strain sensor of claim 1 further comprising a depolarizing element, in optical connection between said broadband light source and said first port of said wavelength division demultiplexer.

5. The strain sensor of claim 1 wherein the plurality of microbend sensors and associated downstream mirror means are connected in series to one another.

6. The strain sensor of claim 1 wherein each or the mirror means comprises a series of linear grooves formed in the perimeter of the fiber so as to form a grating selectively reflective to one of the different narrow bandwidths of light.