Microbend optic sensor with fiber being sewn thereto in a sinuously looped disposition

• US 5,134,281 A
• Filed: 12/21/1990
• Issued: 07/28/1992
• Est. Priority Date: 01/31/1990
• Status: Expired due to Fees

• Current Assignee: BryTech., Inc.
• Original Assignee: E L Bryenton & Associates Incorporated
• Inventors: Bryenton, Earl L., Stoffels, Menno, Johnson, Frank, Bryenton, Alan L.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): LE, QUE TAN
• Application Number:
  US07/631,871
• Time in Patent Office: 585 Days
• Field of Search: 250/227.16, 250/227.14, 250/227.24, 250/229, 250/231.1, 250/231.19, 128/748, 128/675, 73/705
• US Class Current: 250/227.16
• CPC Class Codes: A61B 2562/0266 Optical strain gauges
• CPC Class Codes: A61B 5/1073 Measuring volume, e.g. of limbs
• CPC Class Codes: A61B 5/1126 using a particular sensing technique
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion
• CPC Class Codes: G01B 11/18 using photoelastic elements
• CPC Class Codes: G01D 5/35374 Particular layout of the fiber
• 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: G01L 1/243 using means for applying force perpendicular to the fibre axis
• CPC Class Codes: G01L 1/245 using microbending
• CPC Class Codes: G01M 11/083 by using an optical fiber in contact with the device under test [DUT]

Abstract

An optical sensor comprising an optical fiber having a core covered by a cladding, the cladding having an index of refraction different from that of the core, apparatus for retaining the fiber in a sinuously looped disposition, apparatus for fixing the fiber to an object to be sensed whereby movement to be sensed results in one or both of accordion expansion and contraction of loops of the fiber and microbending of the fiber, apparatus for applying a first optical signal into one end of the fiber, apparatus for detecting a resulting optical signal from the other end of the fiber, and apparatus for comparing the first and resulting optical signals to obtain an indication of the movement.

Claims

1. An optical sensor comprising an optical fiber having a core covered by a cladding, the cladding having an index of refraction different from that of the core, means for retaining the fiber in a sinuously looped disposition, means for fixing the fiber and retaining means to an object to be sensed whereby movement to be sensed results in one or both of accordion expansion and contraction of loops of the fiber and microbending of the fiber, the retaining means being comprised of an elastic cloth strip, the fiber being sewn thereto in said sinuously looped disposition, means for applying a first optical signal into one end of the fiber, means for detecting a resulting optical signal from he other end of the fiber, means for comparing the first and resulting optical signals to obtain an indication of said movement, the fiber being loped back upon itself so as to form a first portion and a looped-back portion, both portions of the fiber being disposed so as to follow the same path.

2. An optical fiber as defined in claim 1 in which loops have predetermined maximum smallest radius relative to the fiber diameter which are sufficiently small so as to obtain significant microbending loss thereat.

3. An optical sensor as defined in claim 1 in which the fiber has a diameter of about 100 microns, and the radius of each loop is no greater than about 4 mm.

4. An optical sensor as defined in claim 2 in which the fiber has a diameter of about 250 microns, and the radius of each loop is no greater than about 8 mm.

5. An optical sensor as defined in claim 1 in the form of a belt.

6. An optical sensor as defined in claim 1 having a length at least 20 times the physical amplitude of the loops.

7. An optical sensor comprising an optical fiber having a core covered by a cladding, the cladding having an index of refraction different from that of the core, means for retaining the fiber in a sinuously looped disposition, means for fixing the fiber and retaining means to an object to be sensed whereby movement to be sensed results in one or both of accordion expansion and contraction of loops of the fiber and microbending of the fiber, the retaining means being comprised of an elastic cloth strip, the fiber being sewn thereto in said sinuously looped disposition, means for applying a first optical signal into one end of the fiber, means for detecting a resulting optical signal from the other end of the fiber, means for comparing the first and resulting optical signals to obtain an indication of said movement, various loops of fiber having different radii, to produce variable sensitivity thereof with expansion or contraction of the sensor.