Optical sensing apparatus and method

• US 4,443,700 A
• Filed: 05/13/1982
• Issued: 04/17/1984
• Est. Priority Date: 02/01/1980
• Status: Expired due to Fees

• Current Assignee: Pedro B. Macedo, Theodore A. Litovitz
• Original Assignee: Pedro B. Macedo, Theodore A. Litovitz
• Inventors: Lagakos, Nicholas, Mohr, Robert K., Macedo, Pedro B., Litovitz, Theodore A., Meister, Robert
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Hostetter, Darwin R.
• Application Number:
  US06/377,904
• Time in Patent Office: 705 Days
• Field of Search: 250/227, 73/705, 350/96.15, 350/96.29
• US Class Current: 250/227.16
• CPC Class Codes: G01B 11/18 using photoelastic elements
• CPC Class Codes: G01D 5/26 characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
• CPC Class Codes: G01K 1/024 for remote indication
• CPC Class Codes: G01L 11/025 using a pressure-sensitive optical fibre
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: G02B 6/2852 using tapping light guides arranged sidewardly, e.g. in a non-parallel relationship with respect to the bus light guides (light extraction or launching through cladding, with or without surface discontinuities, bent structures)

Abstract

A sensor for measuring stress, temperature, pressure, sound, etc. comprising an optical waveguide, preferably an optical fiber waveguide, a light source which injects light into one end of the waveguide, a deformer contacting and deforming the waveguide to cause light to couple from originally excited modes to other modes, and an optical detector to detect the change in light coupling caused by deformation of the waveguide.

Claims

1. A sensor comprising an optical waveguide having means for transmitting light in at least two groups of modes denoted A and B, a pulsed optical light source means for injecting light into said waveguide so that light transmitted at least initially along said waveguide will be substantially in one of said groups, deformer means responsive to an external stress for deforming more than one spaced apart region of said waveguide with such deformation being effective to change the character of the transmission of at least a portion of the light in the vicinity of the deformation from said one group to the said other group of modes, and an optical detector having means to detect a change in the light in one of said groups in more than one of said regions and thereby monitor said external stress and separate the light from different regions by a time delay introduced because of the spatial separation between regions.

2. The sensor as claimed in claim 1 wherein said waveguide comprises one or more inter-connected optical fiber waveguides extending from said light sources and including each of said regions.

3. The sensor as claimed in claim 1 wherein a plurality of optical detectors are provided.

4. The sensor as claimed in claim 3 wherein said waveguide comprises an optical fiber extending from said light source and including each of said regions.

5. The sensor as claimed in claim 1 wherein one of said deformer means is sensitive to pressure and the other of said deformer means is sensitive to temperature.

6. A method comprising injecting pulsed light into an optical waveguide having at least two groups of modes A and B each group containing at least one mode, deforming more than one spaced apart region of the waveguide by application of an external stress, the deformation producing a change in the coupling of light between A modes and B modes, the deformation producing a change in the light power in one of said groups which change is a function of the change in said external stress, and optically detecting a change in said light in one of said groups in more than one of said regions and thereby monitoring said external stress and separate the light from different regions by a time delay introduced because of the spatial separation between regions.

7. A sensor as claimed in claim 6 further comprising a plurality of pressure sensitive enclosures with a said pressure sensitive enclosure connected to a said deformer means so that a change in pressure at each enclosure causes a change in deformation of said regions of said waveguide whereby said sensor measures pressure at each said region.

8. A sensor according to claim 7 further comprising a low frequency pressure transmitting device extending through the wall of at least one of said enclosures and which allows the pressure inside the enclosure to be essentially equilibrated with low frequency components of the pressure external to the enclosure so that the change in deformation of the waveguide is determined only by high frequency components of said external pressure.

9. The sensor as claimed in claim 8 wherein said low frequency components are less than one Hertz, and said high frequency components are greater than 20 Hertz.

10. The sensor as claimed in claim 7 wherein said pressure sensitive enclosure is a hydrophone.

11. A sensor as claimed in claim 6 wherein at least one of said deformer means comprises at least two materials having dissimilar thermal expansion coefficients and arranged to cause a change in deformation of said region of said waveguide upon a change in temperature whereby said sensor is used to measure temperature.