Apparatus for sensing temperature and/or strain in an object with optical fiber Bragg gratings

• US 6,018,160 A
• Filed: 03/19/1998
• Issued: 01/25/2000
• Est. Priority Date: 03/22/1997
• Status: Expired due to Term

• Current Assignee: BAE Systems Plc
• Original Assignee: British Aerospace, Inc. (BAE Systems Plc)
• Inventors: Zhang, Lin, Bennion, Ian
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/040,936
• Time in Patent Office: 677 Days
• Field of Search: 250/227.14, 250/227.16, 250/227.19, 385/12, 385/13, 356/5.12, 356/5.13, 356/32, 356/35, 340/555-557
• US Class Current: 250/227.14
• CPC Class Codes: G01B 11/16 for measuring the deformation in a solid, e.g. optical strain gauge
• CPC Class Codes: G01D 5/35316 using a Bragg gratings
• CPC Class Codes: G01K 5/52 with electrical conversion means for final indication
• CPC Class Codes: G01L 1/24 by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet

Abstract

Apparatus for sensing temperature and/or strain in an object includes a broadband light source (1), connector means (2) in the form of an optical circulator or an optical coupler to which at least two substantially identical optical fiber Bragg gratings (4, 5) are connected. Grating (4) receives the broadband light from the connector means (2) and functions as a sensor of temperature and/or strain in an object. Light is reflected back from the grating (4) to the connector means (2) and then passed to the grating (5) which acts as a reference grating through which a light output signal is transmitted to a detector (8) which is conveniently a photodetector. Means are provided for chirping the two gratings (4, 5) at the same bandwidth and the detector (8) measures the intensity of the received light output signal, with the intensity being monotonically related to the change in temperature and/or strain sensed by the grating (4) in the object.

Claims

1. Apparatus for sensing temperature and/or strain in an object, including a source of broadband light, connector means for receiving a beam of broadband light from the source at least two substantially identical optical Fiber Bragg gratings, a first of which gratings is operable to receive the broadband light beam from the connector means and function as a sensor of temperature and/or strain on the object when attached to or forming part of the object, by reflecting part of the received light beam back to the connector means, and a second of which gratings is operable to receive from the connector means the reflected light beam part and function as a reference grating through which a light output signal is transmitted, means for chirping said at least two gratings at the same band width, and a detector for receiving the light output signal and measuring the intensity of said light output signal, which intensity is monotonically related to the change in temperature and/or strain sensed in the object.

2. Apparatus according to claim 1, including optical fibres for transmitting light between the source, connector means, said at least two gratings and the detector.

3. Apparatus according to claim 1, wherein the source of broadband light is a fluorescent light source.

4. Apparatus according to claim 3, wherein each grating is a Boron/Germania co-doped optical fibre subjected to a two-beam transverse interferometric exposure by ultraviolet light from a continuous wave frequency-doubled argon laser.

5. Apparatus according to claim 1, wherein the means for chirping said at least two gratings operates at dissimilar interfering wave fronts.

6. Apparatus according to claim 1, wherein the detector is a photodiode.

7. Apparatus according to claim 1, wherein the connector means is an optical circulator having at least three ports.

8. Apparatus according to claim 1, wherein the connector means is an optical coupler having at least three ports.