DYNAMIC OPTICAL WAVEGUIDE SENSOR
Methods and apparatuses that sense physical parameters, such as pressure and strain, using optical waveguide sensors are described. A light source emits light at a predetermined wavelength along an optical waveguide having a fiber Bragg grating optical sensing element. That sensing element reflects light in accord with a sloped -shape function of reflected light amplitude verses wavelength. A receiver converts the reflected light into electrical signals and an analyzer then determines a physical parameter based on changes of amplitude of the reflected light. The analyzer also maintains the wavelength of the light such that the wavelength corresponds to a slope wavelength of the shape function.
This application is a divisional of U.S. patent application Ser. No. 11/076,706, filed Mar. 10, 2005, now U.S. Pat. No. 7,302,123, which is herein incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION1. Field of the Invention
Embodiments of the present invention generally relate to optical waveguide sensors, and more particularly to a fiber Bragg grating optical waveguide sensors that dynamically senses strain induced by a stimuli acting upon a transduction mechanism. Description of the Related Art
A fiber Bragg grating (FBG) is an optical element that is formed by a photo-induced periodic modulation of the refractive index of an optical waveguide's core. An FBG element is highly reflective to light having wavelengths within a narrow bandwidth that is centered at a wavelength that is referred to as the Bragg wavelength. Other wavelengths pass through the FBG without reflection. The Bragg wavelength itself is dependent on physical parameters, such as temperature and strain, that impact on the refractive index. Therefore, FBG elements can be used as sensors to measure such parameters. After proper calibration, the Bragg wavelength acts is an absolute measure of the physical parameters.
One way of using fiber Bragg grating elements as sensors is to apply strain from an elastic structure (e.g., a diaphragm, bellows, etc.) to a fiber Bragg grating element. For example, U.S. Pat. No. 6,016,702, issued Jan. 25, 2000, entitled “High Sensitivity Fiber Optic Pressure Sensor for Use in Harsh Environments” by inventor Robert J. Maron discloses an optical waveguide sensor in which a compressible bellows is attached to an optical waveguide at one location while a rigid structure is attached at another. A fiber Bragg grating (FBG) is embedded within the optical waveguide between the compressible bellows and the rigid structure. When an external pressure change compresses the bellows the tension on the fiber Bragg grating is changed, which changes the Bragg wavelength.
Another example of using fiber Bragg grating elements as pressure sensors is presented in U.S. Pat. No. 6,422,084, issued Jul. 23, 2002, entitled “Bragg Grating Pressure Sensor” by Fernald, et al. That patent discloses optical waveguide sensors in which external pressure longitudinally compresses an optical waveguide having one or more fiber Bragg grating. The optical waveguide can be formed into a “dog bone” shape that includes a fiber Bragg grating and that can be formed under tension or compression to tailor the pressure sensing characteristics of the fiber Bragg grating. Another fiber Bragg grating outside of the narrow portion of the dog bone can provide for temperature compensation.
While the foregoing pressure sensing techniques are beneficial, those techniques may not be suitable for all applications. Therefore, fiber Bragg grating techniques suitable for dynamically sensing varying parameters such as pressure and strain would be useful. Also useful would be fiber Bragg grating techniques that provide for both static and dynamic measurements of parameters.
SUMMARY OF THE INVENTIONEmbodiment of the present invention generally provides for optical waveguide measurement techniques that are suitable for sensing dynamically varying physical parameters such as pressure and strain. Furthermore, embodiments of the present invention also provide for both static and dynamic measurements of physical parameters.
The foregoing and other objects, features, and advantages of the present invention will become more apparent in light of the following detailed description of exemplary embodiments thereof.
BRIEF DESCRIPTION OF THE DRAWINGSSo that the manner in which the above recited features of the present invention can be understood in detail, more particular descriptions of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
The present invention provides for optical waveguide measurement systems that are suitable for sensing dynamically varying physical parameters such as pressure and strain. Some embodiments of the present invention enable both static and dynamic measurements of physical parameters. Embodiments of the present invention are suitable for use in harsh environments as found in oil and/or gas wells, engines, combustion chambers, etc.
The foregoing method illustrated with the assistance of
In addition to providing dynamic pressure measurements, the principles of the present invention also provide for determining dynamic (AC) strain. One technique of doing this is illustrated in
Still referring to
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims
1. An optical sensor comprising:
- an optical waveguide with a first fiber Bragg grating having a first Bragg wavelength, a second fiber Bragg grating having a second Bragg wavelength, and a long period grating disposed between said first fiber Bragg grating and said second fiber Bragg grating;
- a light source for emitting light at said first Bragg wavelength and at said second Bragg wavelength;
- a first receiver for converting reflected light at said first Bragg wavelength into first electrical signals;
- a second receiver for converting reflected light at said second Bragg wavelength into second electrical signals;
- a coupler for coupling said light into said optical waveguide, for coupling reflected light at said first Bragg wavelength to said first receiver, and for coupling reflected light at said second Bragg wavelength to said second receiver; and
- an analyzer for receiving said first and said second electrical signals and for using said first and said second electrical signals to determine a physical parameter applied to said long period grating.
2. The optical sensor of claim 1 wherein said physical parameter changes an amplitude of reflected light at said second Bragg wavelength.
3. The optical sensor of claim 2 wherein said physical parameter is stress.
4. The optical sensor of claim 2 wherein said physical parameter is strain.
5. The optical sensor of claim 2 wherein said physical parameter is pressure.
6. The optical sensor of claim 1, further including a filter disposed between said coupler and said first receiver.
Type: Application
Filed: Nov 27, 2007
Publication Date: Apr 10, 2008
Inventor: Richard Jones (Hamden, CT)
Application Number: 11/945,418
International Classification: G02B 6/00 (20060101);