Optical sensing device containing fiber bragg gratings
First Claim
1. A device for measuring a change in an environment comprising:
- a first optical fiber having a plurality of fiber Bragg gratings, wherein each of the fiber Bragg gratings has a different predetermined reflection wavelength;
a broadband light source optically coupled to the optical fiber;
a scanning filter optically coupled to optical fiber;
an interferometer optically coupled to the scanning filter;
a first photodetector generating a first output, wherein the first photodetector is optically coupled to the interferometer;
a second photodetector generating a second output, wherein the second photodetector is optically coupled to the interferometer; and
a third photodetector generating a third output, wherein the third photodetector is optically coupled to the interferometer.
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Abstract
A new optical sensing device containing fiber Bragg gratings, a scanning bandpass filter, an interferometer and multiple photodetectors is disclosed. The present invention also describes a new system and method for fibre Bragg grating (FBG) sensor interrogation and multiplexing. The new system combines a scanning Fabry-Perot (SFP) bandpass filter used to wavelength-multiplex multiple gratings in a single fiber, and an unbalanced Mach-Zehnder fibre interferometer made with a 3×3 coupler to detect strain-induced wavelength shifts. A passive technique for interferometer drift compensation using non-sensing FBGs is included in the system. A complete prototype system interrogates four gratings in a single fiber at a Nyquist sampling rate up to 10 kHz, with a noise floor measured near 4 nε Hz−½ above 0.1 Hz. The inclusion of the interferometer drift compensation technique is shown to make quasi-static measurements feasible.
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Citations
26 Claims
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1. A device for measuring a change in an environment comprising:
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a first optical fiber having a plurality of fiber Bragg gratings, wherein each of the fiber Bragg gratings has a different predetermined reflection wavelength;
a broadband light source optically coupled to the optical fiber;
a scanning filter optically coupled to optical fiber;
an interferometer optically coupled to the scanning filter;
a first photodetector generating a first output, wherein the first photodetector is optically coupled to the interferometer;
a second photodetector generating a second output, wherein the second photodetector is optically coupled to the interferometer; and
a third photodetector generating a third output, wherein the third photodetector is optically coupled to the interferometer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An interrogating system for a fiber optical sensor having fiber Bragg gratings comprising:
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a scanning filter optically coupled to the fiber optical sensor;
an interferometer optically coupled to the output port of the scanning filter;
a first photodetector optically coupled to the interferometer;
a second photodetector optically coupled to the interferometer; and
a third photodetector optically coupled to the interferometer. - View Dependent Claims (12, 13, 14, 15, 17, 18, 19)
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16. A method for measuring a change in an environment comprising the steps of:
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irradiating a fiber having a plurality of fiber Bragg gratings with different center wavelengths with a broadband light to generate a reflected light from each of the Bragg gratings, wherein each of the reflected lights is reflected from a specific fiber Bragg grating and has a wavelength which is the sum of the center wavelength characteristic of the specific fiber Bragg grating and a wavelength shift based on the change in the environment;
filtering one of the reflected lights through the scanning filter at a time;
encoding the wavelength of the reflected light from the scanning filter into a phase signal embedded in at least three interference lights using an interferometer;
converting the at least three interference lights into at least three voltage signals using at least three photodetectors;
demodulating the at least three voltage signals to obtain the phase of the phase signal;
calculating the wavelength shift of the transmitted light from the phase of the phase signal; and
determining the change in the environment from the wavelength shift.
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20. A demodulating unit for processing outputs from an interrogation system for an optical sensing device having fiber Bragg gratings comprising:
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means for determining a tangent of a phase of a reflected light from one of the fiber Bragg gratings from the reflected light passing through the interrogation system;
means for determining an arctangent of the tangent of the phase of the reflected light; and
means for phase-unwrapping the arctangent to obtain the phase of the transmitted light. - View Dependent Claims (21, 22, 23, 25, 26)
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24. A method for processing outputs from an interrogation system for an optical sensing device having fiber Bragg gratings comprising the steps of:
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determining a tangent of a phase of a phase signal using the outputs from the interrogating system;
determining an arctangent of the tangent of the phase of the phase signal; and
phase-unwrapping the arctangent.
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Specification