Apparatus and method for measuring strain in bragg gratings
First Claim
1. A method for measuring strain of gratings written in an optical fiber comprising the steps of:
- a) providing a reference optical fiber network having a reference optical fiber;
b) transmitting optical radiation over a plurality of contiguous predetermined wavelength ranges into the reference optical fiber network and an optical fiber network under test, the optical fiber network under test including a reflector and a sensing optical fiber having a plurality of gratings written thereon, the transmission of optical radiation over each wavelength range into the reference optical fiber network and the optical fiber network under test producing a plurality of reference interference fringes and measurement interference fringes, respectively;
c) detecting the reference and measurement interference fringes;
d) sampling the detected reference and measurement interference fringes such that each sampled value of the reference and measurement interference fringes is associated with a corresponding sample number;
e) determining for each sample number the wavelength change of the reference optical fiber due to the wavelength of the optical radiation;
f) matching each wavelength change determined in step (e) with a corresponding sampled value of each measurement interference fringe;
g) transforming each sampled measurement interference fringe into a spatial domain waveform such that each spatial domain waveform corresponds to one of the contiguous predetermined wavelength ranges;
h) summing the spatial domain waveforms to form a summation spatial domain waveform;
i) determining from the summation spatial domain waveform the location of each grating with respect to the reflector of the optical fiber network under test;
j) determining from each spatial domain waveform of transforming step (g) a portion of the spatial domain waveform corresponding to a particular grating;
k) transforming each portion determined in step (j) into a corresponding frequency spectrum representation; and
l) determining the strain on the grating at each wavelength of optical radiation by determining the difference between the current wavelength and an earlier, zero-strain wavelength measurement.
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Accused Products
Abstract
An apparatus and method for measuring strain of gratings written into an optical fiber. Optical radiation is transmitted over a plurality of contiguous predetermined wavelength ranges into a reference optical fiber network and an optical fiber network under test to produce a plurality of reference interference fringes and measurement interference fringes, respectively. The reference and measurement fringes are detected and sampled such that each sampled value of the reference and measurement fringes is associated with a corresponding sample number. The wavelength change of the reference optical fiber, for each sample number, due to the wavelength of the optical radiation is determined. Each determined wavelength change is matched with a corresponding sampled value of each measurement fringe. Each sampled measurement fringe of each wavelength sweep is transformed into a spatial domain waveform. The spatial domain waveforms are summed to form a summation spatial domain waveform that is used to determine location of each grating with respect to a reference reflector. A portion of each spatial domain waveform that corresponds to a particular grating is determined and transformed into a corresponding frequency spectrum representation. The strain on the grating at each wavelength of optical radiation is determined by determining the difference between the current wavelength and an earlier, zero-strain wavelength measurement.
243 Citations
30 Claims
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1. A method for measuring strain of gratings written in an optical fiber comprising the steps of:
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a) providing a reference optical fiber network having a reference optical fiber; b) transmitting optical radiation over a plurality of contiguous predetermined wavelength ranges into the reference optical fiber network and an optical fiber network under test, the optical fiber network under test including a reflector and a sensing optical fiber having a plurality of gratings written thereon, the transmission of optical radiation over each wavelength range into the reference optical fiber network and the optical fiber network under test producing a plurality of reference interference fringes and measurement interference fringes, respectively; c) detecting the reference and measurement interference fringes; d) sampling the detected reference and measurement interference fringes such that each sampled value of the reference and measurement interference fringes is associated with a corresponding sample number; e) determining for each sample number the wavelength change of the reference optical fiber due to the wavelength of the optical radiation; f) matching each wavelength change determined in step (e) with a corresponding sampled value of each measurement interference fringe; g) transforming each sampled measurement interference fringe into a spatial domain waveform such that each spatial domain waveform corresponds to one of the contiguous predetermined wavelength ranges; h) summing the spatial domain waveforms to form a summation spatial domain waveform; i) determining from the summation spatial domain waveform the location of each grating with respect to the reflector of the optical fiber network under test; j) determining from each spatial domain waveform of transforming step (g) a portion of the spatial domain waveform corresponding to a particular grating; k) transforming each portion determined in step (j) into a corresponding frequency spectrum representation; and l) determining the strain on the grating at each wavelength of optical radiation by determining the difference between the current wavelength and an earlier, zero-strain wavelength measurement. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An apparatus for measuring strain of gratings written in an optical fiber comprising:
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a reference optical fiber network having a reference optical fiber; a coherent light source for transmitting optical radiation over a plurality of contiguous predetermined wavelength ranges into the reference optical fiber network and an optical fiber network under test, the optical fiber network under test including a reflector and a sensing optical fiber having a plurality of gratings written thereon, the transmission of optical radiation over each wavelength range into the reference optical fiber network and the optical fiber network under test producing a plurality of reference interference fringes and measurement interference fringes, respectively; a detector for detecting the reference and measurement interference fringes; a circuit for sampling the detected reference and measurement interference fringes such that each sampled value of the reference and measurement interference fringes is associated with a corresponding sample number; and a control system for (l) determining for each sample number the wavelength change of the reference optical fiber due to the wavelength of optical radiation, (ii) matching each wavelength change with a corresponding sampled value of each measurement interference fringe, (iii) transforming each sampled measurement interference fringe into a spatial domain waveform such that each spatial domain waveform corresponds to one of the contiguous predetermined wavelength ranges, (iv) summing the spatial domain waveforms to form a summation spatial domain waveform, (v) determining from the summation spatial domain waveform the location of each grating with respect to the reflector of the optical fiber network under test, (vi) determining from each spatial domain waveform the portion of the spatial domain waveform corresponding to a particular grating, (vii) transforming each portion into a frequency spectrum representation, and (viii) determining the strain on the grating at each wavelength of optical radiation by determining the difference between the current wavelength and an earlier, zero-strain wavelength measurement. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. An apparatus for measuring strain of gratings written in an optical fiber comprising:
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a reference optical fiber network having a reference optical fiber; means for transmitting optical radiation over a plurality of contiguous predetermined wavelength ranges into the reference optical fiber network and an optical fiber network under test, the optical fiber network under test including a reflector and a sensing optical fiber having a plurality of gratings written thereon, the transmission of optical radiation over each wavelength range into the reference optical fiber network and the optical fiber network under test producing a plurality of reference interference fringes and measurement reference interference fringes, respectively; means for detecting the reference and measurement interference fringes; means for sampling the detected reference and measurement interference fringes such that each sampled value of the reference and measurement interference fringes is associated with a corresponding sample number; means for determining for each sample number the wavelength change of the reference optical fiber due to the wavelength of the optical radiation; means for matching each determined wavelength change with a corresponding sampled value of each measurement interference fringe; means for transforming each sampled measurement interference fringe into a spatial domain waveform such that each spatial domain waveform corresponds to one of the contiguous predetermined wavelength ranges; means for summing the spatial domain waveforms to form a summation spatial domain waveform; means for determining from the summation spatial domain waveform the location of each grating with respect to the reflector of the optical fiber network under test; means for determining from each spatial domain waveform a portion of the spatial domain waveform corresponding to a particular grating; means for transforming each determined portion into a corresponding frequency spectrum representation; and means for determining the grating at each wavelength of optical radiation by determining the difference between the current wavelength and an earlier, zero-strain wavelength measurement.
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Specification