Ofdr device and ofdr method

Patent metadata

Field	Value
Publication number	US-2016245643-A1
Application number	US-201615042616-A
Country	US
Kind code	A1
Filing date	Feb 12, 2016
Priority date	Feb 20, 2015
Publication date	Aug 25, 2016
Grant date	—

Abstract

To provide an OFDR device and an OFDR method capable of measuring a large strain distribution or a large temperature distribution within a narrow measured wavelength range by using an FBG. A measured optical fiber 13 includes a plurality of gratings that is overlappingly formed in order to reflect a plurality of different wavelengths. An OFDR device 1 measures a strain distribution or a temperature distribution of the measured optical fiber 13 on the basis of the result of detection by a measuring range non-inclusion detector 26 that detects gratings of the plurality of gratings of which the reflected wavelengths are not included in the measured wavelength range from the peak wavelengths detected by a peak wavelength detector on the basis of measured wavelength range non-inclusion detecting condition data (Ds) in which a predetermined measured wavelength range is set in the direction of the axis of the peak wavelengths.

First claim

What is claimed is:

1 . An OFDR device that measures a strain distribution or a temperature distribution of a measured optical fiber, the device comprising:
a light source that outputs wavelength-swept light; a measured optical fiber that includes a fiber Bragg grating unit; an optical splitter/combiner that inputs part of output light from the light source to the measured optical fiber and combines reflected light from the measured optical fiber and part of output light from the light source; an optical receiver that converts light from the optical splitter/combiner into an electrical signal; an A/D converter that converts the electrical signal into a digital signal; a spectrogram calculator that calculates a spectrogram by performing discrete Fourier transform on the digital signal; and a peak wavelength detector that detects one or more peak wavelengths of the spectrogram on a wavelength axis, wherein the fiber Bragg grating unit includes a plurality of gratings that is overlappingly formed in order to reflect a plurality of different wavelengths, the OFDR device further includes a measuring range non-inclusion detector that detects gratings of the plurality of gratings of which the reflected wavelengths are not included in the measured wavelength range from the peak wavelengths detected by the peak wavelength detector on the basis of measured wavelength range non-inclusion detecting condition data (Ds) in which a predetermined measured wavelength range is set in the direction of the wavelength axis of the peak wavelengths, and a strain distribution or a temperature distribution of the measured optical fiber is measured on the basis of results from the measuring range non-inclusion detector and the peak wavelengths detected by the peak wavelength detector.

2 . The OFDR device according to claim 1 ,
wherein the measured wavelength range non-inclusion detecting condition data (Ds) is set on the basis of a peak wavelength change in the plurality of gratings with respect to a strain or temperature change in the measured optical fiber and of strain or temperature change ranges that are formed in plural quantities in the direction of a strain or temperature change axis by dividing a strain or temperature change measurable range and are defined by the measured wavelength range and the peak wavelength change in the plurality of gratings, the measuring range non-inclusion detector detects a strain or temperature change range of the plurality of strain or temperature change ranges that includes a strain or temperature of the measured optical fiber from the peak wavelengths detected by the peak wavelength detector on the basis of the measured wavelength range non-inclusion detecting condition data (Ds), and a strain distribution or a temperature distribution of the measured optical fiber is measured on the basis of the strain or temperature change range detected by the measuring range non-inclusion detector and the peak wavelengths detected by the peak wavelength detector.

3 . The OFDR device according to claim 2 , further comprising:
a peak wavelength corrector that determines, when the measuring range non-inclusion detector detects a reflected wavelength of at least one grating of the fiber Bragg grating unit not being included in the measured wavelength range, whether a measurement processing wavelength which is preset to detect a strain or temperature change is included in the peak wavelengths of the gratings of the fiber Bragg grating unit within the measured wavelength range and, if the measurement processing wavelength is not included in the peak wavelengths of the gratings of the fiber Bragg grating unit within the measured wavelength range, converts one or more peak wavelengths of the gratings of the fiber Bragg grating unit within the measured wavelength range into the measurement processing wavelength and outputs the measurement processing wavelength.

4 . The OFDR device according to claim 1 ,
wherein the fiber Bragg grating unit of the measured optical fiber includes two gratings that are overlappingly formed, a space between reflected wavelengths of the two gratings being set to ½ or less of the measured wavelength range, and the measuring range non-inclusion detector detects the number of peak wavelengths detected by the peak wavelength detector, determines that the reflected wavelengths of the two gratings are included in the measured wavelength range if the number of peak wavelengths detected is two, determines that the reflected wavelength of the long wavelength side grating is not included in the measured wavelength range if there is one detected peak wavelength that is on a long wavelength side from the middle of the measured wavelength range, and determines that the reflected wavelength of the short wavelength side grating is not included in the measured wavelength range if there is one detected peak wavelength that is on a short wavelength side from the middle of the measured wavelength range.

5 . The OFDR device according to claim 2 ,
wherein the fiber Bragg grating unit of the measured optical fiber includes two gratings that are overlappingly formed, a space between reflected wavelengths of the two gratings being set to ½ or less of the measured wavelength range, and the measuring range non-inclusion detector detects the number of peak wavelengths detected by the peak wavelength detector, determines that the reflected wavelengths of the two gratings are included in the measured wavelength range if the number of peak wavelengths detected is two, determines that the reflected wavelength of the long wavelength side grating is not included in the measured wavelength range if there is one detected peak wavelength that is on a long wavelength side from the middle of the measured wavelength range, and determines that the reflected wavelength of the short wavelength side grating is not included in the measured wavelength range if there is one detected peak wavelength that is on a short wavelength side from the middle of the measured wavelength range.

6 . The OFDR device according to claim 2 ,
wherein the fiber Bragg grating unit of the measured optical fiber includes three or more gratings that are overlappingly formed, spaces between adjacent reflected wavelengths of the three or more gratings being set to different values, and the measuring range non-inclusion detector estimates gratings of the three or more gratings of which the reflected wavelengths are not included in the measured wavelength range on the basis of one or more spaces between the peak wavelengths detected by the peak wavelength detector.

7 . The OFDR device according to claim 2 ,
wherein the fiber Bragg grating unit of the measured optical fiber includes two or more gratings that are overlappingly formed, reflectances of the two or more gratings being set to different values, and the measuring range non-inclusion detector estimates gratings of the two or more gratings of which the reflected wavelengths are not included in the measured wavelength range on the basis of one or more intensities of the peak wavelengths detected by the peak wavelength detector.

8 . The OFDR device according to claim 6 ,
wherein the fiber Bragg grating unit of the measured optical fiber includes n (n≧3) gratings that are overlappingly formed, spaces between adjacent reflected wavelengths of the n gratings being set to different values, a difference between a longest reflected wavelength and a shortest reflected wavelength of the reflected wavelengths being set to (n−1)/2 times the measured wavelength range or less, the peak wavelength detector detects peak wavelengths of two gratings of the n gratings, and the measuring range non-inclusion detector estimates gratings of

Assignees

• Anritsu Corp

Inventors

• Mori Takashi

Classifications

• G01B11/16 Primary

  for measuring the deformation in a solid, e.g. optical strain gauge · CPC title

• G01K11/32 Primary

  using changes in transmittance, scattering or luminescence in optical fibres · CPC title

• G01M11/3172

  Reflectometers detecting the back-scattered light in the frequency-domain, e.g. OFDR, FMCW, heterodyne detection · CPC title

• G01B11/18 Primary

  using photoelastic elements · CPC title

• G01K11/3206

  at discrete locations in the fibre, e.g. using Bragg scattering · CPC title