Optical interrogator for performing interferometry using Bragg gratings

Patent metadata

Field	Value
Publication number	US-11054288-B2
Application number	US-201916523864-A
Country	US
Kind code	B2
Filing date	Jul 26, 2019
Priority date	Dec 4, 2014
Publication date	Jul 6, 2021
Grant date	Jul 6, 2021

Abstract

An optical fiber interrogator for interrogating optical fiber that includes fiber Bragg gratings (“FBGs”). The interrogator includes a light source operable to emit phase coherent light, amplitude modulation circuitry optically coupled to the light source and operable to generate pulses from the light, and control circuitry communicatively coupled to the amplitude modulation circuitry that is configured to perform a method for interrogating the optical fiber. The method includes generating a pair of light pulses by using the amplitude modulation circuitry to modulate light output by the light source without splitting the light.

First claim

We claim:

1. A method for interrogating optical fiber comprising fiber Bragg gratings (“FBGs”), the method comprising:
(a) generating a first pair of light pulses and a second pair of light pulses from phase coherent light emitted from a light source, wherein the light pulses are generated by modulating the intensity of the light without splitting the light, and wherein the second pair of light pulses immediately follows the first pair of light pulses;
(b) for each of the first and second pairs of light pulses, applying a phase shift to at least one of the light pulses in the pair relative to the other of the light pulses in the pair, wherein the phase shift applied to the at least one of the light pulses in the first pair of light pulses and the phase shift applied to the at least one of the light pulses in the second pair of light pulses are the same;
(c) transmitting the light pulses along the optical fiber;
(d) receiving reflections of the pulses off the FBGs; and
(e) determining whether an optical path length between the FBGs has changed from an interference pattern resulting from the reflections of the pulses.

2. The method of claim 1 wherein determining whether the optical path length has changed comprises converting the interference pattern from an optical to an electrical signal.

3. The method of claim 1 wherein a phase modulator is used to phase shift the at least one of the light pulses, the phase modulator selected from the group consisting of a lithium niobate phase modulator, a gallium arsenide phase modulator, and an indium phosphide phase modulator.

4. The method of claim 1 wherein polarization of the light pulses is maintained from when the light pulses are generated until the light pulses are transmitted along the optical fiber.

5. The method of claim 4 further comprising splitting the polarization of the reflected pulses prior to converting the interference patterns.

6. The method of claim 1 wherein polarization of the light pulses is maintained from when the light pulses are generated until the interference pattern resulting from the reflections of the pulses is observed.

7. The method of claim 1 wherein the light source is a laser and the intensity of the light is modulated using a first optical amplifier external of and optically coupled to the laser.

8. The method of claim 1 wherein the light is generated by an electroabsorption modulated laser and the intensity of the light is modulated using an absorption region comprising part of the laser.

9. The method of claim 1 wherein the light source comprises a laser having a power of at least 100 mW.

10. The method of claim 1 wherein the applying the phase shift comprises applying a positive phase shift to a first pulse and applying a negative phase shift to a subsequent, second pulse intended to interfere with the first pulse.

11. The method of claim 10 wherein the first and second pulses differ in phase from each other by more than π radians.

12. The method of claim 10 , wherein a magnitude of the positive phase shift is equal to a magnitude of the negative phase shift.

13. The method of claim 1 further comprising:
(a) transmitting a calibration pulse to the FBGs;
(b) receiving reflections of the calibration pulse off the FBGs; and
(c) based on differences in when the reflections of the calibration pulse are received, determining timing between the sensing and reference pulses.

14. The method of claim 1 wherein applying the phase shift comprises applying a non-linear phase shift or a piecewise linear phase shift to the at least one of the pulses.

15. The method of claim 14 wherein the phase shift is a Barker code.

16. The method of claim 1 further comprising dithering leakage from the light source by phase shifting the leakage between 0 and it radians at a frequency at least 2.5 times higher than a frequency at which interrogation is being performed.

17. An optical fiber interrogator for interrogating at least two optical fibers comprising fiber Bragg gratings (“FBGs”), the interrogator comprising:
(a) a light source operable to emit phase coherent light;
(b) amplitude modulation circuitry optically coupled to the light source and operable to generate pulses from the light, wherein the pulses are generated without splitting the light;
(c) an optical switch optically coupled to the light source and comprising at least two output channels including a first output channel and a second output channel, the optical switch operable to switch transmission of light between each of the at least two output channels;
(d) control circuitry, communicatively coupled to the amplitude modulation circuitry and to the optical switch, configured to perform a method for interrogating each of the at least two optical fibers comprising generating first and second pairs of light pulses for the first output channel, and third and fourth pairs of light pulses for the second output channel, by using the amplitude modulation circuitry to modulate light output by the light source and interrogating each of the at least two optical fibers by using the optical switch to switch transmission amongst the at least two output channels, wherein the second pair of light pulses immediately follows the first pair of light pulses, and wherein the fourth pair of light pulses immediately follows the third pair of light pulses; and
(e) a phase modulator configured to apply, for each of the first, second, third, and fourth pairs of light pulses, a phase shift to at least one of the light pulses in the pair relative to the other of the light pulses in the pair, wherein one or more of:
(i) the phase shift applied to the at least one of the light pulses in the first pair of light pulses and the phase shift applied to the at least one of the light pulses in the second pair of light pulses are the same; and
(ii) the phase shift applied to the at least one of the light pulses in the third pair of light pulses and the phase shift applied to the at least one of the light pulses in the fourth pair of light pulses are the same.

18. The interrogator of claim 17 wherein the light source is operable to emit multiple wavelengths of light for interrogating different groups of the FBGs using wavelength division multiplexing.

19. A method for interrogating at least two optical fibers comprising fiber Bragg gratings (“FBGs”), the method comprising:
(a) generating first, second, third, and fourth pairs of light pulses from phase coherent light emitted from a light source, wherein the first, second, third, and fourth pairs of light pulses are generated by modulating the intensity of the light without splitting the light, wherein the second pair of light pulses immediately follows the first pair of light pulses, and wherein the fourth pair of light pulses immediately follows the third pair of light pulses;
(b) for each of the first, second, third, and fourth pairs of light pulses, applying a phase shift to at least one of the light pulses in the pair relative to the other of the light pulses in the pair, wherein one or more of:
(i) the phase shift applied to the at least one of the light pulses in the first pair of light pulses and the phase shift applied to the at least one of the light pulses in the second pair of light pulses are the same; and
(ii) the phase shift applied to the at least one of the light pulses in the third pair of light pulses and the phase shift applied to the at least one of the light pulses in the fourth pair of light pulses are the same;

(c) transmitting the first and second pairs

Assignees

• Hifi Eng Inc

Inventors

• Moore Brian H
• Shakespeare Walter Jeffrey
• Wallace Phillip William
• Hoang Viet
• Clement Tom

Classifications

• G01B11/161

  by interferometric means · CPC title

• G01B11/18

  using photoelastic elements · CPC title

• G01D18/00

  Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00 · CPC title

• G01D5/35316 Primary

  using a Bragg gratings · CPC title

• G01B2290/70

  Using polarization in the interferometer · CPC title