Methods and apparatus to determine strain on an optical core based on tracked change in phase

Patent metadata

Field	Value
Publication number	US-9784569-B2
Application number	US-201414326004-A
Country	US
Kind code	B2
Filing date	Jul 8, 2014
Priority date	Sep 18, 2009
Publication date	Oct 10, 2017
Grant date	Oct 10, 2017

Abstract

An accurate measurement method and apparatus using an optical fiber are disclosed. A total change in optical length in an optical core in the optical fiber is determined that reflects an accumulation of all of the changes in optical length for multiple segment lengths of the optical core up to a point on the optical fiber. The total change in optical length in the optical core is provided for calculation of an average strain over a length of the optical core based on the detected total change in optical length.

First claim

The invention claimed is:

1. A measurement method for an optical fiber having an optical core, comprising:
tracking a change in phase associated with a strain on the optical core over a length of the optical core, where the tracked change in phase is proportional to a total change in optical length in the optical core of the optical fiber, the total change indicative of an accumulation of all changes in optical length for multiple segment lengths of the optical core up to a point on the optical core, and
determining the strain over the length of the optical core based on the tracked change in phase.

2. The method in claim 1 , wherein the tracking step includes:
using optical frequency domain reflectometry (OFDR) to obtain phase data values along the optical core.

3. The method in claim 2 , wherein the optical core is divided into multiple segments, and wherein the determining step further comprises:
obtaining a reference measurement for each of the multiple segments for producing a reference data set for each of the multiple segments;
obtaining a subsequent test measurement for each of the multiple segments for producing a test data set for each of the multiple segments;
determining a delay to one segment in the multiple segments;
adjusting the delay to the one segment to align the reference and test data sets; and
calculating a phase change between the aligned reference and test data sets.

4. The method in claim 1 , wherein the tracking step includes detecting an incremental change in optical length in the optical core in the optical fiber for each of the multiple segment lengths up to the point on the optical fiber, and wherein the total change in optical length is based on a combination of the incremental changes.

5. The method in claim 4 , wherein the tracking step further includes detecting a phase response of a light signal reflected in the optical core of the optical fiber from the multiple segment lengths, and wherein strain on the optical fiber at the multiple segment lengths causes a phase shift in the reflected light signal from the multiple segment lengths in the optical core.

6. The method in claim 5 , further comprising monitoring the phase response continuously along the optical length in the optical core of the optical fiber.

7. The method in claim 5 , further comprising, for each segment length of the multiple segment lengths:
detecting a reflected Rayleigh scatter pattern in the reflected light signal for each segment length,
comparing the reflected Rayleigh scatter pattern with a reference Rayleigh scatter pattern for each segment length, and
determining the phase response for each segment length based on the comparing.

8. The method in claim 1 , further comprising:
calculating an optical phase change at each segment length of the multiple segment lengths along the optical fiber, and
unwrapping the optical phase change.

9. The method in claim 1 , further comprising:
transmitting light with at least two polarization states along the optical fiber, and
combining reflections of the light with the at least two polarization states in determining changes in optical length.

10. The method in claim 9 , wherein the two polarization states include a first polarization state and a second polarization state which are at least nominally orthogonal, and the method further comprises:
using a polarization controller to transmit a first light signal at the first polarization state along the optical fiber,
using the polarization controller to transmit a second light signal at the second polarization state along the optical fiber, and
calculating a polarization-independent change in optical length in the core of the optical fiber up to the point on the optical fiber using reflections of the first and second light signals.

11. An apparatus for making measurements of using an optical fiber having an optical core, comprising:
detection circuitry configured to track a change in phase associated with a strain on the optical core over a length of the optical core, where the tracked change in phase is proportional to a total change in optical length in the optical core in the optical fiber, the total change indicative of an accumulation of all of the changes in optical length for multiple segment lengths of the optical core up to a point on the optical fiber, and
processing circuitry configured to determine the strain over the length of the optical core based on the tracked change in phase.

12. The apparatus in claim 11 , wherein the detection circuitry is configured to use optical frequency domain reflectometry to obtain phase data values along the optical core.

13. The apparatus in claim 12 , wherein the optical core is divided into multiple segments, and wherein the detection circuitry is configured to:
obtain a reference measurement for each of the multiple segments for producing a reference data set for each of the multiple segments;
obtain a subsequent test measurement for each of the multiple segments for producing a test data set for each of the multiple segments;
determine a delay to one segment in the multiple segments;
adjust the delay to the one segment to align the reference and test data sets; and
calculate a phase change between the aligned reference and test data sets.

14. The apparatus in claim 11 , wherein the detection circuitry is configured to track an incremental change in optical length in the optical core in the optical fiber for each of multiple segment lengths up to the point on the optical fiber, and wherein the total change in optical length is based on a combination of the incremental changes.

15. The apparatus in claim 11 , wherein the detection circuitry is configured to detect a phase response of a light signal reflected in the optical core of the optical fiber from multiple segment lengths, and wherein strain on the optical fiber at the multiple segment lengths causes a phase shift in the reflected light signal from the multiple segment lengths in the optical core.

16. The apparatus in claim 15 , wherein the detection circuitry is configured to monitor the phase response continuously along the optical length in the optical core of the optical fiber.

17. The apparatus in claim 15 , the detection circuitry is configured to, for each segment length of the multiple segment lengths:
detect a reflected Rayleigh scatter pattern in the reflected light signal for each segment length,
compare the reflected Rayleigh scatter pattern with a reference Rayleigh scatter pattern for each segment length, and
determine the phase response for each segment length based on the comparison.

18. The apparatus in claim 11 , wherein the processing circuitry is configured to calculate an optical phase change at each segment length of the multiple segment lengths along the optical fiber and to unwrap the optical phase change.

19. The apparatus in claim 11 , further comprising:
a transmitter configured to transmit light with at least two polarization states along the optical fiber, and
a combiner configured to combine reflections of the light with the at least two polarization states in determining changes in optical length.

20. The apparatus in claim 19 , wherein the two polarization states include a first polarization state and a second polarization state which are at least nominally orthogonal, the apparatus comprising:
a polarization controller configured to transmit a first light signal at the first polarization state along the optical fiber and a second light signal at th

Assignees

• Intuitive Surgical Operations

Inventors

• Froggatt Mark E
• Klein Justin W
• Gifford Dawn K
• Kreger Stephen Tod

Classifications

• G01M11/331

  by using interferometer · CPC title

• G01L1/242

  the material being an optical fibre · CPC title

• G01M11/31

  with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers · CPC title

• G01B11/24 Primary

  for measuring contours or curvatures · CPC title

• G01B11/16

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