Methods and apparatus to determine a twist parameter and/or a bend angle associated with a multi-core fiber

Patent metadata

Field	Value
Publication number	US-11473902-B2
Application number	US-202117142634-A
Country	US
Kind code	B2
Filing date	Jan 6, 2021
Priority date	Sep 18, 2009
Publication date	Oct 18, 2022
Grant date	Oct 18, 2022

Abstract

A multi-core fiber includes multiple optical cores, and for each different core of a set of different cores of the multiple optical cores, a total change in optical length is detected. The total change in optical length represents an accumulation of all changes in optical length for multiple segments of that different core up to a point on the multi-core fiber. A difference is determined between the total changes in optical length for cores of the set of different cores. A twist parameter and/or a bend angle associated with the multi-core fiber at the point on the multi-core fiber is/are determined based on the difference.

First claim

What is claimed is:

1. A shape-sensing method for a multi-core optical fiber comprising multiple cores, each core of the multiple cores including a continuous fiber grating along a length of the optical fiber, the method comprising:
for each core of the multiple cores, measuring light reflected by the fiber grating in the core;
for each core of the multiple cores, processing the reflected light to track an associated total phase shift continuously along the length of the optical fiber, the total phase shift at each position along the optical fiber resulting from cumulative distortions up to that position in a period of the fiber grating of the core, the phase shift being relative to a phase in an undistorted reference state of the fiber grating;
determining, based on the continuously tracked total phase shifts associated with the multiple cores, a shape of the optical fiber.

2. The method of claim 1 , wherein determining the shape of the optical fiber comprises tracking a pointing vector along the optical fiber by:
computing two orthogonal differential strain signals from derivatives of the phase shifts tracked for two cores of the multiple cores;
using a discrete representation of the orthogonal differential strain signals to compute rotation matrices for segments along the optical fiber; and
computing local pointing vectors from the rotation matrices.

3. The method of claim 2 , wherein determining the shape of the optical fiber further comprises determining a position and direction at a point along the optical fiber by summing all local pointing vectors up to that point.

4. The method of claim 2 , wherein the orthogonal differential strain signals are based in part on wobble and twist signals measured along the optical fiber.

5. The method of claim 1 , wherein the light reflected by the fiber gratings is measured at two mutually orthogonal polarization states for each of two mutually orthogonal input polarizations of light coupled into the optical fiber, the method further comprising:
computing a birefringence correction based on the measured reflected light at the two mutually orthogonal polarization states for each of the two mutually orthogonal input polarizations, the birefringence correction being used in determining the shape of the optical fiber.

6. The method of claim 5 , wherein the multiple cores comprise a central core and a plurality of outer cores, and wherein determining the shape of the optical fiber comprises computing, for each core of the plurality of outer cores, a second-order birefringence correction based on phase responses of cores of the plurality of outer cores.

7. A shape-sensing system for a multi-core optical fiber comprising multiple cores, each core of the multiple cores including a continuous fiber grating along a length of the optical fiber, the system comprising:
a plurality of acquisition interferometers and associated data acquisition networks to measure light reflected by the fiber gratings in the multiple cores of the optical fiber; and
a system controller and data processor to process the measured reflected light signals to:
for each core of the multiple cores, track an associated total phase shift continuously along the length of the optical fiber, the total phase shift at each position along the optical fiber resulting from cumulative distortions up to that position in a period of the fiber grating of the associated core, the total phase shift being relative to a phase in an undistorted reference state of the fiber grating; and
determine a shape of the optical fiber based on the continuously tracked total phase shifts associated with the multiple cores.

8. The shape-sensing system of claim 7 , wherein the light reflected by the fiber gratings is measured and the reflected light is processed using optical frequency domain reflectometry (OFDR).

9. The shape-sensing system of claim 7 ,
wherein the system controller and data processor is configured to determine the shape of the optical fiber by tracking a pointing vector along the optical fiber; and wherein
tracking the pointing vector comprises: computing two orthogonal differential strain signals from derivatives of the phase shifts tracked for two cores of the multiple cores.

10. The shape-sensing system of claim 9 , wherein tracking the pointing vector further comprises:
using a discrete representation of the orthogonal differential strain signals to compute rotation matrices for segments along the optical fiber; and
computing local pointing vectors from the rotation matrices.

11. The shape-sensing system of claim 9 , wherein the system controller and data processor is configured to determine the shape of the optical fiber by determining positions and directions at points along the optical fiber by summing all local pointing vectors up to those points.

12. The shape-sensing system of claim 9 , wherein the orthogonal differential strain signals are based in part on wobble and twist signals measured along the optical fiber.

13. The shape-sensing system of claim 12 wherein the multiple cores comprise one or more helical cores, the wobble signal representing a departure of a spin rate of the one or more helical cores from a constant nominal spin rate.

14. The shape-sensing system of claim 7 , further comprising a tunable laser, wherein the system controller and data processor further initiate sweeps of the tunable laser over a defined wavelength range to interrogate the multiple cores.

15. The shape-sensing system of claim 14 , further comprising a polarization controller to rotate light received from a tunable laser between two successive laser scans to obtain a first input polarization during a first scan and a second input polarization during a second scan, the second input polarization being orthogonal to the first input polarization, wherein the light reflected by the fiber gratings is measured at two mutually orthogonal polarization states for each of the first and second input polarizations.

16. The shape-sensing system of claim 15 , wherein the system controller and data processor further computes a birefringence correction based on the measured reflected light at the two mutually orthogonal polarization states for each of the first and second input polarizations, and uses the birefringence correction in determining the shape of the optical fiber.

17. The shape-sensing system of claim 16 , wherein the multiple cores comprise a central core and a plurality of outer cores, and wherein determining the shape of the optical fiber comprises computing, for each core of the plurality of outer cores, a second-order birefringence correction based on phase responses of cores of the plurality of outer cores.

18. A non-transitory computer-readable storage medium storing program instructions for processing light reflected by fiber gratings in multiple cores of a multi-core optical fiber, wherein the program instructions, when executed by a computer, cause the computer to perform operations comprising:
tracking, for each core of the multiple cores, an associated total phase shift continuously along a length of the optical fiber, the total phase shift at each position along the optical fiber resulting from cumulative distortions up to that position in a period of the fiber grating of the associated core, the total phase shift being relative to a phase in an undistorted reference state of the fiber grating; and
based on the continuously tracked total phase shifts associated with the multiple cores, determining a shape of the optical fiber.

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Assignees

• Intuitive Surgical Operations

Inventors

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

Classifications

• G01B11/18

  using photoelastic elements · CPC title

• G01B11/16

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

• G01M11/331

  by using interferometer · CPC title

• G01M11/3172

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