Shape sensing with multi-core fiber sensor

Patent metadata

Field	Value
Publication number	US-10823627-B2
Application number	US-201716342524-A
Country	US
Kind code	B2
Filing date	Oct 20, 2017
Priority date	Oct 21, 2016
Publication date	Nov 3, 2020
Grant date	Nov 3, 2020

Abstract

Shape sensing with a multi-core fiber can achieve high accuracy as well as accommodate small bend radii by measuring signals with peripheral waveguide cores placed at multiple different radial distances from the center axis of the fiber, and computing strain metrics from signals of cores selected based on the respective radial distances and a determination of whether the waveguide cores have strained out of range.

First claim

What is claimed is:

1. A shape-sensing system comprising:
a multi-core optical fiber having embedded therein:
a central waveguide core placed along a center axis of the optical fiber; and
at least four helically wound peripheral waveguide cores placed at fixed radial distances from the center axis, a value of a first radial distance of the fixed radial distances differing from a value of at least a second radial distance of the fixed radial distances; and

a plurality of interrogators coupled to the central and peripheral waveguide cores;
at an output of the plurality of interrogators, acquisition electronics configured to measure signals resulting at least in part from light reflected in the central and peripheral waveguide cores; and
a processing facility configured to compute, for each of a plurality of positions along the fiber, one or more strain metrics from the signals associated with the central waveguide core and at least three peripheral waveguide cores selected among the at least four peripheral waveguide cores based on the fixed radial distances of the waveguide cores from the center axis in conjunction with a determination of whether the waveguide cores have strained out of range.

2. The system of claim 1 , wherein the processing facility is configured to select the at least three peripheral waveguide cores by ranking those peripheral waveguide cores among the at least four peripheral waveguide cores that are determined to be within range based on their respective radial distances in an order from longest radial distance to shortest radial distance, and selecting at least three of the highest-ranking waveguide cores.

3. The system of claim 1 , wherein the peripheral waveguide cores comprise a plurality of inner waveguide cores placed at the first radial distance and a plurality of outer waveguide cores placed at the second radial distance, the second radial distance being greater than the first radial distance.

4. The system of claim 3 , wherein the second radial distance is greater than then the first radial distance by a factor of at least 1.7.

5. The system of claim 3 , wherein the second radial distance is about twice the first radial distance.

6. The system of claim 3 , wherein the plurality of inner waveguide cores comprises three inner waveguide cores positioned at vertices of a first equilateral triangle, and wherein the plurality of outer waveguide cores comprises three outer waveguide cores positioned at vertices of a second equilateral triangle.

7. The system of claim 6 , wherein the processing facility is configured to select, for computing the one or more strain metrics, the three outer waveguide cores if the signals associated with the three outer waveguide cores are all within range, and otherwise the three inner waveguide cores.

8. The system of claim 3 , wherein the peripheral waveguide cores consist of no more than six cores.

9. The system of claim 3 , wherein the determination of whether the outer waveguide cores have strained out of range is based on a comparison of respective predicted strains computed from the signals associated with the inner waveguide cores against a specified strain threshold.

10. The system of claim 1 , wherein the optical fiber is manufactured from a preform comprising a hexagonal arrangement of nineteen silica rods all sharing a common diameter, a central one of the rods and between four and six other ones of the nineteen silica rods being doped to form the central and peripheral waveguide cores.

11. The system of claim 1 , wherein the central and peripheral waveguide cores include fiber Bragg gratings, and wherein the determination of whether the peripheral waveguide cores have strained out of range is based on a comparison of strain-induced wavelength shifts of respective fiber Bragg gratings against a tuning range of a laser coupling light into the plurality of interrogators.

12. A method comprising:
measuring optical signals resulting from interrogation of a multi-core optical fiber including a central waveguide core and at least four helically wound peripheral waveguide cores, the peripheral waveguide cores being placed at respective fixed radial distances from a center axis, a value of a first radial distance of the fixed radial distances differing from a value of at least a second radial distance of the fixed radial distances; and
using a processing facility to determine, for each of a plurality of positions along the fiber, which of the at least four peripheral waveguide cores are useful for strain measurements, and to select, among the peripheral waveguide cores determined to be useful for strain measurements, at least three peripheral waveguide cores based on the respective fixed radial distances of the peripheral waveguide cores from the center axis, giving preference to peripheral waveguide cores with greater fixed radial distances; and
using the processing facility to compute a strain profile for the optical fiber from strain metrics evaluated, for each of the positions along the fiber, based on the optical signals associated with the central waveguide core and the selected peripheral waveguide cores.

13. The method of claim 12 , wherein the at least three peripheral waveguide cores are selected by ranking the peripheral waveguide cores determined to be useful for strain measurements based on their respective radial distances in an order from longest radial distance to shortest radial distance, and selecting at least three of the highest-ranking waveguide cores.

14. The method of claim 12 , wherein the peripheral waveguide cores comprise three inner waveguide cores placed at the first radial distance and three outer waveguide cores placed at the second radial distance, the second radial distance being greater than the first radial distance, and wherein the strain profile is computed from strain metrics evaluated based on the optical signals for the three outer waveguide cores at all positions along the fiber at which all three outer waveguide cores are useful for strain measurements and from strain metrics evaluated based on the optical signals for the three inner waveguide cores at all other positions along the fiber.

15. The method of claim 12 , wherein the peripheral waveguide cores comprise inner waveguide cores placed at the first radial distance and outer waveguide cores placed at the second radial distance, the second radial distance being greater than the first radial distance, and wherein the outer waveguide cores are determined to be useful for strain measurements if predicted strains computed from the signals associated with the inner waveguide cores are below a specified strain threshold.

16. The method of claim 12 , wherein the central and peripheral waveguide cores include fiber Bragg gratings, and wherein a waveguide core is determined to be useful for strain measurements at a given position along the optical fiber if a wavelength shift of a fiber Bragg grating at that position is below a specified wavelength shift threshold.

17. A non-transitory computer-readable medium storing instructions for controlling the operation of one or more hardware processors to compute a strain profile of a multi-core optical fiber from optical signals measured for a central waveguide core and at least four helically wound peripheral waveguide cores of the optical fiber, the peripheral waveguide cores being placed at fixed radial distances from the center axis, the instructions, when executed, causing the one or more hardware processors to:
determine, for each of a plurality of positions along the fiber, which of the peri

Assignees

• Intuitive Surgical Operations

Inventors

• Sanborn Eric E
• Froggatt Mark E
• Gifford Dawn K
• Lacroix Jeffrey T
• Roye Patrick
• Sang Alexander K

Classifications

• G01B11/18

  using photoelastic elements · CPC title

• G01M11/088

  of optical fibres; Mechanical features associated with the optical testing of optical fibres · CPC title

• G02B6/022

  using mechanical stress, e.g. tuning by compression or elongation, special geometrical shapes such as "dog-bone" or taper (G02B6/02204 takes precedence; optical modulation using photo-elastic effect G02F1/0131) · CPC title

• G01B11/165

  by means of a grating deformed by the object · CPC title

• G01L1/242

  the material being an optical fibre · CPC title