AN OVERLAPPED CHIRPED FIBER BRAGG GRATING SENSING FIBER AND METHODS AND APPARATUS FOR PARAMETER MEASUREMENT USING SAME

• US 20160123715A1
• Filed: 06/10/2014
• Published: 05/05/2016
• Est. Priority Date: 06/13/2013
• Status: Active Grant

• Current Assignee: Intuitive Surgical Operations, Inc. (Intuitive Surgical Holdings, LLC)
• Original Assignee: Intuitive Surgical Operations, Inc. (Intuitive Surgical Holdings, LLC)
• Inventors: FROGGATT, Mark E., KLEIN, Justin W.
• Granted Patent: US 9,772,176 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01B 11/161 by interferometric means
• CPC Class Codes: G01B 11/18 using photoelastic elements
• CPC Class Codes: G01B 9/02002 using two or more frequencies
• CPC Class Codes: G01B 9/02004 using frequency scans
• CPC Class Codes: G01B 9/02044 Imaging in the frequency domain, e.g. by using a spectrometer
• CPC Class Codes: G01D 5/35316 using a Bragg gratings
• CPC Class Codes: G01M 11/3172 Reflectometers detecting the back-scattered light in the frequency-domain, e.g. OFDR, FMCW, heterodyne detection
• CPC Class Codes: G02B 2006/02157 Grating written during drawing of the fibre
• CPC Class Codes: G02B 6/02042 Multicore optical fibres
• CPC Class Codes: G02B 6/02085 characterised by the grating profile, e.g. chirped, apodised, tilted, helical
• CPC Class Codes: G02B 6/02114 characterised by enhanced photosensitivity characteristics of the fibre, e.g. hydrogen loading, heat treatment treatment of glass fibres by ion diffusion, implantation, radiation, C03C25/60, C03C25/62
• CPC Class Codes: G02B 6/02123 characterised by the method of manufacture of the grating photolithography G03F7/0005

Abstract

An optical sensor includes an optical fiber inscribed with a repeated refraction pattern such that light scattered from a location on the optical fiber is scattered at multiple frequencies in a range of frequencies. The inscribed patterns overlap at every measurement point along at least a portion of the length of the sensor. An optical sensing system including control circuitry coupled to the optical fiber detects measurement scatter data from the optical fiber over the range of frequencies, determines a change in the detected measurement scatter data over the range of frequencies, and extracts a parameter describing a state of the optical fiber from the determined change in the detected measurement scatter data. The sensor may be made by inscribing a first light refracting pattern on the optical fiber at every measurement point along at least a portion of the length of the sensor and inscribing a second light refracting pattern on the optical fiber that overlaps the first inscribed light refracting pattern at every measurement point along at least that portion of the length of the sensor.

Claims

1. An optical sensor comprising:

an optical fiber inscribed with a repeated refraction pattern at multiple locations along the optical fiber such that light reflected from a location on the optical fiber is reflected at multiple frequencies in a range of frequencies,

wherein at least two of the inscribed repeated refraction patterns overlap at every measurement point along at least a portion of the length of the sensor.

2. The optical sensor in claim 1, wherein the pattern includes overlapping chirped frequency fiber Bragg gratings.

3. The optical sensor in claim 1, wherein at least two of the refraction patterns overlap at every point along the entire length of the sensor.

4. The optical sensor in claim 1, further comprising multiple optical light guiding cores within the optical fiber, each of the multiple optical light guiding cores being inscribed with the repeated refraction patterns.

5. An optical sensing system comprising:

the optical sensor in claim 1,

control circuitry, coupled to the optical fiber, configured to;

detect measurement reflection data from the optical fiber over the range of frequencies,

determine a change in the detected measurement reflection data over the range of frequencies, and

determine a parameter describing a state of the optical fiber based on the determined change in the detected measurement reflection data.

6. The optical sensing system in claim 5, wherein the parameter is a measure of strain along a length of the optical sensor.

7. The optical sensing system in claim 1, wherein the parameter is a measure of change in optical phase along a length of the optical sensor.

8. The optical sensing system in claim 1, wherein the parameter is a measure of delay along a length of the optical sensor.

9. The optical sensing system in claim 8, wherein the control circuitry is configured to:

obtain baseline reflection data for the optical sensor;

Fourier transform the baseline reflection data from a temporal domain into a spectral domain;

generate a first half spectral response of the baseline reflection data and a second half spectral response of the baseline reflection data;

Fourier transform the detected measurement reflection data from the temporal domain into the spectral domain;

generate a first half spectral response of the detected measurement reflection data and a second half spectral response of the detected measurement reflection data;

process the first half spectral response of the baseline reflection data and the first half spectral response of the detected measurement reflection data to determine a first result;

process the second half spectral response of the baseline reflection data and the second half spectral response of the detected measurement reflection data to determine a second result; and

determine a measure of the delay based on the first and second results.

10. The optical sensing system in claim 9, wherein the control circuitry is configured to determine a phase difference from the processed spectral responses.

11. The optical sensing system in claim 5, wherein the control circuitry is configured to:

obtain baseline reflection data for the optical sensor, and

determine the delay based on a comparison that uses the baseline reflection data and the detected measurement reflection data.

12. The optical sensing system in claim 5, wherein the control circuitry is configured to use the delay to compensate for a misalignment between the baseline reflection data and the detected measurement reflection data.

13. The optical sensing system in claim 5, wherein the detected measurement reflection data has a scattering amplitude greater than 10 dB.

14. The optical sensing system in claim 5, wherein the pattern includes overlapping chirped frequency fiber Bragg gratings, and wherein the control circuitry is configured to determine a measure of a phase slope associated with a chirp rate of a grating, compare the measured phase slope to a phase slope generated from a baseline reflection measurement of the optical fiber, and determine a measure of strain at a location on the optical fiber based on the phase slope comparison.

15. The optical sensing system in claim 5, wherein the pattern includes overlapping chirped frequency fiber Bragg gratings, and wherein the control circuitry is configured to determine a measure of a phase slope associated with a chirp rate of a grating, compare the measured phase slope to a phase slope generated from a baseline reflection measurement of the optical fiber to determine a phase offset, and determine a measure of delay at a location on the optical fiber based on the phase offset.

16. The optical sensing system in claim 5, wherein the control circuitry is configured to use the detected measurement scatter data to determine a measure of delay along the length of the sensing fiber and use the measured delay to determine a measure of strain along the length of the optical fiber.

17. The optical sensing system in claim 5, wherein the pattern includes overlapping chirped frequency fiber Bragg gratings, and wherein the control circuitry is configured to extract a measure of delay along a length of the optical sensor by analyzing amplitude fluctuations in the gratings inscribed along the length of the sensor due to interference of the written gratings.

18. The optical sensing system in claim 5, wherein the pattern includes overlapping chirped frequency fiber Bragg gratings, and wherein the control circuitry is configured to filter out one or more of the chirped frequency fiber Bragg grating scattering responses from the overlapped chirped frequency fiber Bragg grating responses at a location along the optical sensor.

19. The optical sensing system in claim 5, wherein:

the control circuitry includes OFDR circuitry,

the pattern includes overlapping chirped frequency fiber Bragg gratings, and

a reflection wavelength of the overlapping chirped frequency fiber Bragg gratings exceeds a wavelength range of the OFDR circuitry and allows spectral shifts greater than a scan range of the OFDR circuitry to be measured by the OFDR circuitry.

20. A method for making an optical sensor that includes an optical fiber, the method comprising:

inscribing a first light refracting pattern on the optical fiber at every measurement point along at least a portion of the length of the sensor; and

inscribing a second light refracting pattern on the optical fiber that overlaps the first inscribed light refracting pattern at every measurement point along at least the portion of the length of the sensor, the second light refracting pattern having a same pattern as the first light refracting pattern,

wherein the optical fiber inscribed with the overlapping first and second light refracting patterns reflects light from a location on the optical fiber at multiple frequencies in a range of frequencies.

21. The method in claim 20, wherein the first and second light refracting patterns are overlapping chirped frequency fiber Bragg gratings.

22. The method in claim 20, wherein the first and second light refracting patterns overlap at every point along the entire length of the sensor.

23. The method in claim 20, wherein the first and second light refracting patterns create an overlapped modulated index of refraction pattern.