Microstructured optical fiber sensor

Patent metadata

Field	Value
Publication number	US-12158377-B2
Application number	US-202017767244-A
Country	US
Kind code	B2
Filing date	Oct 8, 2020
Priority date	Oct 8, 2019
Publication date	Dec 3, 2024
Grant date	Dec 3, 2024

Abstract

A microstructured optical fiber sensor for sensing changes in a physical characteristic up to a predetermined temperature is disclosed. The sensor includes a microstructured optical fiber and a fiber Bragg grating formed in the microstructured optical fiber by generating a periodic modulation in the refractive index along a core region of the suspended core. The fiber Bragg grating is configured to produce a band reflection spectra including a fundamental mode and a plurality of higher order modes whose respective wavelengths vary in accordance with changes in the physical characteristic at the core region of the microstructured optical fiber. The microstructured optical fiber is configured to increase the confinement loss of the plurality of higher order modes of the band reflection spectra relative to the fundamental mode.

First claim

The invention claimed is:

1. A microstructured optical fiber sensor operable up to a predetermined temperature for sensing changes in a physical characteristic, comprising:
a microstructured optical fiber comprising:
an inner suspended core;
an outer jacket region;
at least three longitudinal channels extending along the microstructured optical fiber;
intra-channel struts separating the at least three longitudinal channels and extending radially from the inner suspended core to the outer jacket region;
a fiber Bragg grating formed in the microstructured optical fiber by generating a periodic modulation in the refractive index along a core region of the suspended core, the fiber Bragg grating configured to produce a band reflection spectra comprising a fundamental mode and a plurality of higher order modes whose respective wavelengths vary in accordance with changes in the physical characteristic at the core region of the microstructured optical fiber, wherein the microstructured optical fiber is configured in operation to increase a confinement loss of the plurality of higher order modes of the band reflection spectra relative to the fundamental mode,
wherein the microstructured optical fiber sensor includes an interrogation end for measurement of the band reflection spectra and an operating length corresponding to the distance between a sensing location comprising the fiber Bragg grating and the interrogation end,
wherein the microstructured optical fiber sensor is configured to have a predetermined confinement loss of the plurality of higher order modes relative to the fundamental mode based on the operating length, and
wherein the predetermined confinement loss of the plurality of higher order modes of the band reflection spectra relative to the fundamental mode is selected to suppress the plurality of higher order modes to allow measurement only of the fundamental mode at the interrogation end.

2. The microstructured optical fiber sensor of claim 1 , wherein the intra-channel struts have a corresponding strut width and the inner suspended core has a core diameter and wherein the microstructured optical fiber is configured to have the strut width between 0.25-0.5 times the core diameter.

3. The microstructured optical fiber sensor of claim 2 , wherein the microstructured optical fiber is configured to have the strut width between 0.27-0.48 times the core diameter.

4. The microstructured optical fiber sensor of claim 3 , wherein the microstructured optical fiber is configured to have the strut width between 0.29-0.45 times the core diameter.

5. The microstructured optical fiber sensor of claim 1 , wherein the intra-channel struts have a corresponding strut length and wherein the microstructured optical fiber is configured to have the strut length at least greater than or equal to the core diameter.

6. The microstructured optical fiber sensor of claim 5 , wherein the microstructured optical fiber is configured to have the strut length at least twice the core diameter.

7. The microstructured optical fiber sensor of claim 6 , wherein the microstructured optical fiber is configured to have the strut length at least three times the core diameter.

8. The microstructured optical fiber sensor of claim 1 , wherein the microstructured optical fiber sensor is further configured to have a fundamental node confinement loss of the fundamental mode over the operating length of less than a predetermined loss parameter and a suppression ratio comparing the loss of a first higher order mode to the fundamental mode over the operating length greater than a predetermined suppression ratio.

9. The microstructured optical fiber sensor of claim 8 , wherein the predetermined loss parameter of the fundamental mode is less than 60 dB.

10. The microstructured optical fiber sensor of claim 8 , wherein the predetermined suppression ratio is greater than 3.

11. The microstructured optical fiber sensor of claim 1 , wherein a size of the suspended core is configured to be matched with a single mode fiber (SMF) carrier.

12. The microstructured optical fiber sensor of claim 1 , wherein the physical characteristic is temperature.

13. The microstructured optical fiber sensor of claim 1 , wherein the physical characteristic is strain.

14. The microstructured optical fiber sensor of claim 1 , wherein the physical characteristic is pressure.

15. The microstructured optical fiber sensor of claim 1 , wherein the periodic modulation in the refractive index along the core region is formed by laser ablating defects along the core region of the microstructured optical fiber.

16. The microstructured optical fiber sensor of claim 15 , wherein the microstructured optical fiber is formed of silica material and the sensor is configured for a predetermined temperature of at least 700° C.

17. The microstructured optical fiber sensor of claim 15 , wherein the microstructured optical fiber is formed of silica material and the sensor is configured for a predetermined temperature of at least 1000° C.

18. The microstructured optical fiber sensor of claim 15 , wherein the microstructured optical fiber is formed of silica material and the sensor is configured for a predetermined temperature of at least 1350° C.

19. The microstructured optical fiber sensor of claim 15 , wherein the microstructured optical fiber is formed of silica material and the sensor is configured for a predetermined temperature of at least 1550° C.

20. The microstructured optical fiber sensor of claim 15 , wherein the microstructured optical fiber is formed of sapphire crystal and the sensor is configured for a predetermined temperature of at least 1600° C.

21. The microstructured optical fiber sensor of claim 15 , wherein the microstructured optical fiber is formed of sapphire crystal and the sensor is configured for a predetermined temperature of at least 2000° C.

22. The microstructured optical fiber sensor according to claim 1 , wherein the sensor includes a second fiber Bragg grating formed in the microstructured optical fiber by generating a periodic modulation in the refractive index along a second core region of the microstructured optical fiber, the second core region spaced from the core region of the fiber Bragg grating, wherein the second fiber Bragg grating is configured to produce a second band reflection spectra at different wavelengths to the band reflection spectra of the fiber Bragg grating, the second band reflection spectra comprising a second fundamental mode and a plurality of associated higher order modes, wherein the respective wavelengths of the second band reflection spectra vary in accordance with changes in the physical characteristic at the second core region of the microstructured optical fiber, wherein the microstructured optical fiber is configured in operation to increase a confinement loss of the plurality of associated higher order modes of the second band reflection spectra relative to the second fundamental mode.

23. A sensing system comprising:
a source of electromagnetic radiation;
a microstructured optical fiber sensor as claimed in claim 1 , the microstructured optical fiber sensor interfaced to the source of electromagnetic radiation;
a detector for detecting the band reflection spectra from the core region of the microstructured optical fiber sensor where the fiber Bragg grating is located, the detector interfaced to the microstructured optical fiber sensor; and
a data processor for determining a phy

Assignees

• Univ Adelaide

Inventors

• Warren-Smith Stephen Christopher
• Ebendorff-Heidepriem Heike
• Nguyen Viet Linh
• Schartner Erik Peter

Classifications

• G02B6/02366

  Single ring of structures, e.g. "air clad" · CPC title

• G02B6/02176 Primary

  due to temperature fluctuations · CPC title

• G01L1/246

  using integrated gratings, e.g. Bragg gratings · CPC title

• G02B6/02204

  using thermal effects, e.g. heating or cooling of a temperature sensitive mounting body (optical modulation using thermo-optic effect G02F1/0147) · 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