Two-core optical fibers for distributed fiber sensors and systems

• US 9,574,911 B2
• Filed: 10/24/2012
• Issued: 02/21/2017
• Est. Priority Date: 08/09/2012
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Hoover, Brett Jason, Li, Ming-Jun, Li, Shenping
• Primary Examiner(s): Ullah, Akm Enayet
• Assistant Examiner(s): MOONEY, MICHAEL P
• Application Number:
  US13/658,991
• Publication Number:
  US 20140042306A1
• Time in Patent Office: 1,581 Days
• Field of Search: 385/12, 385/13, 385/14, 385/39, 385123-127, 385/141, 356/32, 356/34, 356/35.5, 356/320, 250/227.14, 250/227.18
• US Class Current: 1/1
• CPC Class Codes: G01D 5/268 using optical fibres G01D5/28 - G01D5/38 take precedence
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01D 5/35364 using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01J 5/0821 Optical fibres
• CPC Class Codes: G01K 11/32 using changes in transmittance, scattering or luminescence in optical fibres
• CPC Class Codes: G01K 11/3206 at discrete locations in the fibre, e.g. using Bragg scattering
• CPC Class Codes: G01K 11/322 using Brillouin scattering
• CPC Class Codes: G01L 1/242 the material being an optical fibre
• CPC Class Codes: G01N 2021/638 Brillouin effect, e.g. stimulated Brillouin effect
• CPC Class Codes: G01N 21/636 using an arrangement of pump beam and probe beam; using the measurement of optical non-linear properties; non-linear optics per se G02F1/35
• CPC Class Codes: G01N 2201/088 Using a sensor fibre
• CPC Class Codes: G02B 6/02042 Multicore optical fibres
• CPC Class Codes: G02B 6/0281 Graded index region forming part of the central core segment, e.g. alpha profile, triangular, trapezoidal core G02B6/0288, G02B6/0286 take precedence
• CPC Class Codes: G02B 6/0365 arranged - - +

Abstract

A two-core optical fiber is provided for use in Brillouin distributed fiber sensor applications and systems. The two-core fiber includes a first and second core. Each core is configured to exhibit a Brillouin frequency shift greater than 30 Mhz relative to the other core. Further, each core possesses temperature and strain coefficients that differ from the other core. The cores can be configured to produce Brillouin frequency shift levels of at least 30 Mhz relative to one another. These differences in shift levels may be effected by adjustment of the material compositions, doping concentrations and/or refractive index profiles of each of the cores. These optical fibers may also be used in BOTDR- and BOTDA-based sensor systems and arrangements.

Claims

1. An optical fiber comprising:

a first core, a second core, and a cladding surrounding both of the cores, wherein at least one of the following conditions is satisfied;

(i) each core is configured with a refractive index profile that is substantially uniform along its length and differs from the refractive index profile of the other core;

(ii) each core is configured with a doping concentration that differs from the doping concentration of the other core;

(iii) each core has a different composition than the other core;

(iv) the optical fiber further comprises a refractive index ring configured to surround at least one of the cores;

(v) the cores are configured such that the distance between the center of the cores is at least 25 μ

m; and

(vi) the cores are configured such that the distance between the center of the cores is at least 25 μ

m and each core is surrounded by a low refractive index ring;

wherein each core is configured to exhibit a single Brillouin frequency shift peak (BFS peak) when light is launched into the core, and further wherein the BFS peak of each core differs from the BFS peak of the other core in terms of frequency and each core is configured to exhibit a Brillouin frequency shift of at least 30 Mhz relative to the other core.

2. The fiber according to claim 1, wherein each core is configured to exhibit a Brillouin frequency shift of at least 80 Mhz relative to the other core.

3. The fiber according to claim 1, wherein the optical fiber further comprises a refractive index ring configured to surround at least one of the cores.

4. The fiber according to claim 1, wherein the cores are configured such that the relative refractive index of the cores to the cladding is between about 0.2% to 2%.

5. The fiber according to claim 1, wherein the refractive index profile for each core is selected from the group consisting of step-shaped and graded index profiles.

6. The fiber according to claim 1, wherein each core is doped with germania.

7. The fiber according to claim 6, wherein each core is doped with approximately 1 to 10 mol % germania.

8. The fiber according to claim 3, wherein a trench separates the refractive index ring from the at least one of the cores.

9. The fiber according to claim 1, wherein the cores are further configured such that the distance between the center of the cores is at least 25 μ

m.

10. The fiber according to claim 6, wherein each core is doped with a different concentration of germania such that the absolute difference in dopant concentration between the cores is about 0.5 mol % or greater.

11. The fiber according to claim 10, wherein each core is doped with a different concentration of germania such that the absolute difference in dopant concentration between the cores is about 1.2 mol % or greater.

12. The fiber according to claim 10, wherein each core is doped with a different concentration of germania such that the absolute difference in dopant concentration between the cores is about 1.6 mol % or greater, and further wherein the cores are configured such that the distance between the center of the cores is about 55 μ

m and the cladding has an outer diameter of about 125 μ

m.

17. The fiber according to claim 1, wherein the distance between the center of the cores is at least 40 μ

m.

13. An optical fiber comprising:

a first core, a second core, and a cladding surrounding both of the cores, wherein at least one of the following conditions is satisfied;

(i) each core is configured with a refractive index profile that is substantially uniform along its length and differs from the refractive index profile of the other core;

(ii) each core is configured with a doping concentration that differs from the doping concentration of the other core;

(iii) each core has a different composition than the other core;

(iv) the optical fiber further comprises a refractive index ring configured to surround at least one of the cores;

(v) the cores are configured such that the distance between the center of the cores is at least 25 μ

m; and

(vi) the cores are configured such that the distance between the center of the cores is at least 25 μ

m and each core is surrounded by a low refractive index ring;

wherein each core is doped with a different concentration of germania such that the absolute difference in dopant concentration between the cores is about 0.5 mol % or greater.

14. An optical fiber comprising:

a first core, a second core, and a cladding surrounding both of the cores, wherein at least one of the following conditions is satisfied;

(i) each core is configured with a refractive index profile that is substantially uniform along its length and differs from the refractive index profile of the other core;

(ii) each core is configured with a doping concentration that differs from the doping concentration of the other core;

(iii) each core has a different composition than the other core;

(iv) the optical fiber further comprises a refractive index ring configured to surround at least one of the cores;

(v) the cores are configured such that the distance between the center of the cores is at least 25 μ

m; and

(vi) the cores are configured such that the distance between the center of the cores is at least 25 μ

m and each core is surrounded by a low refractive index ring;

wherein each core is doped with a different concentration of germania such that the absolute difference in dopant concentration between the cores is about 1.2 mol % or greater.

15. An optical fiber comprising:

a first core, a second core, and a cladding surrounding both of the cores, wherein at least one of the following conditions is satisfied;

(i) each core is configured with a refractive index profile that is substantially uniform along its length and differs from the refractive index profile of the other core;

(ii) each core is configured with a doping concentration that differs from the doping concentration of the other core;

(iii) each core has a different composition than the other core;

(iv) the optical fiber further comprises a refractive index ring configured to surround at least one of the cores;

(v) the cores are configured such that the distance between the center of the cores is at least 25 μ

m; and

(vi) the cores are configured such that the distance between the center of the cores is at least 25 μ

m and each core is surrounded by a low refractive index ring;

wherein each core is doped with a different concentration of germania such that the absolute difference in dopant concentration between the cores is about 1.6 mol % or greater, and further wherein the cores are configured such that the distance between the center of the cores is about 55 μ

m and the cladding has an outer diameter of about 125 μ

m.

16. An optical fiber comprising:

a first core, a second core, and a cladding surrounding both of the cores, wherein at least one of the following conditions is satisfied;

(i) each core is configured with a refractive index profile that is substantially uniform along its length and differs from the refractive index profile of the other core;

(ii) each core is configured with a doping concentration that differs from the doping concentration of the other core;

(iii) each core has a different composition than the other core;

(iv) the optical fiber further comprises a refractive index ring configured to surround at least one of the cores;

(v) the cores are configured such that the distance between the center of the cores is at least 25 μ

m; and

(vi) the cores are configured such that the distance between the center of the cores is at least 25 μ

m and each core is surrounded by a low refractive index ring;

wherein the fiber is further configured such that crosstalk between the cores is −

20 dB/km or less.

18. The fiber according to claim 16, wherein each core is configured to exhibit a single Brillouin frequency shift peak (BFS peak) when light is launched into the core, and further wherein the BFS peak of each core differs from the BFS peak of the other core in terms of frequency.

19. An optical fiber comprising:

a first core, a second core, and a cladding surrounding both of the cores, wherein at least one of the following conditions is satisfied;

(i) each core is configured with a refractive index profile that is substantially uniform along its length and differs from the refractive index profile of the other core;

(ii) each core is configured with a doping concentration that differs from the doping concentration of the other core;

(iii) each core has a different composition than the other core;

(iv) the optical fiber further comprises a refractive index ring configured to surround at least one of the cores;

(v) the cores are configured such that the distance between the center of the cores is at least 25 μ

m; and

the cores are configured such that the distance between the center of the cores is at least 25 μ

m and each core is surrounded by a low refractive index ring, wherein each core is configured to exhibit a single Brillouin frequency shift peak (BFS peak) when light is launched into the core, and further wherein the BFS peak of each core differs from the BFS peak of the other core in terms of frequency;

wherein each core is configured to exhibit a Brillouin frequency shift of at least 30 Mhz relative to the other core.

20. The optical fiber according to claim 19, wherein the cores are single mode cores at a 1550 nm wavelength.