Glass large-core optical fibers

• US 10,353,144 B2
• Filed: 03/24/2017
• Issued: 07/16/2019
• Est. Priority Date: 09/26/2007
• Status: Active Grant

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Dong, Liang, Li, Jun, McKay, Hugh, Fu, Libin, Marcinkevicius, Andrius
• Primary Examiner(s): Bolda, Eric L
• Application Number:
  US15/468,520
• Publication Number:
  US 20170322370A1
• Time in Patent Office: 844 Days
• CPC Class Codes: G02B 6/02009 Large effective area or mode field radius, e.g. to reduce nonlinear effects in single mode fibres
• CPC Class Codes: G02B 6/02333 Core having higher refractive index than cladding, e.g. solid core, effective index guiding
• CPC Class Codes: G02B 6/02357 Property of longitudinal structures or background material varies radially and/or azimuthally in the cladding, e.g. size, spacing, periodicity, shape, refractive index, graded index, quasiperiodic, quasicrystals
• CPC Class Codes: G02B 6/02361 Longitudinal structures forming multiple layers around the core, e.g. arranged in multiple rings with each ring having longitudinal elements at substantially the same radial distance from the core, having rotational symmetry about the fibre axis
• CPC Class Codes: G02B 6/02366 Single ring of structures, e.g. "air clad"
• CPC Class Codes: G02B 6/02371 Cross section of longitudinal structures is non-circular
• CPC Class Codes: G02B 6/0283 Graded index region external to the central core segment, e.g. sloping layer or triangular or trapezoidal layer G02B6/0288, G02B6/0286 take precedence
• CPC Class Codes: G02B 6/0288 Multimode fibre, e.g. graded index core for compensating modal dispersion
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: H01S 3/06729 Peculiar transverse fibre profile
• CPC Class Codes: H01S 3/06754 Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/091 using optical pumping

Abstract

Embodiments of optical fiber may include cladding features that include a material (e.g., fluorine-doped silica glass) that may produce a very low relative refractive index difference with respect to cladding material in which the cladding features are disposed. This relative refractive index difference may be characterized by (n₁−n₂)/n₁, where n₁ is the index of refraction of the cladding material in which the cladding features are included, and n₂ is the index of refraction of the cladding features. In certain embodiments, the relative refractive index difference may be less than about 4.5×10⁻³. In various embodiments, the configuration of the cladding features including, for example, the size and spacing of the cladding features, can be selected to provide for confinement of the fundamental mode yet leakage for the second mode and higher modes, which may provide mode filtering, single mode propagation, and/or low bend loss.

Claims

1. A fiber having a fiber diameter, the fiber comprising:

an inner cladding region comprising a first cladding material having a first index of refraction, n1;

inner cladding features disposed in said inner cladding region, said cladding features comprising a second cladding material having a second index of refraction, n2, where n2 is less than n1;

a core region at least partially surrounded by said inner cladding features; and

one or more outer cladding regions at least partially surrounding said inner cladding features,

wherein said fiber diameter, said inner cladding region, and said inner cladding features are configured to propagate a fundamental mode substantially within a region bounded by said core region, said fundamental mode having a wavelength, and

wherein said fiber diameter increases confinement loss of a second order mode at said wavelength to be significantly higher than the confinement loss of the fundamental mode at said wavelength.

2. The fiber of claim 1, wherein the fiber diameter increases confinement loss of the second order mode at said wavelength at least by about 3 dB/m relative to the confinement loss of a second order mode at a different fiber diameter at said wavelength;

and this confinement loss is at least about 3 dB/m greater than the confinement loss of the fundamental mode.

3. The fiber of claim 1, wherein the fiber diameter is referenced to an outer edge of the inner cladding region.

4. The fiber of claim 1, wherein the fiber diameter is referenced to a reflective boundary of an outer cladding region.

5. The fiber of claim 1, wherein an outer cladding region comprises a coating.

6. The fiber of claim 1, wherein at least one of the one or more outer cladding regions comprises a pump cladding.

7. The fiber of claim 1, wherein at least one of the one or more outer cladding regions comprises air holes.

8. The fiber of claim 1, wherein each of the one or more outer cladding regions comprises a reflective outer boundary.

9. The fiber of claim 1, wherein the second order mode is near an anti-crossing.

10. The fiber of claim 1, wherein the second order mode has a modal index that would be the same as a modal index of a higher order cladding mode if the two modes did not cross.

11. The fiber of claim 1, wherein a modal index for the second order mode has a discontinuity near the fiber diameter.

12. The fiber of claim 1, wherein the second order mode confinement loss is at least about 3 dB/m greater than the fundamental mode confinement loss.

13. The fiber of claim 1, wherein the second order mode confinement loss is at least about 5 dB/m greater than the fundamental mode confinement loss.

14. The fiber of claim 1, wherein the second order mode confinement loss is at least 10 times greater than the fundamental mode confinement loss.

15. The fiber of claim 1, wherein the fiber diameter and one or a combination of dimensions of the inner cladding features provides higher order mode confinement loss greater than the fundamental mode confinement loss.

16. The fiber of claim 15, wherein the fiber is configured as a double clad fiber.

17. The fiber of claim 1, wherein at least one of the one or more outer cladding regions comprises a coating having a refractive index, wherein said refractive index of said coating and said fiber diameter increases confinement loss of the second order mode at said wavelength to be significantly higher than the confinement loss of the fundamental mode at said wavelength.

18. The fiber of claim 1, wherein at least one of the inner cladding features comprises a glass-filled hole.

19. The fiber of claim 1, wherein at least one of the inner cladding features comprises fluorine-doped silica glass or boron-doped silica glass.

20. The fiber of claim 1, wherein the fiber is all-glass.

21. The fiber of claim 1, wherein a relative refractive index Δ

_c=(n1−

n2)/n1 is less than 8.3×

10<sup>−

4</sup>.

22. The fiber of claim 1, wherein a relative refractive index Δ

_c=(n1−

n2)/n1 is in a range from about 2×

10<sup>−

4</sup> to 4.5×

10<sup>−

3</sup>.

23. The fiber of claim 1, wherein the inner cladding features are arranged in N≥

1 layers.

24. The fiber of claim 23, wherein 1≤

N≤

3.

25. The fiber of claim 23, wherein N=2.

26. The fiber of claim 1, wherein a diameter of said core region is in a range from 30 μ

m to 200 μ

m.

27. The fiber of claim 1, wherein the fiber diameter is in a range from 125 μ

m to 700 μ

m.

28. The fiber of claim 1, wherein said inner cladding features have a dimension d and a center-to-center spacing Λ

, and a ratio of d/Λ

is in a range from 0.3 to 0.9.

29. The fiber of claim 28, wherein the inner cladding features comprise an inner layer and an outer layer, and the ratio of d/Λ

for the outer layer is smaller than the ratio of d/Λ

for the inner layer.

30. The fiber of claim 1, further comprising a layer of air holes surrounding the inner cladding region.

31. The fiber of claim 1, wherein the inner cladding region comprises stress elements.

32. The fiber of claim 1, configured to be polarization maintaining.

33. The fiber of claim 1, wherein at least a portion of the core region is rare-earth doped.

34. A fiber optic amplifier system comprising:

an optical pulse source configured to provide optical pulses;

an optical pump source; and

the optical fiber of claim 1, wherein at least a portion of the core region is doped to provide an optical gain medium, at least one of the one or more outer cladding regions comprises a pump cladding, the pump cladding configured to receive pump energy from said optical pump source,

said optical fiber configured to receive and amplify said optical pulses so as to produce output pulses having nearly diffraction limited output spatial profiles and at least one output pulse having energy in a range from about 10 μ

J to about 10 mJ.

35. The fiber optic amplifier system of claim 34, further comprising a single mode or few-mode input fiber configured to receive pulses from said optical pulse source and to provide input pulses to said optical fiber.

36. The fiber optic amplifier system of claim 35, said optical fiber and said input fiber joined such that a core of said input fiber is expanded, and power coupled from the core of said input fiber to said core region of said optical fiber is substantially greater than obtainable with butt-coupling.

37. The fiber optic amplifier system of claim 36, wherein a mode at an output of said input fiber is substantially matched to the fundamental mode of said optical fiber.

38. The fiber optic amplifier system of claim 34, wherein the optical fiber comprises at least a non-circular portion.