Glass large-core optical fibers

• US 8,995,051 B2
• Filed: 04/05/2012
• Issued: 03/31/2015
• Est. Priority Date: 09/26/2007
• Status: Expired due to Fees

• 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:
  US13/440,215
• Publication Number:
  US 20120188632A1
• Time in Patent Office: 1,090 Days
• Field of Search: 359/341.1, 385/123, 385/125
• US Class Current: 359/341.1
• 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 comprising:

a first cladding region comprising a first cladding material having a first index of refraction, n1, the first cladding material comprising a first glass that comprises fused silica;

cladding features disposed in said first cladding region, said cladding features comprising a second cladding material having a second index of refraction, n2, wherein n2 is less than n1, said second cladding material comprising a second glass that comprises fluorine-doped silica glass or boron-doped silica glass; and

a core region at least partially surrounded by said cladding features, said first cladding region and said cladding features configured such that said core region propagates at least one lower order mode having a wavelength, while limiting propagation of at least one higher order mode having the wavelength by providing said at least one higher order mode with a higher loss than the at least one lower order mode at the wavelength.

2. The fiber of claim 1, wherein said first cladding region has a diameter in a range from about 125 μ

m to about 300 μ

m.

3. The fiber of claim 1, wherein said core region has a dimension diameter in a range from about 30 μ

m to about 200 μ

m.

4. The fiber of claim 1, wherein a mode profile of a fiber output is approximately diffraction limited over a substantial portion of a half-power region of the mode profile.

5. The fiber of claim 1, wherein at least one of the cladding features is non-rotationally symmetric.

6. The fiber of claim 1, wherein a relative refractive index difference characterized by (n1−

n2)/n1 is less than about 4.5×

10<sup>−

3</sup>.

7. The fiber of claim 6, wherein the relative refractive index difference is less than about 1.0×

10<sup>−

3</sup>.

8. The fiber of claim 1, further comprising a pump cladding disposed beyond said first cladding region.

9. The fiber of claim 8, wherein said pump cladding comprises a low index glass.

10. The fiber of claim 9, wherein said low index glass comprises fluorine.

11. The fiber of claim 8, wherein said pump cladding comprises a layer of air holes.

12. The fiber of claim 1, wherein said fiber comprises a doped core region to provide optical gain, a pump cladding, and a pump guide, and wherein at least a portion of said pump cladding or said pump guide comprises a non-circular portion, said non-circular portion configured to increase mode mixing of a pump beam incident on said pump cladding.

13. The fiber of claim 1, wherein the cladding features have a dimension d and a spacing Λ

, and a ratio d/Λ

is in a range from about 0.3 to about 0.9.

14. The fiber of claim 13, wherein the ratio d/Λ

is in a range from about 0.4 to about 0.8.

15. The fiber of claim 13, wherein the ratio d/Λ

is selected at least in part to provide a relative refractive index difference in at least a portion of the core region that is less than about 5×

10<sup>−

4</sup> within at least the portion of the core region but sufficiently large to cause index guiding of a fundamental mode within at least the portion of the core region.

16. The fiber of claim 15, wherein the first cladding material has a first thermal expansion coefficient, the second cladding material has a second thermal expansion coefficient, and the first thermal expansion coefficient and the second thermal expansion coefficient are selected at least in part to provide the relative refractive index difference.

17. The fiber of claim 1, wherein said first cladding region further comprises stress elements having an index of refraction different from the first index of refraction and the second index of refraction.

18. The fiber of claim 17, wherein said fiber is configured as a polarization-maintaining fiber, and one or a combination of dimension, arrangement, and number of said cladding features and stress elements provides said higher order loss while maintaining said beam polarization.

19. The fiber of claim 1, in combination with an input fiber comprising a single mode or few-mode fiber, said fiber of claim 1 configured as a large-core leakage channel fiber wherein a diameter of said core region is in a range from about 30 μ

m to about 200 μ

m, said large-core leakage channel fiber having an input end configured to be coupled to an output end of the input fiber, the output end of the input fiber and the input end of the large-core leakage channel fiber configurable such that (i) a core of said input fiber at said output end is expanded and (ii) optical signal power coupled from the expanded core of the input fiber to the leakage channel fiber is substantially greater than obtainable with butt-coupling.

20. A fiber optic system comprising:

a source of optical pulses;

a single mode or few-mode input fiber configured to receive pulses from said source; and

the fiber of claim 1 optically coupled to said input fiber and configured to receive said pulses from said input fiber,

said fiber of claim 1 and said input fiber being joined such that a core of said input fiber is expanded and power coupled from said input fiber core to said core region is substantially greater than obtainable with butt-coupling, and a mode at an output of said input fiber is substantially matched to a fundamental mode of said fiber of claim 1.

21. A laser radar, a material processing system, or a telecommunications system comprising the fiber optic system of claim 20.

22. The fiber optic system of claim 20, wherein at least one of said single mode or few-mode input fiber and said fiber of claim 1 is rare-earth doped and configured as a gain fiber to amplify a pulse being propagated therein.

23. A fiber optic amplifier system comprising:

an optical pulse source providing optical pulses having a nearly diffraction limited input spatial profile;

an optical pump source; and

the fiber of claim 1, wherein at least a portion of said core region is rare-earth doped, said fiber further comprising a pump cladding configured to receive pump energy from said optical pump source, and a pump guide to transmit a portion of said received pump energy to said core region, said fiber configured to receive said pulses and amplify said 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.

24. The fiber optic amplifier system of claim 23, wherein a repetition rate of said output pulses exceeds about 1 kHz.

25. The fiber optic amplifier of claim 23, wherein a pulse width of the at least one output pulse is below about 1 ns.

26. A laser-based material processing system comprising:

the fiber optic amplifier system of claim 23; and

an optical system comprising a beam delivery optic to produce a spot on or within a material, said spot having a spot diameter in a range from about 1 μ

m to about 250 μ

m.

27. An all-glass photonic crystal fiber (PCF) comprising a core region, and N≧

3 layers of low-index features surrounding said core region, said PCF configured to propagate and guide a fundamental mode substantially within a region bounded by said core region.

28. The all-glass PCF of claim 27, wherein N=3.

29. The all-glass PCF of claim 27, wherein a diameter of said core region is less than about 150 μ

m, and a diameter of said PCF is about 700 μ

m or less.

30. The all-glass PCF of claim 27, wherein said low index features comprise fluorine doped glass.