Rare earth doped and large effective area optical fibers for fiber lasers and amplifiers

• US 8,542,968 B2
• Filed: 06/11/2012
• Issued: 09/24/2013
• Est. Priority Date: 09/20/2006
• Status: Expired due to Fees

• Current Assignee: IMRA America Incorporated (Aisin Corp.)
• Original Assignee: IMRA America Incorporated (Aisin Corp.)
• Inventors: Dong, Liang, Peng, Xiang
• Primary Examiner(s): KIM, ELLEN E
• Application Number:
  US13/493,264
• Publication Number:
  US 20120250143A1
• Time in Patent Office: 470 Days
• Field of Search: 385/123, 385/124, 385126-128, 385/141, 385/142, 385/144, 359/341.3
• US Class Current: 385/124
• CPC Class Codes: C03B 2201/10 doped with boron C03B2201/14 takes precedence
• CPC Class Codes: C03B 2201/28 doped with phosphorus
• CPC Class Codes: C03B 2201/34 doped with rare earth metals, i.e. with Sc, Y or lanthanides, e.g. for laser-amplifiers
• CPC Class Codes: C03B 2203/14 Non-solid, i.e. hollow products, e.g. hollow clad or with core-clad interface
• CPC Class Codes: C03B 2203/23 Double or multiple optical cladding profiles
• CPC Class Codes: C03B 2203/30 Polarisation maintaining [PM], i.e. birefringent products, e.g. with elliptical core, by use of stress rods, "PANDA" type fibres
• CPC Class Codes: C03B 2203/42 Photonic crystal fibres, e.g. fibres using the photonic bandgap PBG effect, microstructured or holey optical fibres
• CPC Class Codes: C03B 37/01217 for making preforms of polarisation-maintaining optical fibres polarisation-maintaining optical fibres per se G02B6/105
• CPC Class Codes: C03B 37/0122 for making preforms of photonic crystal, microstructured or holey optical fibres
• CPC Class Codes: C03B 37/01838 for delivering and depositing additional reactants as liquids or solutions, e.g. for solution doping of the deposited glass
• CPC Class Codes: C03C 13/046 Multicomponent glass compositions
• CPC Class Codes: C03C 2201/10 containing boron C03C2201/14 takes precedence
• CPC Class Codes: C03C 2201/28 containing phosphorus
• CPC Class Codes: C03C 2201/34 containing rare earth metals C03C2201/36 takes precedence
• CPC Class Codes: C03C 2201/3488 Ytterbium
• CPC Class Codes: C03C 3/06 with more than 90% silica by weight, e.g. quartz C03C3/045 takes precedence
• CPC Class Codes: C03C 3/097 containing phosphorus, niobium or tantalum
• CPC Class Codes: C03C 4/0071 for laserable glass
• CPC Class Codes: G02B 6/024 with polarisation maintaining properties
• CPC Class Codes: G02B 6/032 with non solid core or cladding G02B6/02295 takes precedence
• CPC Class Codes: G02B 6/03616 : Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
• CPC Class Codes: G02B 6/03622 : having 2 layers only
• CPC Class Codes: G02B 6/03633 : arranged - -
• CPC Class Codes: G02B 6/03638 : having 3 layers only
• CPC Class Codes: H01S 3/06712 : Polarising fibre; Polariser
• CPC Class Codes: H01S 3/06716 : Fibre compositions per se C03C13/04or doping with active elements lasing materials in general H01S3/14
• CPC Class Codes: H01S 3/06741 : Photonic crystal fibre, i.e. the fibre having a photonic bandgap
• CPC Class Codes: H01S 3/06754 : Fibre amplifiers H01S3/06708 takes precedence
• CPC Class Codes: H01S 3/094007 : Cladding pumping, i.e. pump light propagating in a clad surrounding the active core
• CPC Class Codes: H01S 3/1618 : ytterbium

Abstract

Various embodiments described herein include rare earth doped glass compositions that may be used in optical fiber and rods having large core sizes. Such optical fibers and rods may be employed in fiber lasers and amplifiers. The index of refraction of the glass may be substantially uniform and may be close to that of silica in some embodiments. Possible advantages to such features include reduction of formation of additional waveguides within the core, which becomes increasingly a problem with larger core sizes.

Claims

1. A large-core optical fiber comprising:

a core having a core radius ρ and

a core index of refraction n_core, wherein said core comprises a doped region having an area of at least 200 μ

m square;

a first cladding disposed about said core, said first cladding having an outer radius ρ

₁ and an index of refraction n_c1, said core and said first cladding having a difference in index of refraction Δ

n=n_core−

n_c1; and

a second cladding disposed about said first cladding, said first cladding and said second cladding having a difference in index of refraction Δ

n₁,

wherein the first cladding radius, ρ

₁, is greater than about 1.1ρ and

less than about 2ρ

, and the refractive index difference between said first cladding and said second cladding, Δ

n₁, is greater than about 1.5Δ

n and less than about 50Δ

n.

2. The large-core optical fiber of claim 1, said large-core optical fiber being bendable and configured with a reduced bend loss relative to a large-core optical fiber having substantially the same core radius, ρ

, and refractive index difference between cladding and core, Δ

n.

3. The large-core optical fiber of claim 1, wherein Δ

n is less than about 10<sup>−

3</sup>.

4. The large-core optical fiber of claim 1, wherein said core is as large as about 50 μ

m and said Δ

n is less than about 8×

10<sup>−

5</sup>.

5. The large-core optical fiber of claim 1, wherein said core is as large as about 50 μ

m.

6. The large-core optical fiber of claim 1, wherein said large-core optical fiber comprises a step-index fiber.

7. The large-core optical fiber of claim 1, wherein said first cladding has a numerical aperture (NA) less than about 0.05, said NA determined by n_core and n_c1.

8. The large-core optical fiber of claim 1, wherein said core comprises a doped region having an average refractive index within about ±

0.003 or less of the refractive index of silica.

9. The large-core optical fiber of claim 1, wherein said first cladding is slightly larger than said core and said first cladding radius, ρ

₁, is in the range 1.1ρ

<

ρ

₁<

1.5ρ

.

10. The large-core optical fiber of claim 1, wherein 1.5Δ

n<

Δ

n₁<

10Δ

n.

11. The large-core optical fiber of claim 1, wherein said core is partially rare earth doped.

12. The large-core optical fiber of claim 1, wherein said core is entirely rare earth doped.

13. The large-core optical fiber of claim 1, wherein said core radius is as large as about 25 μ

m.

14. The large-core optical fiber of claim 1, further comprising a third cladding disposed about said second cladding, and a pump propagation region comprising said core, said first cladding, and said second cladding.

15. The large-core optical fiber of claim 1, further comprising a coating, and an additional cladding disposed between said coating and said second cladding to form a pump guide.

16. The large-core optical fiber of claim 1, wherein said core has an effective refractive index uniformity with less than about 5×

10<sup>−

4</sup> maximum peak-to-peak variation.

17. The large-core optical fiber of claim 1, wherein said large-core optical fiber is polarization maintaining.

18. The large-core optical fiber of claim 1, wherein said second cladding comprises holes that are configured to provide leakage channels such that said large-core optical fiber supports one or a few modes and higher order modes are leaked.

19. The large-core optical fiber of claim 1, wherein a portion of said large-core optical fiber comprises holey fiber.

20. The large-core optical fiber of claim 1, wherein said core comprises:

silica having a refractive index;

at least about 10 mol % phosphorus in said silica;

at least about 10 mol % boron in said silica;

rare earth ions in said silica, said rare earth ions having a concentration in said silica of at least about 1000 mol ppm,

wherein said silica having said phosphorus, said boron, and said rare earth ions therein has a refractive index within about ±

0.003 or less of the refractive index of the silica.

21. An optical fiber system for providing optical amplification, the optical fiber system comprising:

the large-core optical fiber of claim 1, wherein said core of said large-core fiber is doped with one or more types of rare earth ions, said large-core optical fiber comprising a combined waveguide formed by said core and said first cladding layer;

an optical pump optically coupled to said large-core optical fiber; and

an optical source optically coupled to an input of said large-core optical fiber.

22. The optical fiber system of claim 21, wherein said combined waveguide is configured such that a mode supported in said core has increased gain relative to a mode having substantial power in said first cladding.

23. The optical fiber system of claim 21, wherein said core is configured to receive an input beam launched in said core, wherein said input beam is in a fundamental mode of said large-core optical fiber.

24. The optical fiber system of claim 21, wherein said large-core optical fiber is configured to support 1 to 10 modes in said core.

25. The optical fiber system of claim 21, wherein values of said first cladding radius ρ

₁ and said Δ

n are such that the number of modes supported in said combined waveguide and inter-mode coupling among the number of supported modes are limited such that a mode supported in said core has increased gain relative to a mode having substantial power in said first cladding.

26. The optical fiber system of claim 21, said core having substantial refractive index uniformity.

27. The optical fiber system of claim 21, wherein said core radius is as large as about 25 μ

m.

28. The optical fiber system of claim 21, wherein a portion of said large-core optical fiber comprises holey fiber.

29. The optical fiber system of claim 21, wherein said large-core optical fiber is bendable and configured with a reduced bend loss relative to a large-core optical fiber having substantially the same core radius, ρ

, and refractive index difference between cladding and core, Δ

n.

30. The optical fiber system of claim 21, wherein said large-core optical fiber further comprises a third cladding disposed about said second cladding, and a pump propagation region comprising said core, said first cladding, and said second cladding.

31. The large-core optical fiber of claim 21, further comprising a coating, and an additional cladding disposed between said coating and said second cladding to form a pump guide.

32. The optical fiber system of claim 21, wherein said first cladding is slightly larger than said core and said first cladding radius, ρ

₁, is in the range 1.1ρ

<

ρ

₁<

1.5ρ

.

33. The optical fiber system of claim 21, wherein said input of said large-core optical fiber is tapered, said large-core optical fiber has a length extending from said tapered input, and said tapered input supports a reduced number of optical modes than the length extending from said tapered input.

34. The optical fiber system of claim 21, wherein said core of said large-core optical fiber comprises:

silica having a refractive index;

at least about 10 mol % phosphorus in said silica;

at least about 10 mol % boron in said silica;

rare earth ions in said silica, said rare earth ions having a concentration in said silica of at least about 1000 mol ppm,

wherein said silica having said phosphorus, said boron, and said rare earth ions therein has a refractive index within about ±

0.003 or less of the refractive index of the silica.

35. The optical fiber system of claim 34, wherein said large-core optical fiber has a pump absorption in a range from 300 to 1500 dB/m.