Large core area single mode optical fiber

• US 8,903,214 B2
• Filed: 06/27/2011
• Issued: 12/02/2014
• Est. Priority Date: 06/25/2010
• Status: Active Grant

• Current Assignee: NKT Photonics A/S (Hamamatsu Photonics KK)
• Original Assignee: NKT Photonics A/S (Hamamatsu Photonics KK)
• Inventors: Alkeskjold, Thomas Tanggaard
• Primary Examiner(s): Diacou, Ari M
• Application Number:
  US13/805,869
• Publication Number:
  US 20130114129A1
• Time in Patent Office: 1,254 Days
• US Class Current: 385/126
• 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 2203/12 Non-circular or non-elliptical cross-section, e.g. planar core
• 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 2203/28 Large core fibres, e.g. with a core diameter greater than 60 micrometers
• CPC Class Codes: C03B 2203/29 Segmented core 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 37/0122 for making preforms of photonic crystal, microstructured or holey optical fibres
• CPC Class Codes: G02B 6/02019 Effective area greater than 90 square microns in the C band, i.e. 1530-1565 nm
• CPC Class Codes: G02B 6/02333 Core having higher refractive index than cladding, e.g. solid core, effective index guiding
• CPC Class Codes: G02B 6/02338 Structured core, e.g. core contains more than one material, non-constant refractive index distribution in core, asymmetric or non-circular elements in core unit, multiple cores, insertions between core and clad
• CPC Class Codes: G02B 6/02352 Complex periodic lattices or multiple interpenetrating periodic lattices, e.g. unit cell having more than two materials, partially internally coated holes, for multiple bandgaps
• 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 6/0283 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: H01S 3/06733 Fibre having more than one cladding
• 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 3/08045 Single-mode emission
• CPC Class Codes: H01S 3/094007 Cladding pumping, i.e. pump light propagating in a clad surrounding the active core

Abstract

A single-mode optical fiber for guiding an optical signal, wherein the core region is capable of guiding an optical signal in a fundamental core mode at an optical signal wavelength. A cladding region is arranged to surround the core region and includes an inner cladding region and an outer cladding region. The inner cladding region includes a background material and a plurality of inner cladding features arranged in the background material, wherein a plurality of the plurality of inner cladding features are of a first type of feature that includes an air hole surrounded by a high-index region comprising a high-index material that is larger than the refractive index of the inner cladding background material.

Claims

1. A single-mode optical fiber for guiding an optical signal, said optical fiber having a longitudinal, optical axis and a cross section perpendicular thereto, said optical fiber comprising:

a core region being capable of guiding an optical signal in a fundamental core mode with an effective refractive index, n_c, at an optical signal wavelength, λ

₁;

a cladding region surrounding the core region, the cladding region comprising an inner cladding region and an outer cladding region, said inner cladding region comprising a background material having a refractive index, n_b, and a plurality of inner cladding features arranged in said background material, wherein at least a plurality of said plurality of inner cladding features are of a first type of feature, said first type of feature comprising an air hole surrounded by a high-index region comprising a high-index material having a refractive index, n_r, that is larger than the refractive index of the inner cladding background material, said first type of feature supports an optical mode with an effective refractive index, n₁, which is lower than or equal to the effective refractive index of the fundamental core mode, n_c, at said optical signal wavelength, λ

₁,

wherein said core region has a maximum cross-sectional dimension of more than about 40 μ

m,

and wherein the index difference between the high-index material and the background material of the inner cladding is below about 1.10<sup>−

2</sup>.

2. The optical fiber according to claim 1, wherein said plurality of inner cladding features further comprises a second type of feature comprising an air hole in direct contact with the background material having a refractive index, n_b.

3. The optical fiber according to claim 1, wherein said plurality of inner cladding features are substantially round.

4. The optical fiber according to claim 1, the fiber being capable of being cladding pumped or core pumped and being adapted for amplifying an optical signal, the core region comprising a material doped with at least one active element;

and the inner cladding region being capable of guiding a pump signal at a pump wavelength, λ

_p.

5. The optical fiber according to claim 1, wherein the core region has a core effective refractive index, the core effective refractive index being substantially equal to the refractive index of the inner cladding background material.

6. The optical fiber according to claim 4, wherein the material doped with an active element is substantially arranged in an active part of said core region, said active part surrounding a central part of said core region, such as said active part being substantially formed by a cross sectional annular region surrounding the central part of the core region and wherein said active part is arranged so that the fundamental core mode has a modal field overlap with the active part, which is below about 50%.

7. The optical fiber according to claim 1, wherein said core region is doped with one or more materials selected from the group of Fluorine (F), Germanium (Ge), and Cerium (Ce), or combinations of these.

8. The optical fiber according to claim 1, wherein said inner cladding features are arranged in a substantially periodic lattice with periodicity, λ

, and wherein the periodicity, λ

, of said lattice is such that the ratio λ

/2 is more than about 5.

9. The optical fiber according to claim 8, wherein said inner cladding features are arranged in a substantially hexagonal lattice.

10. The optical fiber according to claim 8, wherein a diameter, d₁, of said air hole of said first type of feature is such that the d₁/Λ

ratio is below about 0.3.

11. The optical fiber according to claim 1, wherein said high-index region of said first type of feature comprises germanium doped silica.

12. The optical fiber according to claim 2, wherein said inner cladding features are arranged in a substantially hexagonal lattice and the six nearest neighbors surrounding a first type of feature are of said second type.

13. The optical fiber according to claim 1, wherein said first type of inner cladding feature is capable of supporting an optical mode, which at the optical signal wavelength, λ

₁, has an effective refractive index that is smaller than the effective refractive index of the fundamental core mode; and

which at a range of wavelengths shorter than the optical signal wavelength, λ

₁, has an effective refractive index that is larger than or equal to the effective refractive index of the fundamental core mode.

14. The optical fiber according to claim 1, wherein said fiber is a rod fiber.

17. An optical amplifier system for amplifying an optical signal at an optical signal wavelength, λ

₁, said system comprising

i. a single mode cladding pumped optical fiber according to claim 1;

ii. a pump light source capable of providing pump light at a pump wavelength, λ

_p said pump light source being optically coupled to said cladding pumped optical fiber; and

iii. a seed light source arranged to emit an optical signal into the core of said cladding pumped optical fiber.

15. A cladding pumped optical fiber for amplifying an optical signal, said optical fiber having a longitudinal, optical axis and a cross section perpendicular thereto, said optical fiber comprising:

a core region comprising a material doped with at least one active element;

said core region being capable of guiding an optical signal in a fundamental core mode with an effective refractive index, n_c, at an optical signal wavelength, λ

₁;

a cladding region surrounding the core region, the cladding region comprising an inner cladding region and an outer cladding region, the inner cladding region being capable of guiding a pump signal at a pump wavelength, λ

_p, said inner cladding region comprising a background material having a refractive index, n_b, and a plurality of inner cladding features arranged in said background material, wherein at least a plurality of said plurality of inner cladding features are of a first type of feature, said first type of feature comprising an air hole surrounded by a high-index region comprising a high-index material having a refractive index, n_r, that is larger than the refractive index of the inner cladding background material, said plurality of said first type of inner cladding feature being arranged to provide at least one cladding mode that suppresses higher order core modes.

16. A method for producing an optical fiber, said method comprising:

I. providing at least one core preform element, and a plurality of inner cladding preform elements;

II. arranging said core preform element and said inner cladding preform elements in a preform such that said inner cladding preform elements surround said core preform element, and optionally arranging a plurality of outer cladding preform elements and/or an outer cladding preform tube to surround the core preform element and the inner cladding preform elements;

III. drawing said preform to an optical fiber;

wherein said inner cladding preform elements comprise a plurality of a first type of preform elements comprising an air hole surrounded by a region with a higher index of refraction than the outer cladding preform elements.