Microstructured Optical Fibre Having A Large Core And A Flattened Fundamental Mode, Production Method Thereof And Use Of Same In Laser Microfabrication

• US 20140233900A1
• Filed: 09/18/2012
• Published: 08/21/2014
• Est. Priority Date: 09/20/2011
• Status: Active Grant

• Current Assignee: Centre National De La Recherche Scientifique, Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission), Université Lille 1, Sciences et Technologies
• Original Assignee: Centre National De La Recherche Scientifique, Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission), Université Lille 1, Sciences et Technologies
• Inventors: Mussot, Arnaud, Quiquempois, Yves, Bigot, Laurent, Hugonnot, Emmanuel, Lago, Laure, Bouwmans, Graud, Valentin, Constance
• Granted Patent: US 9,244,219 B2
• Time in Patent Office: Days
• US Class Current: 385/123
• CPC Class Codes: C03B 2201/02 Pure silica glass, e.g. pure fused quartz
• CPC Class Codes: C03B 2201/31 doped with germanium
• CPC Class Codes: C03B 2201/36 doped with rare earth metals and aluminium, e.g. Er-Al co-doped
• 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 2203/22 Radial profile of refractive index, composition or softening point
• 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 6/02314 Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
• 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 6/02347 Longitudinal structures arranged to form a regular periodic lattice, e.g. triangular, square, honeycomb unit cell repeated throughout cladding
• 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 6/02361 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 6/0238 Longitudinal structures having higher refractive index than background material, e.g. high index solid rods
• CPC Class Codes: G02B 6/032 with non solid core or cladding G02B6/02295 takes precedence
• CPC Class Codes: G02B 6/03611 Highest index adjacent to central axis region, e.g. annular core, coaxial ring, centreline depression affecting waveguiding
• CPC Class Codes: Y10T 29/49769 Using optical instrument [excludes mere human eyeballing]

Abstract

The fibre comprises a core (2) having an index N and diameter of 10 μm or more, surrounded by a ring (4) having an index N+Δn and thickness ΔR, and cladding (6) surrounding the ring and comprising for example air gaps (8). According to the invention: Δn≧10⁻³ and ΔR=α/(Δn)^β [1] where: 5×10⁻⁴ μm≦α≦5×10⁻² μm and 0.5≦β≦1.5. The numbers α and β are dependent on the wavelength λ of the light guided by the fibre, the number of missing gaps therein, the diameter d of the gaps, the spacing Λ thereof and N. To design the fibre, λ, the number of missing gaps, d/Λ, the core doping content, Λ0 and Δn are chosen; and ΔR is determined using equation [1] so as to obtain a flattened fundamental mode.

Claims

1. Microstructured optical fibre having a large core and a flattened fundamental mode, comprising:

a core wherein the diameter equals at least 10 μ

m,

a ring surrounding the core, wherein the optical index exceeds that of the core by a value Δ

n and wherein the outer radius exceeds the inner radius by a value Δ

R, and

an optical cladding surrounding the ring and comprising a matrix containing inclusions, for example longitudinal air gaps, wherein the optical index is different to that of the matrix, the equivalent mean optical index n_FSM of the cladding being less than the optical index of the core,

wherein Δ

n is greater than 10<sup>−

3</sup> and Δ

R is linked with Δ

n by the equation Δ

R=α

/(Δ

n)^β

where α

is in the interval ranging from 5×

10<sup>−

4</sup> μ

m to 5×

10⁻

μ

m, β

is in the interval ranging from 0.5 to 1.5 and α and

β

are dependent on the wavelength λ

of the light to be guided by the microstructured optical fibre, the number of missing inclusions therein, the diameter d of the inclusions, the spacing Λ

thereof and the optical index of the core.

2. Microstructured optical fibre according to claim 1, wherein the number of missing inclusions is equal to 7.

3. Microstructured optical fibre according to claim 1, wherein the core is not doped.

4. Microstructured optical fibre according to claim 3, wherein the core is made of non-doped silica, β

equals 1 and α

is given by the following formula;

α

a=2.489×

10<sup>−

2</sup>(d/Λ

)^0.25λ

²/Λ

where α

is expressed in micrometres when d, Λ and

λ

are also expressed as such.

5. Microstructured optical fibre according to claim 1, wherein the core is doped.

6. Microstructured optical fibre according to claim 5, wherein the core is made of silica doped, for example with ytterbium and aluminium or another codopant such as phosphorus or germanium, so as to increase the optical index of pure silica by approximately 1.5×

10<sup>−

3</sup>, β

equals 0.905 and α

is given by the following formula;

α

a=1.046×

10<sup>−

2</sup>(λ

/Λ

)^0.19

where α

is expressed in micrometres when Λ and

λ

are also expressed as such.

7. Microstructured optical fibre according to claim 5, wherein the core is made of silica doped, for example with ytterbium and aluminium or another codopant such as phosphorus or germanium, so as to increase the optical index of pure silica by approximately 5×

10<sup>−

3</sup>, β

equals 0.87 and α

is given by the following formula;

α

a=1.327×

10<sup>−

2</sup>(λ

/Λ

)^0.05

where α

is expressed in micrometres when Λ and

λ

are also expressed as such.

8. Method for producing the microstructured optical fibre having a large core and a flattened fundamental mode wherein the core diameter equals at least 10 μ

m, and a ring surrounding the core, wherein the optical index exceeds that of the core by a value Δ

n and wherein the outer radius exceeds the inner radius by a value Δ

R, and an optical cladding surrounding the ring, and a matrix containing inclusions wherein the optical index is different to that of the matrix, the equivalent mean optical index nFSM of the cladding being less than the optical index of the core, comprising the steps of;

choosing the λ

values;

choosing the number of missing inclusions;

choosing the ratio d/Λ

;

choosing the doping content T of the core with T being greater than or equal to 0;

choosing the Λ

values;

choosing the Δ

n values;

determining Δ

R using said equation so as to obtain a flattened fundamental mode at the fibre output when light having a wavelength λ

is injected at the input thereof; and

producing the microstructured optical fibre with the number of inclusions and parameters d, T, Λ

, Δ

n thus chosen, and the parameter Δ

R determined in this way.

9. Laser microfabrication method, wherein the microstructured optical fibre according to claim 8 is used for guiding the light emitted by the laser.