Optical waveguide

• US 7,321,712 B2
• Filed: 06/20/2005
• Issued: 01/22/2008
• Est. Priority Date: 12/20/2002
• Status: Active Grant

• Current Assignee: Crystal Fibre A/S (NKT A/S)
• Original Assignee: Crystal Fibre A/S (NKT A/S)
• Inventors: Sabert, Hendrik, Birks, Timothy Adam, Roberts, Peter John, Williams, David Philip, Onischenko, Alexander, Russell, Philip St. John
• Primary Examiner(s): Font; Frank F.
• Assistant Examiner(s): LEPISTO, RYAN A
• Application Number:
  US11/155,648
• Publication Number:
  US 20050276556A1
• Time in Patent Office: 946 Days
• Field of Search: 385/125
• US Class Current: 385/125
• 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 2203/42 Photonic crystal fibres, e.g. fibres using the photonic bandgap PBG effect, microstructured or holey optical fibres
• CPC Class Codes: C03B 2205/08 Sub-atmospheric pressure applied, e.g. vacuum
• CPC Class Codes: C03B 37/0122 for making preforms of photonic crystal, microstructured or holey optical fibres
• CPC Class Codes: C03B 37/0124 Means for reducing the diameter of rods or tubes by drawing, e.g. for preform draw-down
• CPC Class Codes: C03B 37/0126 Means for supporting, rotating, translating the rod, tube or preform
• CPC Class Codes: C03B 37/02781 Hollow fibres, e.g. holey fibres
• CPC Class Codes: G02B 6/02328 Hollow or gas filled core
• 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 6/02371 Cross section of longitudinal structures is non-circular
• CPC Class Codes: G02B 6/02385 Comprising liquid, e.g. fluid filled holes
• CPC Class Codes: Y02P 40/57 Improving the yield, e-g- reduction of reject rates

Abstract

An elongate waveguide for guiding light includes a core having an elongate region of relatively low refractive index; a microstructured region around the core having elongate regions of relatively low refractive index interspersed with elongate regions of relatively high refractive index; and a boundary at the interface between the core and the microstructured region, the boundary including in the transverse cross-section, a region of relatively high refractive index, which is connected to the microstructured region at a plurality of nodes, at least one relatively enlarged region around the boundary (and excluding a boundary having twelve nodes and six enlarged regions substantially at a mid-point between six pairs of relatively more-widely-spaced apart neighboring nodes).

Claims

1. An elongate waveguide for guiding light comprising:

a core comprising an elongate region of relatively low refractive index;

a microstructured region around the core comprising elongate regions of relatively low refractive index interspersed with elongate regions of relatively high refractive index, said microstructured region comprising a photonic band-gap structure; and

a boundary at the interface between the core and the microstructured region, said boundary region has a shape such that, in use, light guided by the waveguide is guided in a transverse mode in which, in the transverse cross-section, more than 95% of the guided light is in the regions of relatively low refractive index in the waveguide and such that the light is guided in a transverse mode providing an F-factor of less than 0.7 Λ

<sup>−

1</sup>, the boundary comprising, in the transverse cross-section, a region of relatively high refractive index, which is connected to the microstructured region at a plurality of nodes, at least one relatively enlarged region around the boundary; and

wherein the boundary fulfills at least one of the conditions selected from the group consisting of a) the boundary has twelve nodes and at least one enlarged region substantially at a mid-point between a pair of relatively less-widely-spaced apart neighboring nodes,

b) the boundary has less than six enlarged regions substantially at a mid-point between six pairs of relatively more-widely-spaced apart neighboring nodes or more than six enlarged regions substantially at a mid-point between six pairs of relatively more-widely-spaced apart neighboring nodes, and

c) the boundary has less than twelve nodes or more than twelve nodes.

2. A waveguide as claimed in claim 1, in which the boundary region has a shape such that, in use, light guided by the waveguide is guided in a transverse mode in which, in the transverse cross-section, more than 1% of the guided light is in the regions of relatively low refractive index in the photonic bandgap structure.

3. A waveguide as claimed in claim 1, in which the boundary region has a shape such that, in use, light guided by the waveguide is guided in a transverse mode in which, in the transverse cross-section, more than 50% of the guided light is in the region of relatively low refractive index in the core.

4. A waveguide as claimed in claim 1, in which the boundary region has a shape such that, in use, light guided by the waveguide is guided in a transverse mode providing an F-factor of less than 0.23 μ

m<sup>−

1</sup> (0.7 Λ

<sup>−

1</sup>).

5. A waveguide as claimed in claim 1, in which the core has, in the transverse cross-section, an area that is significantly greater than the area of at least some of the relatively low refractive index regions of the photonic bandgap structure, such as, an area that is greater than twice the area of at least some of the relatively low refractive index regions of the photonic bandgap structure.

6. A waveguide as claimed in claim 1, in which the relatively low refractive index regions make up more than 90% by volume of the photonic bandgap structure.

10. A waveguide as claimed in any one of claims 1, or 7, in which the boundary region comprises, in the transverse cross-section, a plurality of relatively high refractive index boundary veins joined end-to-end around the boundary between boundary nodes, each boundary vein being joined between a leading boundary node and a following boundary node, and each boundary node being joined between two boundary veins and to a relatively high refractive index region of the microstructured region, and in which at least one of the boundary veins comprises, along its length or at its end, an enlarged region that takes the form of a nodule.

11. A waveguide as claimed in claim 10, in which the nodule has a substantially elliptical shape in the transverse cross-section, such that an ellipse having a major axis of length L and a minor axis of length W substantially fits to the shape of the nodule in the transverse cross-section.

12. A waveguide as claimed in claim 11, in which the major axis extends along the boundary vein in which the nodule is comprised.

13. A waveguide as claimed in claim 11, in which the lengths W, L of the minor and major axes, respectively, have a mutual relation to each other selected from the group of relations consisting of

$W\le$

0.467 ⁢

L , W ≈

L 3 , W ≥

0.238 ⁢

L .

14. A waveguide as claimed in claim 11, arranged to guide light at a wavelength λ

₁, which is in the ultraviolet, visible or infrared parts of the electromagnetic spectrum.

15. A waveguide as claimed in claim 14, there being a parameter X that is equal to the wavelength λ

₁ in which the mutual relationships between parameters W, L, X are selected from the group of relationships consisting of

$L\ge <br><br>\frac{5<br><br>X}{12},L\approx <br><br>\frac{X}{2},L\le <br><br>\frac{7<br><br>X}{12},W><br><br>\frac{X}{18},W><br><br>\frac{5<br><br>X}{36},W\approx <br><br>\frac{X}{6},<br><br>W\le <br><br>\frac{7<br><br>X}{36},L\times <br><br>W\ge <br><br>0.058<br><br>X^2,L\times <br><br>W\approx <br><br>\frac{X^2}{12},L\times <br><br>W\le <br><br>0.113<br><br>X^2,<br><br>W\le <br><br>\left(\frac{1}{18}+\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(-\frac{1}{18}+\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(\frac{5}{18}-\frac{L}{3}\right)<br><br>X,<br><br>W\le <br><br>\left(\frac{7}{18}-\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(-0.133+0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.095+0.238<br><br>L\right)<br><br>X,W\ge <br><br>\left(0.333-0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.333-0.238<br><br>L\right)<br><br>X,W\le <br><br>\left(0.467-0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.238-0.238<br><br>L\right)<br><br>X.$

16. A waveguide as claimed in claim 11, arranged to guide light at a wavelength λ

₂, wherein light guided at the wavelength λ

₂ exhibits lower loss than light guided in the waveguide at any other wavelength.

17. A waveguide as claimed in claim 16, there being a parameter X that is equal to the wavelength λ

₂ in which the mutual relationships between parameters W, L, X are selected from the group of relationships consisting of

$L\ge <br><br>\frac{5<br><br>X}{12},L\approx <br><br>\frac{X}{2},L\le <br><br>\frac{7<br><br>X}{12},W><br><br>\frac{X}{18},W><br><br>\frac{5<br><br>X}{36},W\approx <br><br>\frac{X}{6},<br><br>W\le <br><br>\frac{7<br><br>X}{36},L\times <br><br>W\ge <br><br>0.058<br><br>X^2,L\times <br><br>W\approx <br><br>\frac{X^2}{12},L\times <br><br>W\le <br><br>0.113<br><br>X^2,<br><br>W\le <br><br>\left(\frac{1}{18}+\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(-\frac{1}{18}+\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(\frac{5}{18}-\frac{L}{3}\right)<br><br>X,<br><br>W\le <br><br>\left(\frac{7}{18}-\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(-0.133+0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.095+0.238<br><br>L\right)<br><br>X,W\ge <br><br>\left(0.333-0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.333-0.238<br><br>L\right)<br><br>X,W\le <br><br>\left(0.467-0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.238-0.238<br><br>L\right)<br><br>X.$

18. A waveguide as claimed in claim 11, wherein the microstructured region may comprise a substantially periodic array of elements characterized by a unit cell and a pitch Λ

, there being a parameter X that is equal to the pitch Λ

in which the mutual relationships between parameters W, L, X are selected from the group of relationships consisting of

$L\ge <br><br>\frac{5<br><br>X}{12},L\approx <br><br>\frac{X}{2},L\le <br><br>\frac{7<br><br>X}{12},W><br><br>\frac{X}{18},W><br><br>\frac{5<br><br>X}{36},W\approx <br><br>\frac{X}{6},<br><br>W\le <br><br>\frac{7<br><br>X}{36},L\times <br><br>W\ge <br><br>0.058<br><br>X^2,L\times <br><br>W\approx <br><br>\frac{X^2}{12},L\times <br><br>W\le <br><br>0.113<br><br>X^2,<br><br>W\le <br><br>\left(\frac{1}{18}+\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(-\frac{1}{18}+\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(\frac{5}{18}-\frac{L}{3}\right)<br><br>X,<br><br>W\le <br><br>\left(\frac{7}{18}-\frac{L}{3}\right)<br><br>X,W\ge <br><br>\left(-0.133+0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.095+0.238<br><br>L\right)<br><br>X,W\ge <br><br>\left(0.333-0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.333-0.238<br><br>L\right)<br><br>X,W\le <br><br>\left(0.467-0.467<br><br>L\right)<br><br>X,<br><br>W\le <br><br>\left(0.238-0.238<br><br>L\right)<br><br>X.$

19. A waveguide according to claim 11, wherein the minor axis extends substantially radially with respect to the center of the waveguide.

20. A waveguide according to claim 10, wherein there are plural groups of two or more enlarged regions and the groups are substantially equi-spaced around the boundary.

21. A waveguide according to claim 10, wherein a plurality of enlarged regions are positioned along veins and spaced apart from any nodes.

22. A waveguide according to claim 10, wherein an enlarged region comprises a relatively thick vein, compared to the thickness of at least one other vein, extending between a pair of neighboring nodes.

23. A waveguide according to claim 10, wherein an enlarged region is coincident with a node such that the node has an uncharacteristic form relative to the photonic band-gap cladding.

24. A waveguide according to claim 10, wherein said nodule has a major dimension and the length of the major dimension is at least 0.42 times the distance between the two adjacent nodes on either side of the enlarged region and the length of the major dimension is less than 0.98 times the distance between the two adjacent nodes.

25. A waveguide according to claim 10, wherein said nodule has a major dimension and the major dimension is at least 0.42 times a characteristic pitch of the microstructured region and the major dimension is less than 0.98 times said characteristic pitch.

28. A waveguide according to any one of claims 1 or 7, wherein there are more than six enlarged regions around the boundary, such as twelve or more enlarged regions around the boundary, such as eighteen enlarged regions around the boundary.

29. A waveguide according to any one of claims 1 or 7, wherein the boundary has no more than two fold rotational symmetry about any longitudinal axis thereof at least in part by virtue of the presence or placement of the or each relatively enlarged region.

30. A waveguide according to claim 29, wherein the boundary has only two fold rotational symmetry.

31. A waveguide as claimed in any one of claims 1 or 7, in which the boundary region comprises, in the transverse cross-section, a plurality of relatively high refractive index boundary veins joined end-to-end around the boundary between boundary nodes, each boundary vein being joined between a leading boundary node and a following boundary node, and each boundary node being joined between two boundary veins and to a relatively high refractive index region of the microstructured region, and in which at least one of the boundary veins comprises, along its length or at its end, an enlarged region that takes the form of a nodule, said nodule having a substantially elliptical shape in the transverse cross-section, such that an ellipse having a major axis of length L and a minor axis of length W substantially fits to the shape of the nodule in the transverse cross-section in which the lengths of the minor and major axes are substantially equal, that is W˜

L.

7. An elongate waveguide for guiding light comprising:

a core comprising an elongate region of relatively low refractive index; and

a microstructured region comprising a photonic bandgap structure arranged to provide a photonic bandgap over a range of wavelengths of light, the microstructured region comprising elongate regions of relatively low refractive index interspersed with elongate regions of relatively high refractive index, including a boundary region of relatively high refractive index that surrounds, in a transverse cross-section of the waveguide, the core;

wherein the boundary region has a shape such that, in use, light guided by the waveguide is guided in a transverse mode in which, in the transverse cross-section, more than 95% of the guided light is in the regions of relatively low refractive index in the waveguide and such that the light is guided in a transverse mode providing an F-factor of less than 0.7 Λ

<sup>−

1</sup>.

8. A waveguide as claimed in claim 7, in which the boundary region has a shape such that, in use, light guided by the waveguide is guided in a transverse mode in which, in the transverse cross-section, more than 1% of the guided light is in the regions of relatively low refractive index in the photonic bandgap structure.

9. A waveguide as claimed in claim 7, in which the boundary region has a shape such that, in use, light guided by the waveguide is guided in a transverse mode in which, in the transverse cross-section, more than 50% of the guided light is in the region of relatively low refractive index in the core.

26. A waveguide as claimed in claim 7, in which the core has, in the transverse cross-section, an area that is significantly greater than the area of at least some of the relatively low refractive index regions of the photonic bandgap structure, such as, an area that is greater than twice the area of at least some of the relatively low refractive index regions of the photonic bandgap structure.

27. A waveguide as claimed in claim 7, in which the relatively low refractive index regions make up more than 90% by volume of the photonic bandgap structure.

32. An elongate waveguide for guiding light comprising:

a core comprising an elongate region of relatively low refractive index;

a microstructured region around the core comprising elongate regions of relatively low refractive index interspersed with elongate regions of relatively high refractive index, said microstructured region comprising a photonic band-gap structure; and

a boundary at the interface between the core and the microstructured region said boundary region has a shape such that, in use, light with a wavelength λ

guided by the waveguide is guided in a transverse mode in which, in the transverse cross-section, more than 95% of the guided light is in the regions of relatively low refractive index in the waveguide and such that the light is guided in a transverse mode providing an F-factor of less than a value, said value being 0.23 μ

m<sup>−

1</sup> when calculated for λ

=1550 nm, the boundary comprising, in the transverse cross-section, a region of relatively high refractive index, which is connected to the microstructured region at a plurality of nodes, at least one relatively enlarged region around the boundary; and

wherein the boundary fulfills at least one of the conditions selected from the group consisting of a) the boundary has twelve nodes and at least one enlarged region substantially at a mid-point between a pair of relatively less-widely-spaced apart neighboring nodes,

b) the boundary has less than six enlarged regions substantially at a mid-point between six pairs of relatively more-widely-spaced apart neighboring nodes or more than six enlarged regions substantially at a mid-point between six pairs of relatively more-widely-spaced apart neighboring nodes, and

c) the boundary has less than twelve nodes or more than twelve nodes.