Optical waveguide structure

• US 20040264902A1
• Filed: 06/20/2003
• Published: 12/30/2004
• Est. Priority Date: 06/20/2003
• Status: Active Grant

• Current Assignee: Quantum NIL Limited, Quantum NIL Limited Taiwan Branch
• Original Assignee: Mesophotonics Limited
• Inventors: Zoorob, Majd, Parker, Greg, Charlton, Martin
• Granted Patent: US 7,016,586 B2
• Time in Patent Office: Days
• US Class Current: 385/129
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 2006/12147 Coupler
• CPC Class Codes: G02B 6/02309 Structures extending perpendicularly or at a large angle to the longitudinal axis of the fibre, e.g. photonic band gap along fibre axis
• 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 6/02366 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 6/1225 comprising photonic band-gap structures or photonic lattices

Abstract

There is provided a planar waveguide structure (700) having a first core layer (708), a second core layer (704) and a cladding layer (706), wherein the cladding layer (706) is disposed between the first core layer (708) and the second core layer (704) to form an inter-core cladding layer (706). The inter-core cladding layer (706) comprises a first region (722) having a first refractive index and an array of sub-regions (724) formed therein having a second refractive index. The subregions (724) do not extend into either the first or the second core layer, and they give rise to a photonic band structure region, which is effective to perturb an evanescent field of an optical signal propagating through the core layers.

Claims

1. A planar waveguide structure having a first core layer, a second core layer and an inter-core cladding layer disposed between the first core layer and the second core layer, wherein the inter-core cladding layer comprises a first region having a first refractive index, n_inter, and an array of sub-regions formed therein having a second refractive index, n_sub, which do not extend into either the first or the second core layer, the array of sub-regions giving rise to a photonic band structure region, which is effective to perturb an evanescent field of an optical signal propagating through the core layers.

2. A waveguide structure as claimed in claim 1, wherein an effective mode index contrast acting upon the optical signal as the signal passes through the photonic band structure region is greater than 0.1 percent.

3. A waveguide structure as claimed in claim 1, wherein the first core layer has a first thickness and the second core layer has a second thickness, the first thickness being different from the second thickness, such that a field profile of an optical signal propagating through the core layers is asymmetric with respect to the core layers.

4. A waveguide structure as claimed in claim 1, wherein a clearance is provided in the inter-core cladding layer between the array of sub-regions and at least one of the core layers, such that the material of the sub-regions is spaced apart from the core layer at a pre-determined distance.

5. A waveguide structure as claimed in claim 1, wherein the first region is formed of a SiO₂ glass.

6. A waveguide structure as claimed in claim 1, wherein the sub-regions are air filled holes.

7. A waveguide structure as claimed in claim 1, wherein the sub-regions are formed from silicon.

8. A waveguide structure as claimed in claim 1, wherein the sub-regions are arranged in a one dimensional array.

9. A waveguide structure as claimed in claim 1, wherein the sub-regions are arranged in a two dimensional array.

10. A waveguide structure as claimed in claim 1, the structure further comprising a first outer cladding layer, the first outer cladding layer comprising a first outer cladding region having a third refractive index n_outer—

₁.

11. A waveguide structure as claimed in claim 10, wherein the first outer cladding layer further comprises an array of first outer cladding sub-regions having a fourth refractive index n_out—

<sub>sub—

1</sub>, which do not extend into the core layer, the array of first outer cladding sub-regions giving rise to a first outer cladding photonic band structure region, which is effective to perturb further the evanescent field of the optical signal propagating through the core layers.

12. A waveguide structure as claimed in claim 11, wherein effective mode index contrast acting upon the optical signal as the signal passes through the first outer cladding photonic band structure region is greater than 0.1 percent.

13. A waveguide structure as claimed in claim 11, wherein the first outer cladding region is formed of a SiO₂ glass.

14. A waveguide structure as claimed in claim 11, wherein the first outer cladding sub-regions are air filled holes.

15. A waveguide structure as claimed in claim 11, wherein the first outer cladding sub-regions are formed from silicon.

16. A waveguide structure as claimed in claim 11, wherein the first outer cladding sub-regions are arranged in a one dimensional array.

17. A waveguide structure as claimed in claim 11, wherein the first outer cladding sub-regions are arranged in a two dimensional array.

18. A waveguide structure as claimed in claim 10, wherein said first outer cladding layer is a buffer layer disposed adjacent to the first core layer at an opposite side of the first core layer from the inter-core cladding layer.

19. A waveguide structure as claimed in claim 10, wherein said first outer cladding layer is a capping layer disposed adjacent to the second core layer at an opposite side of the second core layer from the inter-core cladding layer.

20. A waveguide structure as claimed in claim 10, the structure further comprising a second outer cladding layer, the second outer cladding layer comprising a second outer cladding region having a fifth refractive index n_outer—

₂.

21. A waveguide structure as claimed in claim 20, the second outer cladding layer further comprising an array of second outer cladding sub-regions having a sixth refractive index n_out—

<sub>sub—

2</sub>, which do not extend into the core layer, the array of second outer cladding sub-regions giving rise to a second outer cladding photonic band structure region, which is effective to perturb further the evanescent field of the optical signal propagating through the core layers.

22. A waveguide structure as claimed in claim 21, wherein an effective mode index contrast acting upon the optical signal as the signal passes through the second outer cladding photonic band structure region is greater than 0.1 percent.

23. A waveguide structure as claimed in claim 21, wherein the second outer cladding region is formed of a SiO₂ glass.

24. A waveguide structure as claimed in claim 21, wherein the second outer cladding sub-regions are air filled holes.

25. A waveguide structure as claimed in claim 21, wherein the second outer cladding sub-regions are formed from silicon.

26. A waveguide structure as claimed in claim 21, wherein the second outer cladding sub-regions are arranged in a one dimensional array.

27. A waveguide structure as claimed in claim 21, wherein the second outer cladding sub-regions are arranged in a two dimensional array.

28. A waveguide structure as claimed in claim 20, wherein the inter-core cladding layer is formed of a first material, the first outer cladding layer is formed of a second material and the second outer cladding layer is formed of a third material, and wherein the first material has a higher refractive index than either the second material or the third material.

29. A waveguide structure as claimed in claim 28, wherein the first and second core layers are formed of a fourth and fifth material respectively and wherein the first material is different from the second, third, fourth and fifth materials.

30. A waveguide structure as claimed in claim 10, wherein a clearance is provided in the first outer cladding layer between the array of first outer cladding sub-regions and at least one of the core layers, such that the material of the first outer cladding sub-regions is spaced apart from the core layer at a pre-determined distance.

31. A waveguide structure as claimed in claim 30, wherein a clearance is provided in the second outer cladding layer between the second outer cladding sub-regions and at least one of the core layers, such that the material of the second outer cladding sub-regions is spaced apart from the core layer at a pre-determined distance.

32. A waveguide structure as claimed in claim 1, wherein the first core layer and the second core layer are formed from a diffused material.

33. A waveguide structure as claimed in claim 1, wherein the first core layer and the second core layer are formed from a graded material.

34. A waveguide structure as claimed in claim 1, wherein at least one of the first core layer and the second core layer is formed as a rib having a predetermined breadth.

35. A waveguide structure as claimed in claim 34, wherein the or each ribbed core is tapered from a first predetermined breadth to a second predetermined breadth, the second predetermined breadth being less than the first predetermined breadth.

36. A waveguide structure as claimed in claim 1, wherein both the first core layer and the second core layer are formed as ribs.

37. A waveguide structure as claimed in claim 1, wherein the array of sub-regions in the inter-core cladding layer extends beyond the breadth of the rib.

38. A waveguide structure as claimed in claim 1, the first core layer being provided with a pair of vertical sidewalls, each of the sidewalls extending from an edge of the first rib to a corresponding edge of the second rib, thereby forming a core with rectangular cross-section.

76. An optical device incorporating a waveguide structure as claimed in claim 1.

39. An annular waveguide structure having an annular core layer and an inner cladding layer, wherein the inner cladding layer is substantially surrounded by the annular core layer and wherein the inner cladding layer comprises a first region having a first refractive index, n_inner, and a one-dimensional array of sub-regions formed therein having a second refractive index, n_sub, which do not extend into the annular core layer, the array of sub-regions giving rise to a photonic band structure region, which is effective to perturb an evanescent field of an optical signal propagating through the core layer.

40. An annular waveguide structure as claimed in claim 39, further including an outer capping layer that substantially surrounds the annular core layer.

41. An annular waveguide structure as claimed in claim 39, wherein the inner cladding layer includes a number of longitudinal cavities, whereby the average first refractive index, n_inner, is tuned to a predetermined value.

42. An annular waveguide structure as claimed in claim 41, wherein the average first refractive index, n_inner, is substantially 1.

77. An optical device incorporating an annular waveguide structure as claimed in claim 39.

43. A planar waveguide structure having a first core layer, a second core layer, a first outer cladding layer, a second outer cladding layer and an inter-core cladding layer, the inter-core cladding layer being disposed between the first core layer and the second core layer and comprising a first region having a first refractive index, n_inter, and an array of sub-regions formed therein having a second refractive index, n_sub, which do not extend into the core layer, the array of sub-regions giving rise to a photonic band structure, the first outer cladding layer having a third refractive index, n_outer—

₁, wherein the materials of the cladding layer and the buffer layer are selected such that n_inter>

n<sub>outer—

1</sub>, so that a field profile of an optical signal propagating through the core layers is asymmetric with respect to the core layers, and the photonic band region is effective to perturb an evanescent field of the optical signal.

44. A method of manufacturing double core planar waveguide structures;

comprising the steps of;

depositing a buffer layer;

depositing a first core layer over said buffer layer;

depositing an inter-core cladding layer;

defining a sub-region pattern;

etching inter-core sub-regions at least partially through the inter-core cladding layer in accordance with the sub-region pattern;

depositing a second core layer over the inter-core cladding layer; and

depositing a capping layer over the second core layer.

45. A method as claimed in claim 44, further comprising the step of:

filling the inter-core sub-regions with a third material after etching and before depositing the second core layer.

46. A method as claimed in claim 45, further comprising the step of:

removing any excess third material after filling the inter-core sub-regions.

47. A method as claimed in claim 45, further comprising the step of:

depositing a thin layer of the inter-core cladding material after filling the inter-core sub-regions and before depositing the second core layer.

48. A method as claimed in claim 44, further comprising the step of:

defining a rib pattern; and

etching a rib structure through the second core layer.

49. A method as claimed in claim 48, further comprising the step of:

etching the rib structure through the inter-core cladding layer and the first core layer.

50. A method as claimed in claim 48, wherein the rib pattern is tapered.

51. A method of manufacturing double core planar waveguide structures having a first core layer, a second core layer and an inter-core cladding layer, the inter-core cladding layer comprising a first region having a first refractive index n_inter, the method comprising:

forming an array of sub-regions having a second refractive index n_sub within the inter-core cladding layer, the sub-regions not extending into the core layers, the array of sub-regions giving rise to a photonic band structure region, which is effective to perturb an evanescent field of an optical signal propagating through the core layer.

52. A method as claimed in claim 51, wherein the step of forming the array of sub-regions results in a waveguide structure having an effective mode index contrast, which acts upon the optical signal as the signal passes through the photonic band structure region, that is greater than 0.1 percent.

53. A method as claimed in claim 51, wherein the step of forming the array of sub-regions includes etching the sub-regions.

54. A method as claimed in claim 53, wherein the step of forming the array of sub-regions further includes allowing air to fill the etched sub-regions.

55. A method as claimed in claim 53, wherein the step of forming the array of sub-regions further includes filling the etched regions with a filler material that has a higher refractive index than air.

56. A method as claimed in claim 55, wherein the filler material is silicon.

57. A method as claimed in claim 51, wherein the array of sub-regions is a one dimensional array.

58. A method as claimed in claim 51, wherein the array of sub-regions is a two dimensional array.

59. A method as claimed in claim 51, further comprising:

providing a first outer cladding layer, the first outer cladding layer comprising a first outer cladding region having a third refractive index n<sub>outer—

1</sub>.

60. A method as claimed in claim 59, wherein the method further comprises:

forming an array of first outer cladding sub-regions having a fourth refractive index, n<sub>out—

sub—

1</sub>, in the first outer cladding layer, the first outer cladding sub-regions not extending into the core layers, the array of first outer cladding sub-regions giving rise to a first outer cladding photonic band structure region, which is effective to perturb an evanescent field of an optical signal propagating through the core layer.

61. A method as claimed in claim 59, wherein the step of forming the array of first outer cladding sub-regions results in a waveguide structure having an effective mode index contrast acting upon the optical signal as the signal passes through the photonic band structure region that is greater than 0.1 percent.

62. A method as claimed in claim 60, wherein the step of forming the array of first outer cladding sub-regions includes etching the first outer cladding sub-regions.

63. A method as claimed in claim 62, wherein the step of forming the array of first outer cladding sub-regions further includes allowing air to fill the etched buffer sub-regions.

64. A method as claimed in claim 62, wherein the step of forming the array of first outer cladding sub-regions further includes filling the etched first outer cladding sub-regions with a filler material that has a higher refractive index than air.

65. A method as claimed in claim 64, wherein the filler material is silicon.

66. A method as claimed in claim 61, wherein the array of first outer cladding sub-regions is a one dimensional array.

67. A method as claimed in claim 61, wherein the array of first outer cladding sub-regions is a two dimensional array.

68. A method as claimed in claim 60, wherein the cladding layer is formed of a first material and the first outer cladding layer is formed of a second material, and wherein the first material has a higher refractive index than the second material.

69. A method of manufacturing annular waveguide structures comprising:

forming an annular core layer;

forming an inner cladding layer, wherein the inner cladding layer is substantially surrounded by the annular core layer and wherein the inner cladding layer comprises a first region having a first refractive index, n_inner; and

in the inner cladding layer, forming a one-dimensional array of sub-regions having a second refractive index, n_sub, which do not extend into the annular core layer, the array of sub-regions giving rise to a photonic band structure region, which is effective to perturb an evanescent field of an optical signal propagating through the core layer.

70. A method as claimed in claim 69, wherein the annular core layer is formed by coating an outer surface of a tube of inner cladding material with a core layer material.

71. A method as claimed in claim 70, wherein the formation of the inner cladding layer includes:

inserting a solid rod of inner cladding material inside the coated tube;

heating the tube and the coated rod until the tube and rod fuse; and

then pulling the fused structure longitudinally.

72. A method as claimed in claim 70, wherein the formation of the inner cladding layer includes:

inserting a number of glass tubes of inner cladding material inside the coated tube;

heating the tube and the coated rod until the tube and rod fuse to form a fused structure having a corresponding number of longitudinal cavities; and

then pulling the fused structure longitudinally.

73. A method as claimed in claim 72, wherein the average first refractive index, n_inner, is substantially 1.

74. A method as claimed in claim 69, further including:

providing an outer capping layer that substantially surrounds the annular core layer.

75. A method of guiding an optical signal comprising the step of passing an optical signal through a waveguiding region of a planar optical waveguide structure comprising a first core layer, a second core layer and an inter-core cladding layer;

wherein the inter-core cladding layer comprises a first region having a first refractive index n_inter, and an array of sub-regions having a second refractive index n_sub, the sub-regions not extending into the core layers, and

wherein the array of sub-regions gives rise to a photonic band structure region, which is effective to perturb an evanescent field of the optical signal propagating through the core layers.