Optical waveguide structure

• US 20060029348A1
• Filed: 03/28/2005
• Published: 02/09/2006
• Est. Priority Date: 02/19/2002
• Status: Active Grant

• Current Assignee: Richard Nagler
• Original Assignee: Optinetrics, Inc.
• Inventors: Tyan, Rongchung, Kempen, Lothar U., Mendoza, Edgar A.
• Granted Patent: US 7,391,948 B2
• Time in Patent Office: Days
• US Class Current: 385/129
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/2821 using lateral coupling between contiguous fibres to split or combine optical signals

Abstract

Waveguide structures in which light confinement strength varies along the direction of light propagation are described. The waveguides include a core adapted to propagate light along a path defined by the core and a cladding material that at least partially surrounds the core. The core and the cladding material each have a refractive index profile in the direction of light propagation. One or more of the profiles or lateral core dimensions are varied along the direction of light propagation, thereby causing the degree of light confinement to vary in the direction of light propagation. With such structures it is possible to tailor the velocity of the light propagating through the core and the confinement of the light to the core for any given core cross section. The structures may be used, for example, in mode-matching an input or output of a waveguide and in fabricating compact directional couplers.

Claims

1. A waveguide structure comprising:

a. a core having a lateral dimension and a vertical dimension and adapted to propagate light along a path defined by the core; and

b. a cladding material at least partially surrounding the core, the core and the cladding material each having a refractive index profile in a direction light propagates through the core, wherein at least one of (1) the lateral dimension of the core or (2) the refractive index profile of the core vary along a predefined portion of the core, and wherein the refractive index profile of the cladding includes a gradient along the predefined portion.

2. A waveguide structure according to claim 1, wherein the refractive index profile of the core and the refractive index profile of the cladding material are defined to only permit propagation of single-mode light in at least one transverse direction to the core.

3. A waveguide structure according to claim 1, wherein the refractive index profile of the cladding material comprises a refractive index profile for cladding material horizontally adjacent to the core.

4. A waveguide structure according to claim 3, wherein the core comprises a channel waveguide coupled to a taper that laterally flares out from the channel waveguide.

5. A waveguide structure according to claim 4, wherein the refractive index profile of the core in the region of the channel waveguide and the taper is defined by a first refractive index value, n₁.

6. A waveguide structure according to claim 5, wherein the refractive index profile of the cladding material horizontally adjacent to the core is graded from a second refractive index value, n₂, at the widest point of the taper to a third refractive index value, n₃, where the taper is coupled to the channel waveguide, where n₁>

n₂>

n₃.

7. A waveguide structure according to claim 6, wherein the difference between n₁ and n₃ is greater than 0.3% of n₃ and the difference between n₁ and n₂ is set in the range of 0.2% to 0.3% of n₂.

8. A waveguide structure according to claim 7, wherein the difference between n₁ and n₃ is greater than or equal to 0.8% of n₃.

9. A waveguide structure according to claim 1, wherein the refractive index profile of the cladding material comprises a refractive index profile for cladding material vertically adjacent to the core.

10. A waveguide structure according to claim 9, wherein the core comprises a channel waveguide coupled to a taper that laterally flares out from the channel waveguide.

11. A waveguide structure according to claim 10, wherein the refractive index profile of the core in the region of the channel waveguide is defined by a first refractive index value, n₁, and wherein the refractive index profile of the core is graded from a second index value, n₂, at the widest point of the taper to n₁ where the taper is coupled to the channel waveguide, where n₁>

n₂.

12. A waveguide structure according to claim 11, wherein the refractive index profile of the cladding material vertically adjacent to the core is graded from a third refractive index value, n₃, at the widest point of the taper to a fourth refractive index value, n₄, where the taper is coupled to the channel waveguide, where n₁>

n₄, n₂>

n₃, and n₄>

n₃.

13. A waveguide structure according to claim 12, wherein a constant Δ

n exists between the refractive index profile of the cladding material vertically adjacent to the core and the refractive index profile of the core.

14. A waveguide structure according to claim 11, wherein a constant Δ

n value in the range of 0.2% and 0.3% exists between the refractive index profile of the cladding material vertically adjacent to the core and the refractive index profile of the core.

15. A waveguide structure according to claim 11, wherein the refractive index profile of the cladding material vertically adjacent to the core is defined by a third refractive index value, n₃, in a first and second region vertically above and below the channel waveguide, respectively, and wherein the refractive index profile of the cladding material vertically adjacent to the core is graded in a third and forth region vertically above and below the taper, respectively, from a fourth refractive index value, n₄, at the widest point of the taper to the third refractive index value, n₃, where the taper is coupled to the channel waveguide, where n₁>

n₂>

n₄>

n₃.

16. A waveguide structure according to claim 15, wherein the cladding material comprises a second refractive index profile in the direction light propagates through the core, and the second refractive index profile comprises a refractive index profile for cladding material horizontally adjacent to the core, and wherein the second refractive index profile is defined by the third refractive index value, n₃.

17. A waveguide structure according to claim 15, wherein the third and fourth regions comprise second and third tapers having lateral dimensions that are substantially the same as the lateral dimensions of the taper in the core.

18. A waveguide structure according to claim 15, wherein the vertically adjacent cladding material comprises regions laterally adjacent to the third and fourth regions and the refractive index of these laterally adjacent regions is set equal to the third refractive index value, n₃.

19. A waveguide structure according to claim 15, wherein the difference between n₁ and n₃ is greater than or equal to 0.8% of n₃ and the difference between n₂ and n₃ is greater than or equal to 0.2% of n₃ and less than or equal to 0.4% of n₃.

20. A waveguide structure according to claim 9, wherein the core comprises a channel waveguide coupled to a taper that laterally tapers inwardly from the channel waveguide.

21. A waveguide structure according to claim 20, wherein the refractive index profile of the core in the region of the channel waveguide and the taper is defined by a first refractive index value, n₁.

22. A waveguide structure according to claim 21, wherein the refractive index profile of the cladding material vertically adjacent to the core is graded from a second refractive index value, n₂, at the narrowest point of the taper to a third refractive index value, n₃, where the taper is coupled to the channel waveguide, where n₁>

n₂>

n₃.

23. A waveguide structure according to claim 22, wherein the difference between n₁ and n₃ is greater than or equal to 0.8% of n₃.

24. A waveguide structure according to claim 9, wherein the gradient included in the refractive index profile of the cladding material vertically adjacent to the core is graded to cause an evanescent field of light propagating through the core to expand or contract with respect to the core in a vertically transverse direction to the core along the predefined portion of the core.

25. A waveguide structure comprising:

a. a core a adapted to propagate light along a path defined by the core, the core having a lateral dimension, a vertical dimension, and a first refractive index profile in a direction light propagates through the core; and

b. a cladding material at least partially surrounding the core, the cladding material having a second and a third refractive index profile in the direction light propagates through the core, the second refractive index profile defining a refractive index profile of cladding material horizontally adjacent to the core, and the third refractive index profile defining a refractive index profile of cladding material vertically adjacent to the core, wherein at least one core parameter selected from the group consisting of (1) the lateral dimension of the core and (2) the refractive index profile of the core vary along a predefined portion of the core, and wherein at least one of the second and third refractive index profiles includes a gradient along the predefined portion.

26. A waveguide structure according to claim 25, wherein the first, second and third refractive index profiles are defined to only permit propagation of single-mode light through the core.

27. A waveguide structure according to claim 25, wherein the core comprises a channel waveguide coupled to a taper that laterally flares out from the channel waveguide.

28. A waveguide structure according to claim 27, wherein the first refractive index profile of the core in the region of the channel waveguide and the taper is characterized by a first refractive index value, n₁.

29. A waveguide structure according to claim 28, wherein the second refractive index profile is graded from a second refractive index value, n₂, at the widest point of the taper to a third refractive index value, n₃, where the taper is coupled to the channel waveguide, where n₁>

n₂>

n₃, and wherein the third refractive index profile is characterized by a constant refractive index value equal to n₂.

30. A waveguide structure according to claim 29, wherein the difference between n₁ and n₃ is greater than 0.3% of n₃ and the difference between n₁ and n₂ is set in the range of 0.2% to 0.3% of n₂.

31. A waveguide structure according to claim 30, wherein the difference between n₁ and n₃ is greater than or equal to 0.8% of n₃.

32. A waveguide structure according to claim 27, wherein the first refractive index profile of the core in the region of the channel waveguide is defined by a first refractive index value, n₁, and wherein the first refractive index profile of the core is graded from a second index value, n₂, at the widest point of the taper to n₁ where the taper is coupled to the channel waveguide, where n₁>

n₂.

33. A waveguide structure according to claim 32, wherein the third refractive index profile is graded from a third refractive index value, n₃, at the widest point of the taper to a fourth refractive index value, n₄, where the taper is coupled to the channel waveguide, where n₁>

n₄, n₂>

n₃, and n₄>

n₃, and wherein the second refractive index profile is characterized by a constant refractive index value equal to n₃.

34. A waveguide structure according to claim 33, wherein the third refractive index profile of the cladding material is defined to provide a constant Δ

n with respect to the core.

35. A waveguide structure according to claim 33, wherein the third refractive index profile of the cladding material is defined to provide a constant Δ

n value in the range of 0.2% and 0.3% with respect to the core.

36. A waveguide structure according to claim 33, wherein the difference between n₁ and n₃ is greater than or equal to 0.8% of n₃ and the difference between n₂ and n₃ is set in the range of 0.2% to 0.3% of n₃.

37. A waveguide structure according to claim 25, wherein the core comprises a channel waveguide coupled to a taper that laterally tapers inwardly from the channel waveguide.

38. A waveguide structure according to claim 37, wherein the refractive index profile of the core in the region of the channel waveguide and the taper is defined by a first refractive index value, n₁.

39. A waveguide structure according to claim 38, wherein the third refractive index profile is graded from a second refractive index value, n₂, at the narrowest point of the taper to a third refractive index value, n₃, where the taper is coupled to the channel waveguide, where n₁>

n₂>

n₃, and wherein the second refractive index profile comprises a constant refractive index value equal to n₃.

40. A waveguide structure according to claim 39, wherein the difference between n₁ and n₃ is greater than or equal to 0.8% of n₃.

41. A waveguide structure according to claim 25, wherein the third refractive index profile includes a gradient along the predefined portion of the core and the gradient is graded to cause an evanescent field of light propagating through the core to expand or contract with respect to the core in a vertically transverse direction to the core.

42. A waveguide structure comprising:

a. a core a adapted to propagate light along a path defined by the core, the core having a lateral dimension, a vertical dimension, and a first refractive index profile in a direction light propagates through the core; and

b. a cladding material at least partially surrounding the core, the cladding material having a second and a third refractive index profile in the direction light propagates through the core, the second refractive index profile defining a refractive index profile of cladding material horizontally adjacent to the core, and the third refractive index profile defining a refractive index profile of cladding material vertically adjacent to the core, wherein at least one core parameter selected from the group consisting of (1) the lateral dimension of the core and (2) the refractive index profile of the core vary along a predefined portion of the core, and wherein at least one of the second and third refractive index profiles includes a gradient along the predefined portion, and the refractive index of at least one of the horizontally adjacent cladding material and vertically adjacent cladding material varies in a direction lateral to the core along the predefined portion of the core.

43. A waveguide structure comprising:

a. a first core adapted to propagate light along a first path, the first core having a first refractive index profile in a direction light propagates through the first core; and

b. a cladding material at least partially surrounding the first core, the cladding material having a second refractive index profile adjacent the first core and in a direction light propagates through the first core, wherein the first refractive index profile, the second refractive index profile, or both include a gradient along a predefined portion of the first core causing an evanescent field of light propagating through the first core to expand or contract with respect to the first core as the light propagates through the predefined portion of the first core.

44. A waveguide structure according to claim 43, wherein the first core comprises a channel waveguide having a uniform vertical dimension.

45. A waveguide structure according to claim 44, wherein the second refractive index profile is graded along the predefined portion of the first core in a manner which causes reduced light confinement in the core along the predefined portion.

46. A waveguide structure according to claim 44, wherein the first refractive index profile is graded along the predefined portion of the first core in a manner which causes reduced light confinement in the core along the predefined portion.

47. A waveguide structure according to claim 44, wherein the predefined portion of the first core comprises an input for the waveguide and the first refractive index profile, the second refractive index profile, or both are graded along the predefined portion of the first core to cause the evanescent field of light propagating through the core to contract with respect to the first core as the light propagates through the predefined portion of the first core.

48. A waveguide structure according to claim 44, wherein the predefined portion comprises an output for the waveguide and the first refractive index profile, the second refractive index profile, or both are graded along the predefined portion of the first core to cause the evanescent field of light propagating through the core to expand with respect to the first core as the light propagates through the predefined portion of the first core.

49. A waveguide structure according to claim 43, wherein the Δ

n between the first refractive index profile and the second refractive index profile is reduced in the predefined portion of the first core.

50. A waveguide structure according to claim 49, further comprising a second core spaced apart from the first core and adapted to propagate light along a second path, the second core being at least partially surrounded by the cladding material and having a third refractive index profile, the second path including a region that is disposed sufficiently close to the predefined portion of the first core that light propagating through the predefined portion of the first core is coupled to the second core.

51. A waveguide structure according to claim 50, wherein less than −

10 dB/cm of light is coupled from the first core to the second core outside of the predefined portion.

52. A waveguide structure according to claim 51, wherein the first and second paths are parallel to one another.

53. A waveguide structure comprising:

a. a first core adapted to propagate light along a first path defined by the first core, the first core having a first refractive index profile in a direction light propagates through the first core; and

b. a cladding material surrounding the core, the cladding material having a second and a third refractive index profile in the direction light propagates through the first core, the second refractive index profile defining a refractive index profile of cladding material horizontally adjacent to the first core, and the third refractive index profile defining a refractive index profile of cladding material vertically adjacent to the first core, wherein at least one of the first, second, or third refractive index profiles vary along a predefined portion of the first core so as to cause an enlargement or contraction of the evanescent field of light propagating through the first core with respect to the first core as the light propagates through the predefined portion of the first core.