Alignment of optical waveguides

• US 20030194186A1
• Filed: 04/16/2002
• Published: 10/16/2003
• Est. Priority Date: 04/16/2002
• Status: Active Grant

• Current Assignee: National Research Council Canada
• Original Assignee: National Research Council Canada
• Inventors: Taylor, Rod, Hnatovsky, Cyril
• Granted Patent: US 6,859,589 B2
• Time in Patent Office: Days
• US Class Current: 385/52
• CPC Class Codes: G02B 6/255 Splicing of light guides, e.g. by fusion or bonding
• CPC Class Codes: G02B 6/2551 using thermal methods, e.g. fusion welding by arc discharge, laser beam, plasma torch
• CPC Class Codes: G02B 6/262 Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
• CPC Class Codes: G02B 6/3803 Adjustment or alignment devices for alignment prior to splicing

Abstract

In order to make alignable optical waveguides, an alignment structure is formed on at least one opposable end of the waveguides by selective chemical etching of different portions of the waveguides. The waveguides can then be brought into alignment with the alignment structure. Preferably, a pair of complementary alignment structures are formed on opposed ends of adjoining waveguides.

Claims

1. A method of aligning optical waveguides having portions with different etch characteristics, comprising:

forming an alignment structure on at least one opposable end of said waveguides by selective chemical etching of said portions relative to each other; and

bringing said waveguides into alignment with the aid of said alignment structure.

2. A method as claimed in claim 1, wherein complementary alignment structures are formed on said opposable ends of said waveguides so as to permit docking thereof.

3. A method as claimed in claim 2, wherein said waveguides comprise a core surrounded by a cladding layer, and said selective chemical etching is carried out with chemical etchants that preferentially etch said core or said cladding layer.

4. A method as claimed in claim 3, wherein said selective chemical etching is carried out on one of said opposable ends with a first chemical etchant that preferentially etches said cladding layer.

5. A method as claimed in claim 4, wherein said first etchant contains a buffered oxide etchant (BOE).

6. A method as claimed in claim 4, wherein said cladding layer is preferentially etched to form a generally conical structure providing one of said complementary alignment structures.

7. A method as claimed in claim 3, wherein said selective chemical etching is carried out on the other of said opposable ends with a second etchant that preferentially etches said core.

8. A method as claimed in claim 7, wherein said second etchant contains hydrofluoric acid solution.

9. A method as claimed in claim 7, wherein the core is preferentially etched to provide a recess forming the other of said complementary alignment structures.

10. A method as claimed in claim 2, wherein regions of said opposable ends are doped, and said doped regions are selectively etched to provide said complementary alignment structures.

11. A method as claimed in claim 2, wherein regions of said opposable ends are modified so that they can be preferentially etched, and said modified regions are preferentially etched to provide said complementary alignment structures.

12. A method as claimed in claim 11, wherein two or more said regions are modified on each of said opposable ends so that they can be preferentially etched to form a corresponding number of said complementary alignment structures.

13. A method as claimed in claim 12, wherein said waveguides comprise a core surrounded by a cladding layer, and said selected regions are formed in the cladding layer.

14. A method as claimed in claim 13, wherein said complementary alignment structures comprise protrusions and complementary recesses.

15. A method as claimed in claim 2, wherein one or more of the waveguides is a fiber and wherein the diameter of one of said fibers adjacent said opposable end thereof is reduced by etching to increase its flexibility and permit the waveguides to snap together in a coaxial fashion during docking of said complementary structures.

16. A method as claimed in claim 15, wherein said diameter is reduced by a factor of about 3.

17. A method as claimed in claim 14, wherein the diameter of the other of said waveguides adjacent the opposable end thereof is reduced by etching by an amount less than said one waveguide.

18. A method as claimed in claim 17, wherein the diameter of said other waveguide is reduced by about 20%.

19. A method of aligning optical waveguides having portions with different etch characteristics, comprising:

providing an alignment structure on at least one opposable end of said waveguides by selective chemical etching of said portions relative to each other;

gradually bringing said opposable ends together;

monitoring the relative position of said alignment structure as a gap between said opposable ends closes; and

effecting relative positioning of said waveguides to bring said waveguides into alignment.

20. A method as claimed in claim 19, wherein said monitoring is based upon the size of a gap between said opposable ends and is carried out with the aid of a feedback system that generates an output signal controlling the relative position of said waveguides.

21. A method as claimed in claim 20, wherein said feedback system comprises a light source which transmits a light beam at one or more wavelengths that can pass between but not through said opposable ends, and a detector monitoring the amount of light transmitted through a gap between said opposable ends as said opposable ends come together.

22. A method as claimed in claim 20, wherein said waveguides are optical fibers and said gap is monitored by observing the movement of a mark located on the side of one of the fibers containing said alignment structure and adjacent the end thereof.

23. A method as claimed in claim 22, wherein the location of said mark relative to a reference point in a microscope is monitored to generate a feedback signal for said feedback system.

24. A method as claimed in claim 20, wherein said feedback system comprises a vision system that monitors the relative position of said opposable ends.

25. A method as claimed in claim 24, wherein one of said opposable ends carries a first said alignment structure, a virtual image of said first alignment structure is formed in the other of said opposable ends, said vision system is aimed at said virtual image, and said opposable ends are brought into alignment by aligning said virtual image with a target on said other of said opposable ends.

26. A method as claimed in claim 25, wherein said vision system is also aimed at a virtual image of the perimeter of said opposable end carrying said first alignment structure and a real image of said perimeter so as to permit monitoring of the gap between said images as said opposable ends are brought together.

27. A method as claimed in claim 25, wherein said target is a second alignment structure.

28. A method as claimed in claim 27, wherein said second alignment structure comprises a recess for accommodating said first alignment structure.

29. A method as claimed in claim 25, wherein said target defines the core/cladding boundary on said other of said opposable ends.

30. A method as claimed in claim 25, wherein said target is an illuminated region on said other of said opposable ends.

31. A method as claimed in claim 25, wherein said vision system has an optical axis lying at an oblique angle to said opposable ends so that said virtual image and said target remain in view of said vision system as said opposable ends are brought together.

32. A method as claimed in claim 25, wherein said feedback system generates a control signal that iteratively alters the relative position of said opposable ends until said waveguides come into alignment.

33. A method as claimed in claim 19, wherein complementary alignment structures are formed on said respective opposable ends.

34. A method as claimed in claim 19, wherein said optical waveguides have a core surrounded by a cladding layer, a generally conical alignment structure is formed on the core of one said opposable end by selective chemical etching, the core of the other opposable end is illuminated by light passing therethrough, and said conical structure is aligned with said core of the other opposable end with the aid of said illuminated core.

35. A method as claimed in claim 19, wherein said optical waveguides have a core surrounded by a cladding layer, a conical alignment structure is formed on the core of one said opposable end by selective chemical etching, the core of the other opposable end has a shallow recess formed therein, said shallow recess is illuminated to identify the core/cladding boundary, and said conical structure is aligned with said core of the other opposable end with the aid of said illuminated shallow recess.

36. A method as claimed in claim 35, wherein said shallow recess has a depth in the order of λ

/4, where λ

is the wavelength of light used to reflect off and visualize the shallow recess.

37. A method as claimed in claim 34, wherein the core of the other opposable end forms part of a microfabricated array of waveguides.

38. A method as claimed in claim 36, wherein the core of the other opposable end forms part of a microfabricated array of waveguides.

40. A method as claimed in claim 33, wherein at least one of said waveguides is a fiber and has a sufficiently low effective spring constant to permit said waveguides to flexibly snap together in a coaxial fashion as they come into contact.

41. A method as claimed in claim 40, wherein said waveguides are mounted in respective holders leaving end portions thereof free, and said effective spring constant can be varied by changing the distance between the tip of said fiber and the position where the fiber is first clamped inside its respective holder and/or by changing the diameter of the fiber.

42. A method as claimed in claim 41, wherein said distance and/or said diameter can be varied to optimize the fiber flexibility to provide good docking.