An optical coupler and method of making same is described. The coupling ratio of the coupler is polarization-insensitive. The optical coupler described herein is made from single-mode optical fibers. Each optical fiber has a length of nearly exposed core which is fused to the exposed core of the other optical fiber while the fibers are maintained in parallel juxtaposition with one another without twisting. By creating a fused core coupler from single-mode optical fibers in which the cores are in parallel juxtaposition with one another, the coupling ratio of the subject invention does not change with changes in polarization of light passing through each single-mode fiber and, thus, is polarization insensitive.
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7. A method of making a polarization-insensitive optical coupler comprising the steps of:
(a) etching first and second longitudinal segments of first and second single-mode optical fibers so that each fiber has an outer cladding have having a low index of refraction relative to the index of refraction of a nearly exposed core of each of the first and second single-mode optical fibers; (b) maintaining the first and second single-mode optical fibers in parallel juxtaposition with one another along a portion of each of the first and second longitudinal segments while placing the first and second longitudinal segments under axial tension; (c) fusing the parallel juxtaposition portions of the first and second longitudinal segments together while the first and second longitudinal segments are maintained in parallel juxtaposition and remain under axial tension, so that a coupling region is formed.
13. A method of making a polarization-insensitive optical coupler comprising the steps of:
(a) etching first and second longitudinal segments of first and second single-mode optical fibers so that each fiber has an outer cladding having a low index of refraction relative to the index of refraction of a nearly exposed core of each of the first and second single-mode optical fibers; (b) maintaining the first and second single-mode optical fibers in parallel juxtaposition with one another along a portion of each of the first and second longitudinal segments, said maintaining step including the substeps of: (b1) wrapping portions of the first and second longitudinal segments with a material which will not substantially deform the nearly exposed cores of the first and second single-mode optical fibers; (b2) bonding the nearly exposed cores of the first and second single-mode optical fibers together while the nearly exposed cores of the first and second single-mode optical fibers are wrapped; and (b3) unwrapping the nearly exposed cores of the first and second single-mode optical fibers; and (c) fusing the parallel juxtaposition portions of the first and second longitudinal segments together to form a coupling region.
1. A method of making a polarization-insensitive optical coupler comprising the steps of:
(a) etching first and second longitudinal segments of first and second single-mode optical fibers so that each fiber has an outer cladding having a low index of refraction relative to the index of refraction of a nearly exposed core of each of the first and second single-mode optical fibers; (b) maintaining the first and second single-mode optical fibers in parallel juxtaposition with one another along a portion of each of the first and second longitudinal segment segments, said maintaining step comprising the substeps of: (b1) wrapping portions of the first and second longitudinal segments with a material which will not substantially deform the nearly exposed cores of the first and second single-mode optical fibers; (b2) gluing the nearly exposed cores of the first and second single-mode optical fibers together with glue while the nearly exposed cores are wrapped; (b3) curing the glue; and (b4) unwrapping the nearly exposed cores; (c) fusing together the portions of the first and second longitudinal segments maintained in parallel juxtaposition to form a coupling region; and (d) rigidly encapsulating the nearly exposed cores of the first and second single-mode optical fibers while maintaining the parallel juxtaposition of the first and second longitudinal segments.
2. A method of making a polarization-insensitive optical couopler as recited in
3. A method of making a polarization-insensitive optical coupler as recited in
4. A method of making a polarization-insensitive optical coupler as recited in
5. A method of making a polarization-insensitive optical coupler as recited in
6. A method of making a polarization-insensitive optical coupler as recited in
(d1) placing a tube having ends and having a length substantially the same as the first and second longitudinal segments over the coupling region; (d2) gluing the ends of the tube to the first and second single-mode optical fibers with glue to suspend the fibers within the tube; and (d3) curing the glue.
8. A method of making a polarization-insensitive optical coupler as recited in
9. A method of making a polarization-insensitive optical coupler as recited in
10. A method of making a polarization-insensitive optical coupler as recited in
(b1) wrapping portions of the first and second longitudinal segments with a material which will not substantially deform the nearly exposed cores of the first and second single-mode optical fibers; (b2) bonding the nearly exposed cores of the first and second single-mode optical fibers together while the nearly exposed cores of the first and second single-mode optical fibers are wrapped; and (b3) unwrapping the nearly exposed cores of the first and second single-mode optical fibers.
11. A method of making a polarization-insenstive polarization-insensitive optical coupler as recited in
gluing the nearly exposed cores of the first and second single-mode optical fibers together with glue while the nearly exposed cores are wrapped; and curing the glue.
12. A method of making a polarization-insensitive optical coupler as recited in
14. A method of making a polarization-insensitive optical coupler as recited in
15. A method of making a polarization-insensitive optical coupler as recited in
gluing the nearly exposed cores of the first and second single-mode optical fibers together with glue while the nearly exposed cores are wrapped; and curing the glue.
16. A method of making a polarization-insensitive optical coupler as recited in
17. A method of making a polarization-insenstive polarization-insensitive optical coupler as recited in
18. A method of making a polarization-insensitive optical coupler as recited in
said maintaining step (b) further comprises the substep of placing the first and second longitudinal segments under axial tenson; and said fusing step (c) comprises fusing the parallel juxtaposition portions of the first and second longitudinal segments together while the first and second longitudinal segments are maintained in parallel juxtaposition and remain under axial tension.
19. A method of making a polarization-insensitive optical coupler as claimed in
placing a tube having ends and having a length substantially the same as the first and second longitudinal segments over the coupling region; gluing the ends of the tube to the first and second single-mode optical fibers with glue to suspend the fibers within the tube; and
curing the glue. 21. A polarization-insensitive optical coupler prepared by a method comprising the steps of: (a) etching first and second longitudinal segments of first and second single-mode optical fibers so that each fiber has an outer cladding having a low index of refraction relative to the index of refraction of a nearly exposed core of each of the first and second single-mode optical fibers; (b) maintaining the first and second single-mode optical fibers in parallel juxtaposition with one another along a portion of each of the first and second longitudinal segments, said maintaining step comprising the substeps of: (b1) wrapping portions of the first and second longitudinal segments with a material which will not substantially deform the nearly exposed cores of the first and second single-mode optical fibers; (b2) gluing the nearly exposed cores of the first and second single-mode optical fibers together with glue while the nearly exposed cores are wrapped; (b3) curing the glue; and (b4) unwrapping the nearly exposed cores; (c) fusing together the portions of the first and second longitudinal segments maintained in parallel juxtaposition to form a coupling region; and (d) rigidly encapsulating the nearly exposed cores of the first and second single-mode optical fibers while maintaining the parallel juxtaposition of the first and second longitudinal segments, said step (d) including the substeps of: (d1) placing a tube having ends and having a length substantially the same as the first and second longitudinal segments over the coupling region; (d2) gluing the ends of the tube to the first and second single-mode optical fibers with glue to suspend the fibers within the tube; and (d3) curing the glue. 22. A polarization-insensitive optical coupler as recited in claim 21, wherein said step (a) comprises etching the first and second longitudinal segments along a length in the range of 0.5 to 2 cm. 23. A polarization-insensitive optical coupler as recited in claim 21, wherein said step (a) includes removing an outer jacket of each of the first and second single-mode optical fibers along the length of the nearly exposed cores of the first and second single-mode optical fibers. 24. A polarization-insensitive optical coupler as recited in claim 21, wherein said step (a) includes rinsing the first and second longitudinal segments of the first and second single-mode optical fibers in hydrofluoric acid to remove any room temperature vulcanizing rubber which may be surrounding the cladding of the first and second single-mode optical fibers. 25. A polarization-insensitive optical coupler as recited in claim 21, wherein said step (b) includes aligning the first and second single-mode optical fibers in a holder having alignment grooves prior to said substep (b1). 26. A polarization-insensitive optical coupler prepared by a method comprising the steps of: (a) etching first and second longitudinal segments of first and second single-mode optical fibers so that each fiber has an outer cladding having a low index of refraction relative to the index of refraction of a nearly exposed core of each of the first and second single-mode optical fibers; (b) maintaining the first and second single-mode optical fibers in parallel juxtaposition with one another along a portion of each of the first and second longitudinal segments while placing the first and second longitudinal segments under axial tension; (c) fusing the parallel juxtaposition portions of the first and second longitudinal segments together while the first and second longitudinal segments are maintained in parallel juxtaposition and remain under axial tension, so that a coupling region is formed; and (d) rigidly encapsulating the nearly exposed cores of the first and second single-mode optical fibers in a quartz tube while maintaining the parallel-juxtaposition of the first and second longitudinal segments. 27. A polarization-insensitive optical coupler as recited in claim 26, wherein said step (b) comprises the substeps of: (b1) wrapping portions of the first and second longitudinal segments with a material which will not substantially deform the nearly exposed cores of the first and second single-mode optical fibers; (b2) bonding the nearly exposed cores of the first and second single-mode optical fibers together while the nearly exposed cores of the first and second single-mode optical fibers are wrapped; and (b3) unwrapping the nearly exposed cores of the first and second single-mode optical fibers. 28. A polarization-insensitive optical coupler as recited in claim 27, wherein said substep (b2) comprises: gluing the nearly exposed cores of the first and second single-mode optical fibers together with glue while the nearly exposed cores are wrapped; and curing the glue. 29. A polarization-insensitive optical coupler as recited in claim 27, wherein said substep (b1) comprises wrapping portions of the first and second longitudinal segments with a thin plastic sheet. 30. A polarization-insensitive optical coupler as recited in claim 26, wherein said step (b) comprises wrapping portions of the first and second longitudinal segments with a material which will not substantially deform the nearly exposed cores of the first and second single-mode optical fibers. 31. A polarization-insensitive optical coupler prepared by a method comprising the steps of: (a) etching first and second longitudinal segments of first and second single-mode optical fibers so that each fiber has an outer cladding having a low index of refraction relative to the index of refraction of a nearly exposed core of each of the first and second single-mode optical fibers; (b) maintaining the first and second single-mode optical fibers in parallel juxtaposition with one another along a portion of each of the first and second longitudinal segments, said maintaining step comprising the substeps of: (b1) wrapping portions of the first and second longitudinal segments with a material which will not substantially deform the nearly exposed cores of the first and second single-mode optical fibers; (b2) bonding the nearly exposed cores of the first and second single-mode optical fibers together while the nearly exposed cores of the first and second single-mode optical fibers are wrapped; and (b3) unwrapping the nearly exposed cores of the first and second single-mode optical fibers; (c) fusing the parallel juxtaposition portions of the first and second longitudinal segments together to form a coupling region; and (d) rigidly encapsulating the nearly exposed cores of the first and second single-mode optical fibers in a quartz tube while maintaining the parallel juxtaposition of the first and second longitudinal segments. 32. A polarization-insensitive optical coupler as recited in claim 31, wherein said substep (b1) comprises wrapping portions of the first and second longitudinal segments with a thin plastic sheet. 33. A polarization-insensitive optical coupler as recited in claim 32, wherein said substep (b2) comprises: gluing the nearly exposed cores of the first and second single-mode optical fibers together with glue while the nearly exposed cores are wrapped; and curing the glue. 34. A polarization-insensitive optical coupler as recited in claim 31, wherein: said maintaining step (b) further comprises the substep of placing the first and second longitudinal segments under axial tension; and said fusing step (c) comprises fusing the parallel juxtaposition portions of the first and second longitudinal segments together while the first and second longitudinal segments are maintained in parallel juxtaposition and remain under axial tension. 35. A polarization-insensitive optical coupler prepared by a method comprising the steps of: (a) etching first and second longitudinal segments of first and second single-mode optical fibers so that each fiber has an outer cladding having a low index of refraction relative to the index of refraction of a nearly exposed core of each of the first and second single-mode optical fibers; (b) maintaining the first and second single-mode optical fibers in parallel juxtaposition with one another along a portion of each of the first and second longitudinal segments while placing the first and second longitudinal segments under axial tension; (c) fusing the parallel juxtaposition portions of the first and second longitudinal segments together while the first and second longitudinal segments are maintained in parallel juxtaposition and remain under axial tension, so that a coupling region is formed; and (d) rigidly encapsulating the nearly exposed cores of the first and second single-mode optical fibers while maintaining the parallel juxtaposition of the first and second longitudinal segments, said step of rigidly encapsulating the nearly exposed cores including the substeps of: (d1) placing a tube having ends and having a length substantially the same as the first and second longitudinal segments over the coupling region; (d2) gluing the ends of the tube to the first and second single-mode optical fibers with glue to suspend the fibers within the tube; and (d3) curing the glue. |
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This is a continuation of co-pending application Ser. No. 498,436 filed on May 26, 1983, now abandoned.
A. Field of the Invention
The present invention relates generally to optical waveguide couplers and more specifically to optical couplers using single-mode optical fibers that are resistant to polarization changes.
B. Description of the Prior Art
Fiber optic couplers are commonly used to transfer light from one optical waveguide to another for a variety of functions. For example, fiber optic couplers are used in the communications field to rapidly convey largersilicone silicon) coating. The plastic jacket is cut away and any RTV is removed with a hydrofluoric acid rinse.
Referring now to FIG. 4, after the fibers have been prepared as discussed above, each fiber 12 and 14 is placed in respective groves 30-33 of clamping devices 36, 38. The fibers are then cleaned with a hydrofluoric acid/water/alcohol rinse according to techniques known to those skilled in the art. After each fiber has been inspected for cleanliness, etching of the fibers is initiated. It is the object of the etching portion of the procedure to remove the substrate 16 and 18 of each fiber 12 and 14 (FIG. 1) to expose core and cladding 20 and 22 along a coupling region 24 of each of the fibers so as to provide an appropriate index profile. An appropriate index profile is one in which the outer surface, or cladding, of each fiber has a lower index of refraction than the core of each fiber. Although a variety of etching techniques may be used, in view of the particular fiber used in the preferred embodiment, it is desirable to etch the subject fibers by a heated etching technique. In this technique, the fibers are placed in close proximity to an etching station which is heated by a thermoelectric module. A drop of etchant is placd on top of the etching station to etch a longitudinal portion of the fiber. After the fiber has been etched to the desired diameter, the fibers are then rinsed with water to prevent further etching. The very fragile etched longitudinal segments 20, 22 are then brought in parallel juxtaposition with one another by wrapping opposite ends of each exposed core length to one another with a thread or other wrapping material 42, 44. In the preferred embodiment, it has been found that a thin plastic sheet is desirable to prevent breakage of the fragile cores 20, 22. After the cores have been temporarily wrapped as discussed above to provide the desired parallel juxtaposition special relationship, a small drop of adhesive material is deposited on each end 46, 48 of the exposed core length adjacent to threads 42, 44. The glue is allowed to cure so that the cores 20, 22 remain in parallel juxtaposition with one another throughout coupling region 24 when threads 42 and 44 are removed from the exposed cores 20, 22.
The coupling region of the fibers 12, 14 are then heated. In the laboratory technique used in the preferred embodiment, a lighted torch is simply passed along the coupling region 24 while the longitudinal segments are in axial tension until the segments 20, 22 are fused together throughout the length of the coupling region. A quartz tube 26 is then measured and cut to the desired length to surround the exposed cores of the subject coupler. In one embodiment, a slot extending the length of the quartz tube 26 may be provided to allow insertion of the tube about fibers 12, 14. In another embodiment, the tube may be cut in half longitudinally to allow each half to be simply placed about the fibers. The ends of the fibers 12, 14 are then glued to the ends 81, 83 of the quartz tube to suspend the etched and fused segments of the fibers containing the coupling region 24 in the approximate center of the tube 26. The glued assembly is then allowed to cure as necessary. The quartz tube is then dipped in a material to provide an elastic covering over tube 26.
The invention described herein is insensitive to changes in polarization due to its unique design. In other single-mode, evanescent-wave couplers, birefringence resulting from twists, bends, stresses, or strains imposed on the fibers will cause changes in polarity of light transmitted through the fibers. It is common practice in coupler manufacture to twist a pair of fibers about one another in order to maintain contact during fusing. By eliminating the need to twist the fibers about one another and by making bends in the fiber as gradual as possible, the polarization dependence of the coupling ratio is eliminated.
Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration an example only, and is not to be taken by way of limitation; the spirit and scope of this invention being limited only by the terms of the appended claims.
Stowe, David W., Kopera, Paul M.
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