Connector employing mode field modification

• US 4,763,976 A
• Filed: 05/21/1987
• Issued: 08/16/1988
• Est. Priority Date: 05/21/1987
• Status: Expired due to Term

• Current Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Original Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Inventors: Truesdale, Carlton M., Nolan, Daniel A.
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): FONT, FRANK G
• Application Number:
  US07/052,281
• Time in Patent Office: 453 Days
• Field of Search: 350/96.15, 350/96.20, 350/96.21, 350/96.29, 350/96.30, 350/96.33
• US Class Current: 385/43
• 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 6/3855 characterised by the method of anchoring or fixing the fibre within the ferrule G02B6/3854 takes precedence
• CPC Class Codes: G02B 6/3859 Ferrules characterised by use of shape memory material [SMM], e.g. heat recoverable polymers, Ti-Ni compounds chemical aspects of SMM see the relevant places under C08 and C22; SMM used for shaping by moulding B29C61/00; SMM for electrical coupling H01R4/01, H01R4/72, H01R12/856, H02G15/1806
• CPC Class Codes: G02B 6/4202 for coupling an active element with fibres without intermediate optical elements, e.g. fibres with plane ends, fibres with shaped ends, bundles

Abstract

Disclosed is a mode field modifier for use with an optical fiber having a core and a cladding of outside diameter d. The modifier comprises a modifier core having a refractive index n₁. Surrounding the modifier core is first cladding layer having a refractive index n₂ that is less n₁. On the surface of the first cladding layer is a second cladding layer having a refractive index n₃ which is less than n₂. The modifier is tapered intermediate its ends whereby it has a large diameter end and a small diameter end. The diameters of at least the core and first cladding layer at the large diameter end are greater than the corresponding diameters at the small end. The diameter D₁ of the first cladding layer at the large diameter end is greater than d. An axially disposed hole in the large diameter end receives a fiber which is held in such alignment with the mode field modifier that it is in light coupling relationship with the modifier core. The mode field of a signal coupled from the fiber to the mode field modifier expands as it propagates though the tapered portion of the modifier to the small diameter end. An in-line coupler between two optical fibers is effected by connecting together in axial alignment two such mode field modifiers with their small diameter ends adjacent one another.

Claims

1. A mode field modifier for use with an optical fiber having a core and a cladding of outside diameter d, said modifier comprising

a modifier core having a refractive index n₁,

a first cladding layer surrounding said modifier core, said first cladding layer having a refractive index n₂ that is less than n₁,

a second cladding layer on the surface of said first cladding layer, the refractive index n₃ of said second cladding layer being less than n₂, said modifier being tapered intermediate its ends whereby it has a large diameter end and a small diameter end, the diameters of at least said core and said first cladding layer at said large diameter end are greater than the corresponding diameters at said small diameter end, whereby the mode field of an optical signal propagating in one end of said modifier is modified as said signal propagates through the tapered portion of said modifier, the diameter D₁ of said first cladding layer at said large diameter end being greater than d, and

means for positioning a fiber at said large diameter end in light coupling relationship with said modifier core, said means for positioning comprising a hole in said large diameter end, said hole being concentric with said modifier core.

2. A mode field modifier in accordance with claim 1 wherein said first cladding layer comprises inner and outer layers of glass, said inner layer being more soluble in a given solvent than said outer layer.

3. A mode field modifier in accordance with claim 2 wherein the refractive index of said outer layer is substantially the same as that of said inner layer.

4. A mode field modifier in accordance with claim 2 wherein the refractive index of said outer layer is less than that of said inner layer.

5. A device for connecting first and second single-mode optical fibers of diameter d, said device comprising

first and second mode field modifiers, each having a modifier core having a refractive index n₁, a first cladding layer surrounding said modifier core,

said first cladding layer having a refractive index n₂ that is less than n₁,

a second cladding layer on the surface of said first cladding layer, the refractive index n₃ of said second cladding layer being less than n₂, said modifier being tapered intermediate its ends whereby it has a large diameter end and a small diameter end, the diameters of at least said core and said first cladding layer at said large diameter end are greater than the corresponding diameters at said small diameter end, whereby the mode field of an optical signal propagating in one end of said modifier is modified as said signal propagates through the tapered portion of said modifier, the diameters of said core and first cladding layer at said small diameter end being sufficiently small that the field of a signal propagating in said large diameter end of said coupler toward the small diameter end thereof is no longer confined to said core and first cladding but it spreads and is effectively guided by the waveguide consisting of said first and second claddings, the diameter D₁ of said first cladding layer at said large diameter end being greater than d, whereby an enhanced enlargement of the mode field diameter of said single-mode signal is obtained,

means for positioning said first optical fiber at said large diameter end of said first modifier in light coupling relationship with said first modifier core,

means for positioning said second optical fiber at said large diameter end of said second modifier in light coupling relationship with said second modifier core, and

means for positioning the small diameter end of said first modifier adjacent the small diameter end of said second modifier with the axes of said first and second modifiers in substantial alignment.

6. A mode field modifier for use with an optical fiber having a core and a cladding of outside diameter d, said modifier comprising

a modifier core having a refractive index n₁,

a first cladding layer surrounding said modifier core, said first cladding layer having a refractive index n₂ that is less than n₁,

a second cladding layer on the surface of said first cladding layer, the refractive index n₃ of said second cladding layer being less than n₂, the ratio (n₂ -n₃)/n₂ being no smaller than 0.5%, said modifier being tapered intermediate its ends whereby it has a large diameter end and a small diameter end, the diameters of at least said core and said first cladding layer at said large diameter end are greater than the corresponding diameters at said small diameter end, whereby the mode field of an optical signal propagating in one end of said modifier is modified as said signal propagates through the tapered portion of said modifier, the diameter D₁ of said first cladding layer at said large diameter end being greater than d, and

means for positioning a fiber at said large diameter end in light coupling relationship with said modifier core.

7. A mode field modifier for use with an optical fiber having a core and a cladding of outside diameter d, said modifier comprising

a modifier core having a refractive index n₁,

a first cladding layer surrounding said modifier core, said first cladding layer having a refractive index n₂ that is less than n₁,

a second cladding layer on the surface of said first cladding layer, the refractive index n₃ of said second cladding layer being less than n₂, said modifier being tapered intermediate its ends whereby it has a large diameter end and a small diameter end, the diameters of at least said core and said first cladding layer at said large diameter end are greater than the corresponding diameters at said small diameter end, whereby the mode field of an optical signal propagating in one end of said modifier is modified as said signal propagates through the tapered portion of said modifier, the diameter D₁ of said first cladding layer at said large diameter end being greater than d, and

means for positioning a fiber at said large diameter end in light coupling relationship with said modifier core, said fiber forming the central portion of said mode field modifier and said first cladding layer comprising the cladding of said fiber and a further layer on the surface of said fiber cladding, said further layer having a refractive index equal to or less than that of said fiber cladding.

8. A mode field modifier for use with an optical fiber having a core and a cladding of outside diameter d, said modifier comprising

a modifier core having a refractive index n₁,

a first cladding layer surrounding said modifier core, said first cladding layer having a refractive index n₂ that is less than n₁,

a second cladding layer on the surface of said first cladding layer, the refractive index n₃ of said second cladding layer being less than n₂, said modifier being tapered intermediate its ends whereby it has a large diameter end and a small diameter end, the diameters of at least said core and said first cladding layer at said large diameter end being greater than the corresponding diameters at said small diameter end, the diameters of said core and first cladding layer at said small diameter end being sufficiently small that the field of a signal propagating in said large diameter end of said coupler toward the small diameter end thereof is no longer confined to said core and first cladding but it spreads and is effectively guided by the waveguide consisting of said first and second claddings, the diameter D₁ of said first cladding layer at said large diameter end being greater than d, whereby an enhanced enlargement of the mode field diameter of said single-mode signal is obtained, and

means for positioning a fiber at said large diameter end in light coupling relationship with said modifier core.

9. A mode field modifier for use with a single-mode optical fiber having a core and a cladding of outside diameter d, said modifier comprising

a modifier core having a refractive index n₁,

a first cladding layer surrounding said modifier core, said first cladding layer having a refractive index n₂ that is less than n₁,

a second cladding layer on the surface of said first cladding layer, the refractive index n₃ of said second cladding layer being less than n₂, said modifier being tapered intermediate its ends whereby it has a large diameter end and a small diameter end, the diameters of at least said core and said first cladding layer at said large diameter end being greater than the corresponding diameters at said small diameter end, the diameters of said core and first cladding layer at said small diameter end being sufficiently small that the field of a single-mode signal propagating in said core and first cladding layer at said large diameter end of said coupler toward the small diameter end thereof is no longer confined to said core and first cladding but it spreads and is effectively guided by the waveguide consisting of said first and second claddings, the diameter D₁ of said first cladding layer at said large diameter end being greater than d, whereby an enhanced enlargement of the mode field diameter of said single-mode signal is obtained, and

means for positioning a fiber at said large diameter end in light coupling relationship with said modifier core.