Compressible layer for fiber optic cable

• US 7,016,585 B2
• Filed: 05/04/2004
• Issued: 03/21/2006
• Est. Priority Date: 05/04/2004
• Status: Expired due to Fees

• Current Assignee: AT&T Intellectual Property I LP (AT&T, Inc.)
• Original Assignee: Bellsouth Intellectual Property Corporation (AT&T, Inc.)
• Inventors: Diggle, Frederick III, Ryals, Steven
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): Stein, James D.
• Application Number:
  US10/838,661
• Publication Number:
  US 20050249472A1
• Time in Patent Office: 686 Days
• Field of Search: 385125-127, 385/128
• US Class Current: 385/128
• CPC Class Codes: G02B 6/4432 with fibre reinforcements
• CPC Class Codes: G02B 6/44386 Freeze-prevention means G02B6/4439, G02B6/4479 take precedence

Abstract

A layered fiber optic cable having a compressible layer for protecting the fiber optic core from damaging displacement due to force from the freezing of trapped ambient water. As ambient water within a protective conduit freezes, the water expands, applying a force on the fiber optic cable within the conduit. The compressible layer absorbs the expansion of the freezing water by compressing, therefore minimizing displacement of the fiber optic core and resulting signal degradation.

Claims

1. A layered fiber optic cable for being placed in a conduit, the fiber optic cable comprising:

at least one strand of optical fiber forming an axial core of the fiber optic cable;

at least one layer of strengthening material surrounding the at least one strand of optical fiber;

a jacket encompassing the at least one strand of optical fiber and the at least one layer of strengthening material; and

at least one compressible layer of material encompassing the at least one strand of optical fiber, wherein the compressible layer of material is configured to compress the at least one strand of optical fiber in response to an application of force due to freezing of water surrounding the fiber optic cable, such that, for a maximum amount of freezing water capable of forming between the conduit and the layered fiber optic cable, the thickness and the compressible characteristics of the compressible layer of material being selected to cause the compressible layer of material to minimize displacement of the at least one strand of optical fiber in response to the application of force.

2. The layered fiber optic cable of claim 1 wherein the strengthening material is aramid yarn.

3. The layered fiber optic cable of claim 1 wherein the compressible layer of material comprises neoprene.

4. The layered fiber optic cable of claim 1 wherein the compressible layer of material comprises closed cell foam.

5. The layered fiber optic cable of claim 2 further comprising:

a fiber coating layer surrounding the at least one strand of optical; and

a plastic overcoat layer surrounding the at least one strand of optical fiber.

6. The layered fiber optic cable of claim 1, wherein the at least one compressible layer of material is disposed between the at least one layer of strengthening material and the jacket.

7. The layered fiber optic cable of claim 1, wherein the at least one compressible layer of material is disposed between the at least one layer of strengthening material and the optical fiber core.

8. The layered fiber optic cable of claim 1, wherein the at least one compressible layer of material has elastic characteristics so that the compressible layer of material returns substantially to its original shape upon removal of the force.

9. A method for forming a layered fiber optic cable configured to be placed in a conduit, the method comprising:

providing at least one strand of optical fiber such that the at least one strand forms an axial core of the cable;

providing at least one layer of strengthening material around the at least one strand of optical fiber;

providing at least one compressible layer of material around the at least one strand of optical fiber, wherein the compressible layer of material is configured to compresses the at least one strand of optical fiber in response to an application of force due to freezing of water surrounding the fiber optic cable, such that, for a maximum amount of freezing water capable of forming between the conduit and the layered fiber optic cable, the thickness and the compressible characteristics of the compressible layer of material being selected to cause the compressible layer of material to minimize displacement of the at least one strand of optical fiber in response to the application of force; and

providing a jacket around all of the layers of the fiber optic cable.

10. The method of claim 9 wherein the strengthening material is aramid yarn.

11. The method of claim 9 wherein the compressible layer of material comprises neoprene.

12. The method of claim 9 wherein the compressible layer of material comprises closed cell foam.

13. The method of claim 10 further comprising:

providing a fiber coating layer surrounding the optical fiber axial core; and

providing a plastic overcoat layer surrounding the optical fiber axial core.

14. The method of claim 9, wherein the at least one compressible layer of material is disposed between the at least one layer of strengthening material and the jacket.

15. The method of claim 9, wherein the at least one compressible layer of material is disposed between the at least one layer of strengthening material and the optical fiber core.

16. The method of claim 9, wherein the at least one compressible layer of material has elastic characteristics so that the material of the compressible layer returns substantially to its original shape upon removal of the force.

17. A layered fiber optic cable configured to be placed in a conduit, the cable comprising:

at least one strand of optical fiber forming an axial core of the fiber optic cable;

a fiber coating layer surrounding the at least one strand of optical fiber;

a plastic overcoat layer surrounding the fiber coating layer;

an aramid yarn layer surrounding the plastic overcoat layer;

a compressible layer of material surrounding the aramid yarn layer, wherein the compressible layer of material is configured to compress the at least one strand of optical in response to an application of force due to freezing of water surrounding the fiber optic cable, such that, for a maximum amount of freezing water capable of forming between the conduit and the layered fiber optic cable, the thickness and the compressible characteristics of the compressible layer of material being selected to cause the compressible layer of material to minimize displacement of the at least one strand of optical fiber in response to the application of force; and

a jacket encompassing all layers of the fiber optic cable.

18. The layered fiber optic cable of claim 17 wherein the compressible layer of material comprises neoprene.

19. The layered fiber optic cable of claim 17 wherein the compressible layer of material comprises closed cell foam.

20. The layered fiber optic cable of claim 17, wherein the at least one compressible layer of material has elastic characteristics so that the material returns substantially to its original shape upon removal of the force.