Undersea telecommunications cable

• US 6,496,629 B2
• Filed: 10/01/1999
• Issued: 12/17/2002
• Est. Priority Date: 05/28/1999
• Status: Expired due to Term

• Current Assignee: SubCom, LLC
• Original Assignee: Tycom Limited (Johnson Controls International plc)
• Inventors: Zhong, Qian, Ma, Chung Shin
• Primary Examiner(s): Ullah, Akm E.
• Application Number:
  US09/410,578
• Publication Number:
  US 20020044750A1
• Time in Patent Office: 1,173 Days
• Field of Search: 385/100-113, 385/147
• US Class Current: 385/113
• CPC Class Codes: G02B 6/4427 Pressure resistant cables, e.g. undersea cables
• CPC Class Codes: G02B 6/44384 the means comprising water blocking or hydrophobic materials G02B6/4439, G02B6/4479 take precedence

Abstract

An undersea telecommunications cable comprises a buffer tube which protects a plurality of optical fibers disposed therein from externally applied forces. To this end, the buffer tube contains a thixotropic, water blocking gel that has a viscosity and a critical yield shear stress sufficient to couple, upon application of a tensile load capable of producing up to a 0.8% strain in the cable, tensile forces from the buffer tube to the optical fibers to thereby induce strain in the fibers that is proportional to that induced in the tube, without preventing the return of the optical fibers to a substantially unstrained condition upon the removal of such tensile load. Should it become necessary to repair a section of the undersea cable as by retrieving it from the sea bed and inserting a spliced segment, existing sections of the fiber will be sufficiently protected from any damage which might otherwise have been caused during the cable retreival and recovery operation.

Claims

1. An undersea telecommunications cable having a plurality of optical fibers comprising:

a buffer tube defining an interior bore dimensioned and arranged to receive and protect said plurality of optical fibers from externally applied forces, said buffer tube further containing a thixotropic, water blocking gel having, at 25°

C., a critical yield shear stress of from 0.003 to 0.010 psi and a cone/plate viscosity of between 20,000 and 40,000 centipoise;

a series of strength members arranged in at least one layer around the buffer tube to withstand hydrostatic forces and traction on said cable during deployment and recovery; and

a plastic jacket surrounding said buffer tube and strength members, wherein said gel is adapted to loosely couple a tensile load applied to the buffer tube to said optical fibers while allowing said fibers to return to a substantially unstrained condition upon the removal of such tensile load.

2. The undersea telecommunications cable of claim 1, wherein said optical fibers have an average excess fiber length of from 0 to 0.1%.

3. The undersea telecommunications cable of claim 2, wherein said optical fibers have an average excess fiber length of from 0 to 0.05%.

4. The undersea telecommunications cable of claim 1, wherein the buffer tube is formed from one of polybutylene terephthalate and polycarbonate.

5. The undersea telecommunications cable of claim 1, wherein said strength members are arranged in at least two concentric layers in a close fitting relationship.

6. The undersea telecommunications cable of claim 1, wherein said water blocking gel has a fill ratio of at least 87%.

7. The undersea telecommunications cable of claim 1, wherein said water blocking gel is a synthetic oil having particles of fumed silica-colloidally dispersed therein.

8. The undersea telecommunications cable of claim 1, further including an electrical conductor concentrically disposed between said series of strength members and said plastic jacket.

9. The undersea telecommunications cable of claim 1, wherein said series of strength members comprises a layer of steel wires helically wound about an exterior surface of said buffer tube.

10. An undersea telecommunications cable having a plurality of optical fibers comprising:

a buffer tube defining an interior bore dimensioned and arranged to receive and protect said plurality of optical fibers from externally applied forces, said buffer tube further containing a thixotropic, water blocking gel adapted to resist the ingress of water in the event of damage to said cable;

a series of strength members arranged around the buffer tube;

an electrical conductor concentrically dispose around said series of strength members; and

a plastic jacket surrounding said buffer tube, strength members, and electrical conductors, wherein said gel has a viscosity and critical yield shear stress sufficient to couple, upon application of a tensile load to the cable producing up to a 0.8% cable strain, tensile forces to said optical fibers to thereby induce strain in the fibers proportional to that induced in the tube, while also allowing said fibers to return to a substantially unstrained condition upon the removal of such tensile load.

11. The undersea telecommunications cable of claim 10, wherein said gel has a critical yield shear stress in the range of from 0.003 psi to 0.01 psi.

12. The undersea telecommunications cable of claim 10, wherein said gel has a fill ratio of at least 87%.

13. The undersea telecommunications cable of claim 10, wherein said optical fibers have an average excess fiber length of from 0 to 0.1%.

14. The undersea telecommunications cable of claim 13, wherein said optical fibers have an average excess fiber length of from 0 to 0.05%.

15. The undersea telecommunications cable of claim 14, wherein the buffer tube is formed from one of polybutylene terephthalate and polycarbonate, and wherein the gel has a critical yield shear stress of from 0.003 psi to 0.010 psi.

16. The undersea telecommunications cable of claim 10, wherein said strength members are arranged in at least two concentric layers in a close fitting relationship.

17. An undersea telecommunications cable having a plurality of optical fibers comprising:

a hollow buffer tube having disposed therein said plurality of optical fibers and a thixotropic gel; and

a strengthening assembly concentrically disposed around said hollow buffer tube;

wherein said thixotropic gel has a viscosity and critical yield shear stress sufficient to couple, upon application of a tensile load to the cable producing up to a cable strain of up to 0.8%, tensile forces to said optical fibers to thereby induce strain in the fibers substantially proportional to that induced in the tube, while also allowing said fibers to return to a substantially unstrained condition upon the removal of such tensile load.

18. The undersea telecommunications cable of claim 17, wherein the average excess fiber length in the cable is less than 0.1%, wherein the viscosity of said thixotropic gel is less than around 32,000 centipoise at 25°

C., and wherein the critical yield shear stress is between from 0.003 to 0.010 psi.

19. The undersea telecommunications cable of claim 18, wherein the hollow buffer tube is comprised of polybutylene terephthalate and wherein the gel comprises a synthetic oil having particles of fumed silica colloidally suspended therein, said gel having a fill ratio by volume of at least 87%.

20. The undersea telecommunications cable of claim 17, wherein the viscosity and critical yield shear stress of said thixotropic gel are such that forces coupled between said buffer tube and said optical fibers are insufficient to cause any substantial increase in the attenuation of signals traversing said optical fibers, after said tensile load is released.