Blown Optical Fiber Unit and Method of Manufacturing

Abstract

In one embodiment, an air-blown optical fiber unit includes one or more optical fibers, an inner layer substantially completely embedding the one or more optical fibers, and an outer layer radially external to the inner layer. The inner layer has a tensile strength of from 0.1 MPa to 1 MPa, and an elongation at break of from 10% to 80%.

Claims

1-15. (canceled)

16. An air-blown optical fiber unit comprising: one or more optical fibers; an inner layer substantially completely embedding the one or more optical fibers; and an outer layer radially external to the inner layer, wherein the inner layer has a tensile strength of from 0.1 MPa to 1 MPa, and an elongation at break of from 10% to 80%.

17. The optical fiber unit of claim 16, wherein the optical fiber unit comprises one to twenty four optical fibers.

18. The optical fiber unit of claim 16, wherein the inner layer has a tensile strength of from 0.5 MPa to 0.9 MPa.

19. The optical fiber unit of claim 16, wherein the inner layer has an elongation at break of from 20% to 35%.

20. The optical fiber unit of claim 16, wherein the inner layer has a Shore A hardness of from 10 to 40.

21. The optical fiber unit of claim 16, wherein the inner layer has a 2.5% secant modulus of from 1 MPa to 10 MPa.

22. The optical fiber unit of claim 16, wherein the outer layer has a Shore D hardness of from 30 to 80.

23. The optical fiber unit of claim 16, wherein the outer layer has tensile strength of from 10 MPa to 60 MPa.

24. The optical fiber unit of claim 16, wherein the outer layer has a 2.5% secant modulus of from 500 MPa to 1000 MPa.

25. The optical fiber unit of claim 16, further comprising an ink layer in radially outer position with respect to the outer layer and in direct contact thereto.

26. The optical fiber unit of claim 25, wherein the ink layer has a Shore D hardness of from 40 to 90.

27. The optical fiber unit of claim 16, wherein the optical fiber unit has an outer diameter of at most 890 m and comprises four optical fibers having a diameter of 250 m.

28. The optical fiber unit of claim 16, wherein each of the one or more optical fibers comprises: an optical waveguide; a cladding surrounding the optical waveguide; a first polymeric coating surrounding the cladding; a second polymeric coating surrounding the first polymeric coating; and a third polymeric coating surrounding the second polymeric coating.

29. An air-blown optical fiber unit comprising: an optical fiber comprising an optical waveguide; an inner layer surrounding the optical fiber; an outer layer radially external to the inner layer; an ink layer disposed around the outer layer; a plurality of beads disposed in the outer layer and extending through the ink layer, wherein the inner layer has a tensile strength of from 0.1 MPa to 1 MPa, and an elongation at break of from 10% to 80%.

30. The optical fiber unit of claim 29, wherein the optical fiber comprises: a cladding surrounding the optical waveguide; a first polymeric coating surrounding the cladding; a second polymeric coating surrounding the first polymeric coating; and a third polymeric coating surrounding the second polymeric coating.

31. The optical fiber unit of claim 29, wherein the optical fiber unit further comprises a plurality of optical fibers, wherein a total number of optical fibers in the optical fiber unit is between two and twenty four.

32. A method of manufacturing an air-blown optical fiber unit, the method comprising: providing one or more optical fibers; applying an inner layer on the one or more optical fibers; applying an outer layer; curing the inner layer to provide a tensile strength of from 0.1 MPa to 1 MPa and an elongation at break of from 10% to 80%; and curing the outer layer.

33. The method of claim 32, wherein the applying an inner layer on the one or more optical fibers is carried out at a temperature of from 15 C. to 30 C.

34. The method of claim 32, wherein the outer layer is applied on an uncured inner layer and then the inner and outer layers are simultaneously cured.

35. The method of claim 32, further comprising providing an ink layer in radially outer position with respect to the outer layer and in direct contact thereto, wherein the ink layer has a Shore D hardness of from 40 to 90.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The present invention will be further described in the following detailed description, given by way of example and not of limitation, with reference to the following figures, wherein:

[0051] FIG. 1 shows a cross-section of a blown optical fiber unit according to a first example of the present invention; and

[0052] FIG. 2 shows a cross-section of a blown optical fiber unit according to a second example of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0053] The present invention relates to optical fiber units for air-blown installations. In particular, the present invention relates to a blown optical fiber unit providing high performance in terms of accessibility of the optical fiber(s). The present invention also relates to a method of manufacturing such an optical fiber unit.

[0054] FIG. 1 shows a cross-section of a blown optical fiber unit 1 according to a first example of the present invention. The unit 1 comprises four optical fibers 2, an inner layer 10 and an outer layer 12.

[0055] It should be noticed that the number of optical fibers 2 is not relevant for the present invention and the number of optical fibers could be any number. Also an optical core with a single optical fiber is deemed within the scope of the present invention.

[0056] Each optical fiber 2 comprises a glass core comprising an optical waveguide 3, for example a single mode optical waveguide, and a cladding 4 surrounding the waveguide 3. A first polymeric coating 5 surrounds the cladding 4 and a second polymeric coating 6 surrounds the first polymeric coating 5. According to embodiments, each optical fiber 2 may further comprise a third polymeric coating 7, typically an ink layer, surrounding the second polymeric coating 6.

[0057] Preferably, the optical fibers 2 of the optical core are arranged in a bundle.

[0058] Each optical fiber 2 can have a fiber outer diameter of from 150 m to 300 m, preferably from 200 m to 245 m, when the third polymeric coating 7 is absent.

[0059] The third polymeric coating 7 could have a thickness of 5 m.

[0060] The blown optical fiber unit 1 according to the present invention further comprises an inner layer 10 embedding the optical fibers 2.

[0061] Preferably, the inner layer 10 of the embodiment of FIG. 1 (relating to an optical fiber unit 1 comprising four optical fibers 2 having an outer diameter of 255 m) has a diameter of 780 m.

[0062] The blown optical fiber unit 1 according to the present invention further comprises an outer layer 12 surrounding and in direct contact with the inner layer 10. The outer layer 12 of the embodiment of FIG. 1 (relating to an optical fiber unit 1 wherein the inner layer 10 has a diameter of 780 m) has an outer diameter 12 of 920 m.

[0063] The blown optical fiber unit 1 according to the present invention further preferably comprises an ink layer 13 surrounding the outer layer 12.

[0064] The ink layer 13 has a thickness of 10 m.

[0065] The Applicant has tested several materials for the inner buffer, with the object to reduce fiber breakout failure. A suitable material is Herkula Series 830/801, produced by Herkula Farben GmbH, Willich, Germany.

[0066] FIG. 2 is a cross-section of a second example of the present invention. In FIG. 2, the same reference numbers of FIG. 1 apply to the same cable parts. The blown optical fiber unit 1 of FIG. 2 comprises twelve optical fibers 2. The optical fiber unit 1 of FIG. 2 has beads 14 partially embedded in the outer layer 12. Beads 14 can be of glass or the like.

Test 1

[0067] The fiber breakout performance in an optical fiber unit according to the invention was tested as follows.

[0068] A first blown optical fiber unit according to the example of FIG. 1 was manufactured. The novel unit was made using Herkula Series 830/801 for the inner layer, so that this layer had a Shore A hardness of 28, a tensile strength of 0.6 MPa and an elongation at break of 30%.

[0069] The optical core comprised four optical fibers manufactured by different manufacturers. The four fibers were embedded in the inner layer made of Herkula Series 830/801 at a temperature of 27 C. An outer buffer made of DSM Cablelite 3287-9-75 was applied over the inner layer.

[0070] A second blown optical fiber unit according to the example of FIG. 1 was manufactured. This second unit is a comparative one. The optical core comprised the same four optical fibers of the first unit but embedded in an inner layer made of DSM 3287-9-39A having a tensile strength of 1.3 MPa and an elongation at break of 135% and DSM Cablelite 3287-9-75 for the outer layer. The application of the inner layer was carried out at a temperature of 40 C.

[0071] Different temperatures for the application of the inner layers of the first and of the second optical fiber unit were necessary for having the two materials at substantially the same viscosity.

[0072] The fiber breakout performance was evaluated according to the British Telecom standard CW1574, Issue 13 (1993), section 3.4.

[0073] Table 1 shows the results of Test 1.

TABLE-US-00001 TABLE 1 Fiber Second unit Breakout First unit Breakout Grey F P Violet P P White F P Orange P P P = positive F = failed

[0074] The first unit according to the invention reached a Positive grade, while only two fibers of the comparative second unit were considered positive in the test. Without being necessarily limited to any one particular explanatory theory, the Applicant considers that this extremely positive result has been obtained owing to the mechanical features of the inner layer according to the invention, especially in terms of tensile strength and elongation at break.

Test 2

[0075] The attenuation performance of the first blown optical fiber unit as from Test 1 was tested according to ITU-T G.652 (06/2005).

[0076] Attenuation results for first unit are indicated in Table 2 below.

TABLE-US-00002 TABLE 2 First Unit Fiber 1310 nm (dB/km) 1550 nm (dB/km) 1625 nm (dB/km) Grey 0.354 0.229 0.330 Violet 0.325 0.214 0.232 White 0.331 0.214 0.228 Orange 0.327 0.208 0.215

[0077] The attenuation of the optical fibers in the unit of the invention resulted in conformity with the values requested by of ITU-T G.652 (06/2005) standard, Table 4 (G.652.D). This test showed that, though the optical fibers of the unit of the invention were embedded in a soft inner layer, such inner layer was anyway suitable for protecting the fibers against attenuation. The material of the inner layer according to the invention provided improved fiber break-out with no detrimental effect to the optical performance.

Test 3

[0078] The blowing performance of a length of the first optical fiber unit of the invention as from Test 1 was tested according to the British Telecom standard CW1574 Issue 13 (1993), section 7.3.1.

[0079] The blow test was carried out under the following conditions/parameters, which is summarized in the tables below.

TABLE-US-00003 Blown Parameters Tube Emtelle FC6187624 Bore [mm] 3.5 nominal Tube Outside Diameter [mm] 5 No. of Times Used 14

TABLE-US-00004 Route Details Length [m] 500 (Internal ducted) Route Details Delivery drum Airflow @ [l/min] 11 bar

TABLE-US-00005 Test Details Compressor model 2 x Factair Comp. pressure/capacity 11.0 bar/120 l/min Blowing equipment details Plumettaz Pressure at input [bar] 9.80 Dewpoint [ C.] 24.8 Clutch Setting 4.00 Fiber Guide Brass Ambient temperature [ C.] 18 Weather conditions overcast, damp

TABLE-US-00006 Results Distance Blown [m] 500 Time [min] 20.15 Speed [m/min] 24.8

[0080] After blowing, the first optical fiber unit complied with the above mentioned standard in terms of optical fiber attenuation showing that the inner layer can provide the optical fibers with suitable protection during deployment.