High fibre count blown optical fibre unit and method of manufacturing

Abstract

An optical fiber unit for air-blown installations includes a plurality of optical fiber sub-units and a central member, wherein the optical fiber sub-units are stranded around the central member; wherein each of the optical fiber sub-units includes a number of optical fibers, an inner layer which is radially outer to the optical fibers, and an outer layer which is radially outer to the inner layer, wherein the outer layer includes particulate material which is partially embedded into the outer layer; and wherein the optical fiber unit further includes a binder for keeping the stranded optical fiber sub-units in a proper arrangement.

Claims

1. An optical fiber unit for air-blown installations comprising a plurality of optical fiber sub-units and a central member, wherein said optical fiber sub-units are stranded around said central member; wherein each of said optical fiber sub-units comprises a number of optical fibres, an inner layer which is radially outer to the optical fibres, and an outer layer which is radially outer to the inner layer, and wherein the outer layer comprises particulate material which is partially embedded into the outer layer; and wherein said optical fiber unit has an outer surface and further comprises a binder for keeping said stranded optical fiber sub-units in a proper arrangement, wherein said binder covers at least a portion of the outer surface of said optical fiber unit and is the outermost layer of said optical fiber unit where present.

2. The optical fiber unit of claim 1, wherein said optical fiber sub-units are stranded around said central member in a SZ formation.

3. The optical fiber unit of claim 2, wherein said optical fiber sub-units are stranded around said central member by a lay length between 250 mm and 500 mm.

4. The optical fiber unit of claim 1, wherein said binder comprises an elongate member helically continuously wound in one direction around said stranded optical fiber sub-units.

5. The optical fiber unit of claim 1, wherein said binder comprises an elongate member helically continuously wound in two opposite directions so that a crossed arrangement is obtained.

6. The optical fiber unit of claim 4, wherein said binder comprises a binder tape.

7. The optical fiber unit of claim 6, wherein said binder tape covers about 15% to 50% of the outer surface of said optical fiber unit.

8. The optical fiber unit of claim 1, wherein said optical fiber unit comprises four optical fiber sub-units, each optical fiber sub-unit comprising six optical fibers.

9. The optical fiber unit of claim 1, wherein said optical fiber unit further comprises additional fillers.

10. The optical fiber unit of claim 9, wherein said additional fillers are stranded around said central member.

11. A method of manufacturing an optical fiber unit for air-blown installations, comprising: providing a plurality of optical fiber sub-units and a central member, wherein each of said optical fiber sub-units comprises a number of optical fibres, an inner layer which is radially outer to the optical fibres and an outer layer which is radially outer to the inner layer, wherein the outer layer comprises particulate material which is partially embedded into the outer layer; stranding said optical fiber sub-units around said central member; and binding said stranded optical fiber sub-units in a proper arrangement, wherein said optical fiber unit has an outer surface and wherein said binding covers at least a portion of the outer surface of said optical fiber unit and is the outermost layer of said optical fiber unit.

12. The method of claim 11, wherein said stranding comprises stranding said optical fiber sub-units around said central member in a SZ formation.

13. The method of claim 12, wherein said stranding comprises stranding by a lay length between 250 mm and 500 mm.

14. The method of claim 11, wherein said binding comprises winding an elongate member helically continuously in one direction around said stranded optical fiber sub-units.

15. The method of claim 11, wherein said binding comprises winding an elongate member helically continuously in two opposite directions around said stranded optical fiber sub-units so that a crossed arrangement is obtained.

16. The method of claim 14, wherein said binding comprises winding a binder tape.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will become more clear from the detailed following description, given by way of example and not of limitation, with reference to the following figures, wherein:

(2) FIG. 1 is a schematic cross-section of a blown optical fibre unit according to a first example of the present invention;

(3) FIG. 2 shows a length of the cable of FIG. 1 with a first type of binder;

(4) FIG. 3 shows a length of the cable of FIG. 1 with a second type of binder;

(5) FIG. 4 is a schematic cross-section of a blown optical fibre unit according to a second example of the present invention;

(6) FIG. 5 shows a length of the cable of FIG. 4 with a first type of binder; and

(7) FIG. 6 shows a length of the cable of FIG. 4 with a second type of binder.

DESCRIPTION OF EXAMPLES

(8) FIG. 1 represents a schematic cross-section of a blown optical fibre unit 1 according to a first example of the present invention.

(9) The optical fiber unit 1 comprises a plurality of optical fiber sub-units 2. In the example of FIG. 1 four optical fiber sub-units 2 are provided. However, in other examples (not shown) the number of optical fiber sub-units 2 could be higher or lower than four.

(10) Preferably, each of the optical fiber sub-units 2 is substantially as the other optical fiber sub-units. However, within the scope of protection of the present invention are also examples wherein the sub-units differ in terms of, for instance, number of optical fibers, outer diameter, material of the outer layer and surface coverage of the particulate material.

(11) Each of the optical fiber sub-units 2 preferably comprises a number of optical fibers 3, an inner layer 4 which is radially outer to the optical fibers 3 and an outer layer 5 which is radially outer to the inner layer 4. The outer layer 5 comprises particulate material 6 which is partially embedded into the outer layer.

(12) The term optical fibre is meant to indicate an optical glass core surrounded by a glass cladding and a coating system comprising one or two layers of cured resins, for example acrylate resins. The optical fibers may be single mode or multimode optical fibers with a nominal diameter between about 200 m and 250 m. Relative to each other, the optical fibers may have a length difference of less than about 0.03%. The optical fibers generally extend in a longitudinal direction but have no fixed position relative to inner layer 4.

(13) Each optical fiber sub-units 2 of the example of FIG. 1 comprises six optical fibers. In other examples (not shown), there are provided more than six optical fibers. In other examples (not shown), there are provided less than six optical fibers.

(14) Particulate material 6 can comprise any material which provides low friction when the optical fibre unit 1 is blown in a duct or micro-duct.

(15) For example, the particulate material 6 could be selected among beads of glass, of ceramic, of polytetrafluoroethylene (PTFE) or of high-density polyethylene (HDPE). The beads can be either hollow or solid. The beads may have a diameter of from 0.070 mm to 0.150 mm.

(16) The particle material coveragei.e. the amount of beads per unit surface area of the productin the optical fibre sub-unit 2 can be of from 15 to 35 beads/mm.sup.2.

(17) The embedding is the amount of sinking of the particles into the outer layer 5, expressed as percentage of the particle dimension which is embedded into the outer layer. According to examples of the invention, the embedding of the particle material is of from 20% to 70%, preferably from 20% to 60%. The embedding should be high enough to maintain the particle fixed into the outer layer, but not too much so as to compromise the surface roughness parameter. As a matter of fact, a relatively high surface roughness reduces the friction between the optical fiber unit and the duct during the blowing procedure and increases the ability of the optical fiber unit to be entrained by the air blowing.

(18) As said above, inner layer 4 is arranged radially outer to the optical fibers 3. Profitably, inner layer 4 comprises a layer of cured resin such as, for instance, acrylate resin. The diameter of inner layer 4 could be in a range between 0.6 mm and 1.3 mm, preferably between 0.8 mm and 1.2 mm. Example of a material for the inner layer 4 is Cabelite 3287-9-39A from DSM Desotech.

(19) Outer layer 5 is radially outer to the inner layer 4. Profitably, outer layer 5 comprises a layer of cured resin such as, for instance, acrylate resin. The outer diameter of outer layer 5 could be in a range between 0.7 mm and 2 mm, preferably between 1.0 mm and 1.4 mm. Outer layer 5 is generally harder than inner layer 4. Example of a material for the outer layer 5 is Cabelite 3287-9-75 from DSM Desotech.

(20) With further reference to FIG. 1, the optical fiber unit 1 further comprises a central member 7. Such central member 7 could be any of a glass reinforced plastic filler, a water swellable yarn or a strength member, possibly made of aramid or the like. Advantageously, central member 7 has a diameter in a range between 0.4 mm and 1.0 mm, preferably between 0.5 mm and 0.7 mm.

(21) According to an example of the present invention, the optical fiber sub-units 2 and the central member are stranded together. Stranding could be in a S formation. More preferably, the optical fiber sub-units 2 are stranded around the central member 7 in a SZ formation. Such arrangement is shown in FIGS. 2 and 3. The SZ stranding results in a stiffness reduction of the blown optical unit which, in turn, improves blowing performance.

(22) In case of a SZ stranding pattern, the optical fiber sub-units 2 are wound around the central member 7 in a first direction for one or several turns and then are wound around the central member for a corresponding number of turns in the opposite direction. The optical fiber sub-units 2 are wound around the central member 7 by a lay length between 250 mm and 500 mm. A typical lay length is about 300 mm.

(23) With further reference to FIG. 1, preferably the blown optical fiber unit 1 preferably comprises a binder 8 around the assembly comprising the optical fiber sub-units 2 wound around the central member 7.

(24) In examples of the invention, such binder 8 comprises an elongate member such as a binder yarn, a binder thread, a binder tape or the like.

(25) FIG. 2 shows a binder tape 8 wrapped around the assembly comprising the optical fiber sub-units 2 wound around the central member 7.

(26) In examples of the invention, binder tape 8 can be made of polyester, paper or the like. The binder tape 8 may be about 0.10 mm thick and about 30 mm large.

(27) Preferably, binder tape 8 is helically wound around the assembly comprising the optical fiber sub-units 2 wound around the central member 7.

(28) In a first example, shown in FIG. 2, one single binder tape 8 is helically continuously wound in one direction.

(29) In a second example, shown in FIG. 3, two binder tapes 8 are helically continuously wound in two opposite directions so that a crossed arrangement is obtained. This second example keeps the package more tight.

(30) In any case, according to preferred examples of the invention, the binder tape(s) does/do not cover the entire outer surface of the assembly. This in order not to cover all the particle material (beads) projecting from the harder outer layer. Preferably, the binder tape(s) is/are arranged in such a way that from about 15% to 50% of the outer surface becomes covered.

(31) Examples of optical fiber units according to the invention are: i) 2.4 mm diameter 24 fiber unit consisting of 4 subunits with 6 optical fibers having a weight of about 4.0 g/m and a stiffness of about 26.3 E-5 Nm.sup.2. The Applicant has found that such unit can be blown with good performance in ducts with a minimum inner diameter of 4.0 mm, without getting stuck in bends. ii) 3.0 mm diameter 48 fiber unit consisting of 4 subunits with 12 optical fibers having a weight of about 9 g/m and a stiffness of about 75 E-5 Nm.sup.2. The Applicant has found that such unit can be blown with good performance in ducts with an minimum inner diameter of 5.0 mm, without getting stuck in bends. iii) 4.3 mm diameter 72 fiber unit consisting of 6 subunits with 12 optical fibers having a weight of about 14 g/m and a stiffness of about 100 E-5 Nm.sup.2. The Applicant has found that such unit can be blown with good performance in ducts with a minimum inner diameter of 6.0 mm, without getting stuck in bends. iv) 5.3 mm diameter 96 fiber unit consisting of 8 subunits with 12 optical fibers having a weight of about 18 g/m and a stiffness of about 150 E-5 Nm.sup.2. The Applicant has found that such unit can be blown with good performance in ducts with a minimum inner diameter of 8.0 mm, without getting stuck in bends.

(32) Comparative mini cables with equal fiber counts would have diameters and weights of 5.0 mm and 22 g/m for a 24, 48 or 72 fiber unit, with a stiffness of about 0.5 Nm.sup.2. A 96 fiber count mini cable would have a diameter of 5.8 mm, a weight of 32 g/m and a stiffness of about 1 Nm.sup.2.

(33) Examples of fiber types which can be used in the units according to the invention are: Standard singlemode Fibre (SSMF) compliant with ITU-T Recommendation G.652, Table B) Enhanced singlemode Fibre (ESMF) compliant with ITU-T Recommendation G.652, Table D) bend insensitive single mode fiber (BI-SMF) compliant with ITU-T Recommendation G.652, Table D and ITU-T Recommendation G. 657 Graded index multimode fiber

(34) Such optical fibers are typically provided with a dual layer protective coating with a diameter of about 245 m. Alternatively, reduced diameter fibers could be used, with typical diameter (of the fiber with coating) between 190 and 210 m. This allows for a further reduction of the subunit diameter and hence the whole outer diameter of the unit.

(35) Reference is now made to FIGS. 4, 5 and 6 which show a second example of the present invention. Indeed, the second example has several similarities with the first example and a full detailed description will be omitted. The same reference signs will be used for indicating the same part or a technically equivalent component.

(36) Briefly, the optical fiber unit 1 of the second example comprises a plurality of optical fiber sub-units 2. Each of the optical fiber sub-units 2 comprises a number of optical fibers 3, an inner layer 4 which is radially outer to the optical fibers 3 and an outer layer 5 which is radially outer to the inner layer 4. The outer layer 5 comprises particulate material 6 which is partially embedded into the outer layer.

(37) The optical fiber unit 1 of the second example further comprises a central member 7. Such central member 7 could be any of a glass reinforced plastic filler, a water swellable yarn or a strength member, possibly made of aramid or the like. Advantageously, central member 7 has a diameter in a range between 0.4 mm and 1.0 mm, preferably between 0.5 mm and 0.7 mm.

(38) As can be inferred from a comparison between FIG. 1 and FIG. 4, the blown optical fiber unit 1 of the second example further comprises additional fillers 71. Preferably, an additional filler is arranged between two optical fiber sub-units 2. Therefore, with four optical fiber sub-units 2, four additional fillers 71 are provided.

(39) The presence of additional fillers 71 improves the circularity of the optical fiber unit 1. Additional fillers 71 could be in the form of polymeric or water swellable yarns. Additional fillers are stranded together with optical fiber sub-units 2.

(40) The Applicant has conducted test trials confirming the good performance of the optical fiber unit according to the invention.

(41) A 24f epfu (wherein epfu stands for enhanced performance fiber optical unit and 24f stands for 24 fibers), having a diameter of about 2.4 mm and consisting of 4 times a 6f epfu (1.1 mm diameter) SZ stranded around a central aramid or polyester member (0.5 mm diameter) and surrounded by a helical wrapped binder yarn, providing a coverage of 50% was blown into 500 m of 5.5 mm bore micro-ducting wound onto a drum at a constant speed of about 25 m/min at a blowing pressure of about 10 bar. Blowing performance is indicated in Table 1 below.

(42) TABLE-US-00001 TABLE 1 Blowing Performance Distance Speed Time [m] [m/min] [min] 0 0 0.00 50 25 2.10 100 25 4.12 150 25 6.12 200 25 8.12 250 24 10.16 300 23 12.25 350 20 14.30 400 25 16.35 450 25 18.35 500 25 20.35

(43) In the blown optical fiber unit 1 according to the present invention the optical fibers could be replaced by conventional loose tube packages or plastic coated blown fibre units, comprising a number of optical fibers (for instance 3+9 optical fibers), an inner sheath and an outer sheath.

(44) According to a second aspect, the present invention provides a method of manufacturing a blown optical fibre unit 1. The method comprises: providing a plurality of optical fiber sub-units and a central member, wherein each of said optical fiber sub-units comprises a number of optical fibers, an inner layer which is radially outer to the optical fibers and an outer layer which is radially outer to the inner layer, wherein the outer layer comprises particulate material which is partially embedded into the outer layer; stranding said optical fiber sub-units around said central member; binding said stranded optical fiber sub-units in a proper arrangement.