OPTICAL CABLE

Abstract

An optical cable comprises a strength member element and a plurality of buffer tubes, wherein each of the buffer tubes encapsulates at least one optical fiber. The buffer tubes are stranded around the strength member element with subsequent different directions of lay. In order to fix the stranded buffer tubes and to prevent any unwinding of the stranded buffer tubes an adhesive component is disposed in at least one fixing area of the optical cable, the at least one fixing area being a regional area of the optical cable, where sections of the buffer tubes having a different direction of lay adjoin to each other.

Claims

1. An optical cable, comprising: a strength member element, a plurality of buffer tubes, wherein each of the buffer tubes encapsulates at least one optical fiber, wherein each of the buffer tubes has at least one first section and at least one second section adjacent to the at least one first section, wherein the at least one first section of the buffer tubes is stranded around the strength member element in a first direction of lay and the at least one second section of the buffer tubes is stranded around the strength member element in a second direction of lay opposite to the first direction of lay, an adhesive component disposed in at least one fixing area of the optical cable, the at least one fixing area being a regional area of the optical cable, where the at least one first section of the buffer tubes adjoins the at least one second section of the buffer tubes, wherein the buffer tubes are fixed to the strength member element by the adhesive component.

2. The optical cable of claim 1, wherein the direction of lay of the buffer tubes abruptly changes from the first direction of lay to the second direction of lay at a respective reversal point of the buffer tubes located in the at least one fixing area of the optical cable.

3. The optical cable of claim 1, wherein the buffer tubes are stranded around the strength member element such that the buffer tubes change their stranding direction at the reversal point in the at least one fixing area without being stranded unidirectional along the longitudinal direction of the optical cable.

4. The optical cable of claim 1, wherein each of the at least one first section (and the at least one second section of the buffer tubes has end portions and a middle portion located between the respective end portions, wherein one of the end portions of the at least one first section of the buffer tubes adjoins to one of the end portions of the at least one second section of the buffer tubes, wherein the at least one fixing area extends from the border between the middle portion and said one of the end portions of the at least one first section of the buffer tubes to the border between the middle portion and said one of the end portions of the at least one second section of the buffer tubes.

5. The optical cable of claim 4, wherein the end portions of the at least one first section of the buffer tubes and the end portions of the at least one second section of the buffer tubes are embedded in the adhesive component, and wherein the middle portion of each of the buffer tubes is uncovered by the adhesive component.

6. The optical cable of claim 1, wherein the at least one fixing area has a length of two to three times of the diameter of one of the buffer tubes.

7. The optical cable of claim 4, further comprising: at least a first, a second and a third fixing are, wherein the adhesive component is disposed in each of the at least one first and second and third fixing areas, wherein the first and the second fixing areas are disposed in a distance to each other along the longitudinal direction of the optical cable, wherein the distance has a length of a region of the optical cable in which the middle portion of the at least one first section of the buffer tubes is located, wherein the second and the third fixing areas are disposed in a distance to each other along the longitudinal direction of the optical cable, wherein the distance has the length of another region of the optical cable in which the middle portion of the at least one second section of the buffer tubes is located.

8. The optical cable of claim 1, comprising: a cable core comprising the strength member element, the buffer tubes and the adhesive component, a cable jacket surrounding the cable core, wherein the adhesive component is configured to block water from propagating between the cable core and the cable jacket along the buffer tubes in the longitudinal direction of the optical cable.

9. The optical cable of claim 8, wherein the adhesive component is disposed in the at least one fixing of the optical cable such that a first area of the optical cable between the buffer tubes and the strength member element and a second area of the optical cable between the buffer tubes and the cable jacket are completely filled up with the adhesive component.

10. The optical cable of claim 1, wherein the adhesive component is a glue.

11. The optical cable of claim 10, wherein the glue contains one of a thermoplastic polymer and/or an oil and/or a an emollient agent or any mixtures thereof

12. A method to manufacture an optical cable, comprising: providing a strength member element, stranding a plurality of buffer tubes having at least one first section and at least one second section adjacent to the at least one first section around the strength member element such that the at least one first section of the buffer tubes is stranded around the strength member element in a first direction of lay and the at least one second section of the buffer tubes is stranded around the strength member element in a second direction of lay opposite to the first direction of lay, injecting an adhesive component in at least one fixing area of the optical cable, the fixing area being an area of the optical cable, where the at least one first section of the buffer tubes adjoins to the at least one second section of the buffer tubes, and cooling the adhesive component to fix the buffer tubes to the strength member element.

13. The method of claim 12, further comprising: pressing the adhesive component in a first area of the optical cable between the buffer tubes and the strength member element and a second area of the optical cable between the buffer tubes and the cable jacket such that the first and second areas are completely filled up with the adhesive component.

14. The method of claim 12, further comprising: stranding the buffer tubes around the strength member element such that the direction of lay of the buffer tubes abruptly changes from the left direction of lay to the right direction of lay at a reversal point located in the at least one fixing area of the optical cable.

15. The method of claim 12, further comprising: stranding the buffer tubes around the strength member element such that the buffer tubes change their stranding direction in the at least one fixing area without being stranded unidirectional along the longitudinal direction of the optical cable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows an embodiment of a core section of an optical cable with stranded buffer tubes in a longitudinal view of the optical cable.

[0018] FIG. 2 shows an embodiment of an optical cable with stranded buffer tubes in a lateral cut of the optical cable.

[0019] FIG. 3 shows an embodiment of a manufacturing line to manufacture an optical cable with stranded buffer tubes.

[0020] FIG. 4 shows an embodiment of a caterpillar and torsion blocker of the manufacturing line in a lateral view.

[0021] FIG. 5A shows an embodiment of a stranding apparatus with injection nozzles for injecting an adhesive component to reversal points of the buffer tubes of the optical cable.

[0022] FIG. 5B shows an arrangement of injection nozzles to inject an adhesive component to reversal points of the buffer tubes of the optical cable.

DETAILED DESCRIPTION

[0023] FIG. 1 shows an embodiment of a core section 100 of an optical cable comprising a strength member element 110 and a plurality of buffer tubes 120 in a longitudinal view. Each of the buffer tubes 120 encapsulates at least one optical fiber 130. Each of the buffer tubes 120 has at least one first section 121 and at least one second section 122 adjacent to the at least one first section 121. The at least one first section 121 of the buffer tubes 120 is stranded around the strength member element 110 in a first direction of lay. The at least one second section 122 of the buffer tubes 120 is stranded around the strength member element 110 in a second direction of lay opposite to the first direction of lay. The first direction of lay may be a right direction of lay and the second direction of lay may be a left direction of lay or vice versa.

[0024] The core section 100 of the optical cable further comprises an adhesive component 140 disposed in at least one fixing area 151, 152, 153 of the optical cable. The buffer tubes 120 are fixed to the strength member element 110 by the adhesive component 140. The at least one fixing area 151, 152, 153 is a regional area of the optical cable where the adhesive component 140 is deposited to the reversal points of the stranded buffer tubes and where the at least one first section 121 of the buffer tubes 120 adjoins the at least one second section 122 of the buffer tubes. That means that the fixing areas and hence the adhesive component 140 do not extend along the entire length of the core section inside the cable. According to an embodiment of the optical cable, the at least one fixing area 151, 152 and 153 has a length of two to three times of the diameter of one of the buffer tubes 120.

[0025] Each of the at least one first section 121 of the buffer tubes 120 has end portions 121a, 121b and a middle portion 121c, and each of the at least one second section 122 of the buffer tubes 120 has end portions 122a, 122b and a middle portion 122c. One of the end portions of the at least one first section 121 of the buffer tubes, for example the end portion 121a, adjoins to one of the end portions of the at least one second section 122 of the buffer tubes, for example the end portion 122b. The at least one fixing area 151, 152, 153, extends from the border between the middle portion 121c and one of the end portions 121a, 121b of the at least one first section 121 of the buffer tubes to the border between the middle portion 122c and one of the end portions 122b, 122a of the at least one second section 122 of the buffer tubes. That means that the fixing areas 151, 152, 153 in which the adhesive component 140 is disposed completely extend over the respective end portions of the at least one first and second sections 121, 122 of the buffer tubes, but does not extend to the respective middle portions of the at least one first and second section 121, 122 of the buffer tubes.

[0026] The cutout of the optical core 100 shown in FIG. 1 comprises, for example, a fixing area 151, a fixing area 152 and a fixing area 153. The adhesive component 140 is disposed in each of the fixing areas 151, 152 and 153. The fixing area 151 and the fixing area 152 are disposed at a distance to each other along the longitudinal direction of the optical cable. The distance between the fixing areas 151, 152 has the length of a region of the optical cable in which the middle portion 121c of the at least one first section 121 of the buffer tubes 120 is located. The fixing area 152 and the fixing area 153 are also disposed at a distance to each other along the longitudinal direction of the optical cable. The distance between the fixing area 152 and the fixing area 153 has the length of another region of the optical cable in which the middle portion 122c of the second section 122 of the buffer tubes is located.

[0027] The stranded buffer tubes are fixed in the fixing areas 151, 152, 153 by the adhesive component 140 such that an unwinding of the buffer tubes is prevented. The fixing areas 151, 152 and 153 are the regions where the direction of lay of the buffer tubes changes from the first direction to the second direction and vice versa. The deposition of the adhesive component in the fixing areas 151, 152 and 153 allows that the buffer tubes may be stranded such that the direction of lay of the buffer tubes 120 abruptly changes from one direction of lay to the other direction of lay at a respective reversal point 160 of the buffer tubes, wherein the reversal point is a point-shaped position of the buffer tubes at which the direction of lay of the buffer tubes abruptly changes. The reversal point of the buffer tubes is located between the section of the buffer tubes having the first direction of lay and the subsequent section of the buffer tubes having the second direction of lay. A respective reversal point is located in each of the fixing areas 151, 152 and 153 of the optical cable 1.

[0028] The deposition of the adhesive component 140 in the fixing areas enables that the buffer tubes 120 are stranded such that the buffer tubes change their stranding direction at each reversal point 160 of the buffer tubes in the fixing areas 151, 152 and 153 without stranding the buffer tubes unidirectionally along the longitudinal direction of the optical cable 1. That means that by depositing the adhesive component 140 to the fixing areas it is possible to strand the optical fibers in one direction of lay, for example, a right direction of lay in the sections 121 of the buffer tubes and in another direction of lay, for example, a left direction of lay, in the subsequent sections 122 without being guided parallel to the longitudinal direction of the optical cable between reversal points 160 in subsequent fixing areas.

[0029] As shown in FIG. 1, the buffer tubes are stranded in section 121 with a positive inclination and are stranded in the adjacent section 122 with a negative inclination. In a portion of the section 121 far away from the reversal point 160 the buffer tubes are stranded with a constant positive inclination, for example an inclination of +70. In an adjacent portion of the section 121 of the buffer tubes which is next to the reversal point 160 the inclination of the buffer tubes slowly increases and reaches a maximum at the reversal point 160. In a portion of the adjacent section 122 of the buffer tubes next to the reversal point 160 the inclination of the buffer tubes slowly decreases again until the buffer tubes are stranded with constant negative inclination, for example an inclination of 70, at a portion of the section 122 of the buffer tubes far away from the reversal point 160.

[0030] A reversal length of the cable is specified as a longitudinal elongation of the cable between the section of the buffer tubes with the constant positive inclination, i.e. the minimum positive inclination, and the adjacent section of the buffer tubes with the constant negative inclination, i.e. the minimum negative inclination. The embodiment of the optical cable allows that the reversal length is lower than one lay length of the buffer tubes. That means that the method of fixing the buffer tubes by injecting the adhesive component 140 to the fixing areas allows to produce an optical cable having a reversal length of less than a range between 150 mm and 50 mm in dependence on the lay length of the buffer tubes.

[0031] FIG. 2 shows a lateral cut of an optical cable 1 comprising the core section 100 of FIG. 1. The lateral cut is shown at the position of the fixing area 152 marked in FIG. 1 by reference signs A-A. The cable core 100 of the optical cable 1 comprises the central strength member element 110, the buffer tubes 120 with the optical fibers 130 housed therein and the adhesive component 140. The optical cable further comprises a cable jacket 200 which surrounds the cable core 100.

[0032] According to an embodiment of the optical cable 1 as shown in FIG. 2, the adhesive component 140 is disposed at each of the fixing areas such that the end portions 121a, 121b of each of the first sections 121 of the buffer tubes and the end portions 122a, 122b of each of the second sections 122 of the buffer tubes are embedded in the adhesive component 140. The respective middle portion 121c, 122c of the at least one first and second sections 121, 122 of the optical cable is uncovered by the adhesive component 140.

[0033] The adhesive component 140 may be disposed in the at least one fixing area 151, 152 and 153 such that an area 101 of the optical cable between the buffer tubes 120 and the strength member element 110 and an area 102 of the optical cable between the buffer tubes 120 and the cable jacket 200 are completely filled up with the adhesive component 140. In particular, the adhesive component 140 may be configured to block water from propagating along the buffer tubes 120 in the longitudinal direction of the optical cable 1 between the cable core 100 and the cable jacket 200.

[0034] The adhesive component 140 may be a glue, for example a glue which comprises a thermoplastic polymer, such as polyurethane or polyester. The adhesive component may be a hot melt adhesive of a thermoplastic material. According to a possible embodiment the adhesive component may comprise an oil and/or an emollient agent or mixtures thereof. The properties of the adhesive component 140 may be adjusted by adding oils and/or emollient agents to the base material of a thermoplastic polymer so that, on the one hand the adhesive force of the adhesive component is sufficient to hold the buffer tubes 120 stranded with different directions of lay around the strength member element and, on the other hand, allows the removal of the adhesive component by hand for any installation of the optical cable without using additional tools.

[0035] Each of the buffer tubes 120 may have a diameter of 0.5 mm to 3.0 mm. Each of the buffer tubes may encapsulate 1 to 36 of the optical fibers 130. The buffer tubes may contain at least a material of one of polypropylene, polybutylene terephthalate, polyamide and fluoric synthetic materials as well as mixtures thereof. The material of the buffer tube may contain an organic or anorganic filler. The cable may comprise at least three to thirty of the buffer tubes. According to another embodiment the buffer tubes may be disposed in a multi-layer arrangement in the core section of the optical cable around the strength member element.

[0036] FIG. 3 shows an embodiment of a manufacturing line 2 to manufacture the optical cable 1. The manufacturing line 2 comprises a stranding and fixing apparatus 10 which receives the strength member element 110 and the plurality of buffer tubes 120. The stranding and fixing apparatus 10 is configured to strand the buffer tubes around the strength member element 110 such that the at least one first section 121 of the buffer tubes 120 is stranded around the strength member element 110 in the first direction of lay and the at least one second section 122 of the buffer tubes 120 is stranded around the strength member element 110 in the second direction of lay opposite to the first direction of lay.

[0037] The apparatus 10 is further configured to inject the adhesive component 140 in the fixing areas 151, 152, 153 of the optical cable 1, wherein the fixing areas are regional areas of the optical cable where the at least one first section 121 of the buffer tubes adjoins the at least one second section 122 of the buffer tubes. A low amount of the adhesive component 140 is injected to the fixing areas where the reversal points 160 of the buffer tubes are located. The point in time to inject the adhesive component 140 may be determined by the cycles in which the buffer tubes are stranded in the different directions of lay.

[0038] The core section 100 is further transported to a caterpillar and torsion blocker apparatus 20 located behind the stranding and fixing apparatus 10. According to the embodiment shown in FIG. 3, the manufacturing line 2 comprises caterpillar and torsion blocker devices 20a and 20b. Each of the caterpillar and torsion blocker devices comprises a roll unit 21 to move a caterpillar 22. The adhesive component 140 which is injected in the fixing areas 151, 152 and 153, and thus also in the reversal points 160, is immediately annealed by the cold material of the buffer tubes 120. Any excessive material of the adhesive component 140 is pressed in the interstices 101 and 102 by means of the respective caterpillar 22 of the caterpillar and torsion blocker devices 20a and 20b.

[0039] The caterpillar 22 may have several segments to enable an appropriate shaping of the core section 100. The caterpillar treads may be cooled so that the surface of the adhesive component is directly cooled down and any bonding with the caterpillar treads may be prevented. The cooling of the caterpillar treads may be effected by a cooling fluid and/or by air cooling from the outside.

[0040] After being transported through the caterpillar and torsion blocker devices 20a and 20b, the readymade cable core section 100 may be wound on a reel for further manufacturing or may be directly further processed, for example by extruding the cable jacket 200.

[0041] FIG. 4 may be a lateral view of the caterpillar and torsion apparatus 20 of FIG. 3 as seen from a view indicated in FIG. 3 with the reference signs B-B and shows an embodiment of four caterpillar and torsion blocker devices. The caterpillar and torsion blocker devices 20a and 20b may be moved in a vertical direction and the caterpillar and torsion blocker devices 20c and 20d may be moved in a horizontal direction. The arrangement of the caterpillar and torsion blocker apparatus 20 shown in FIG. 4 allows to manufacture optical cables having a cable core section 100 of different diameters.

[0042] FIG. 5A shows a schematic view of an embodiment of the stranding and fixing apparatus 10 which receives the buffer tubes 120. The stranding and fixing apparatus may comprise injection nozzles 11a, 11b for injecting the adhesive component 140 in the fixing areas and hence to the reversal points 160 of the buffer tubes 120 as well as a stranding disk 12 and a stranding nipple 13. The adhesive component 140 may be injected to the surface of the buffer tubes 120 at the position marked with the arrow 140. The adhesive component 140, for example, a hot melt adhesive, may be heated to a temperature between 60 to 120 when injected to the fixing areas.

[0043] FIG. 5B shows the injection nozzles 11a and 11b seen from a line marked in FIG. 5A with reference signs C-C. According to the embodiment shown in FIGS. 5A and 5B, two injection nozzles 11a and 11b are used to inject the adhesive component 140 in the fixing areas. In principle, one or more injection nozzles may be provided in the stranding and fixing apparatus 10.

[0044] According to the method of manufacturing described above, the usually used expensive yarns or tapes may be replaced by low-cost adhesive components, such as a low-cost glue of which only a small amount is used for injection to the reversal points of the stranded buffer tubes.

[0045] The complete sealing of the fixing areas by means of the adhesive component 140 allows to abstain from using expensive swelling yarns or water-swellable powders for blocking the propagation of water along the buffer tubes. The optical properties of the cable may be improved by reducing macro or micro bendings caused by swelling yarns which are usually located in any interstices of the cable core.

[0046] Furthermore, any problems caused by the quality of the yarns to fix the stranded buffer tubes around the strength member element, such as a break of the yarns, thick places, any fluff or any abrasion of the yarns, do not appear by using the adhesive component 140 for fixing the stranded buffer tubes. Furthermore, damage to the optical fibers caused by any indentations and any constrictions by the yarns are avoided.

[0047] Many modifications and other embodiments set forth herein will come to mind to one skilled in the art to which the embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the description and the claims are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. It is intended that embodiments cover the modifications and variations of the embodiments provided they come within the scope of the appended claims and their equivalents. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.