WO2008059212A1

WO2008059212A1 - Optical fibre breakout

Info

Publication number: WO2008059212A1
Application number: PCT/GB2007/004266
Authority: WO
Inventors: Geoffrey Martin Buddington; Darren Craig Atkinson
Original assignee: Tyco Electronics Uk Ltd
Priority date: 2006-11-17
Filing date: 2007-11-08
Publication date: 2008-05-22
Also published as: GB2455478B; GB0906832D0; GB0622968D0; GB2455478A

Abstract

An optical fibre cable breakout, wherein two or more optical fibres projecting from an optical cable sheath are separately enclosed in dual-walled protective tubes having longitudinal strength members, preferably synthetic fibre yarn, pre-installed between the dual walls of the tubes, and wherein a protective sleeve encloses the facing proximal ends of the cable sheath and the tubes.

Description

OPTICAL FIBRE BREAKOUT

This invention relates to an optical fibre cable breakout, wherein two or more optical fibres projecting from an optical cable sheath are separately enclosed in protective tubes with a protective sleeve enclosing the facing proximal ends of the cable sheath and the protective tubes.

A commercially known breakout of this kind involves a cable containing two optical fibres and a co-extending quantity of synthetic fibre yarn, usually Kevlar™ yarn, for longitudinal strength. A desired length of the cable jacket is removed and the thus-exposed lengths of the two optical fibres, each with approximately half of the longitudinal strength yarn, are respectively threaded through close-fitting protective tubes of plastics material. The protective tubes are positioned on the respective fibres with the proximal ends of the tubes sufficiently close to the proximal end of the cable sheath (from which the fibres are projecting), so that a heat-shrinkable protective plastics sleeve can be applied to enclose and secure the facing proximal ends of the sheath and tubes. Assembly of the known breakout can be hindered by the difficulty of threading each fibre and the co-extending strength yarn through its respective close-fitting tube. The finished breakout may furthermore be insufficiently robust for some practical purposes.

The present invention provides an improved optical fibre cable breakout, wherein two or more optical fibres projecting from an optical cable sheath are separately enclosed in dual- walled protective tubes having longitudinal strength members, preferably synthetic fibre yarn, pre-installed between dual walls of the tubes, and wherein a protective sleeve encloses the facing proximal ends of the cable sheath and the tubes.

The dual-walled tubes can be more robust than the simple tubes used in the aforementioned known breakout. It would of course be possible to provide breakouts in which the original strength yarn of the cable is threaded together with the respective optical fibres through the dual- walled protective tubes of the present invention. However, it is much preferred to thread the individual optical fibres alone through the dual-walled tubes, thus facilitating the threading process while deriving longitudinal strength from the strength members pre-installed between the dual tube walls.

Preferred embodiments of the breakouts according to this invention provide continuity of strength members from the cable sheath to the distal ends of the dual- wall protective tubes. For this purpose, it is preferred to strip off a suitable length of the outer wall of the tube, thus exposing the underlying length of the pre-installed strength member, and to make a physical connection between that exposed length of the tube strength member and the original cable strength member.

Such connection between the respective cable and tube strength members of synthetic fibre yarn could conceivably be made by simply knotting or fusion bonding them together. However, it is preferred to trim back the original cable strength member to a suitable length . and to form the connection by gripping the exposed portions of the respective cable and tube strength members by means of a suitable bridging member, preferably the aforementioned protective sleeve of the breakout according to this invention. For example, the trimmed exposed length (say 1.5 cm) of the original cable strength member may be folded back over the end of the cable sheath and gripped against the sheath by the overlying protective sleeve or other bridging member; while the exposed length (say 1 cm) of the dual-wall tube strength member may be similarly folded back and gripped against the outer tube wall, or may be gripped against the underlying untrimmed length of the inner tube wall, preferably after trimming of the exposed strength member to a length (say 5 to 7 mm) shorter than the exposed length of the inner tube.

While the above-indicated gripping of the respective cable and tube strength members might be achieved by applying a heat-shrinkable plastics sleeve of type known per se, a more robust connection is preferably provided by crimping a suitable crimp barrel, preferably a metallic crimp barrel, around the proximal end portions of the cable sheath and the protective tubes. Many well-known kinds of crimp barrel may be used, selection of suitable crimp barrels being a routine matter for those familiar with this field of technology.

The crimp barrel may be crimped directly onto the cable sheath to grip the folded-back ends of the cable strength member against the sheath. The crimp barrel could also be crimped directly onto the protective tubes to grip the exposed tube strength members against the inner and/or the outer tube walls, provided that care be taken to limit the crimp compression, for example by means of stop members on the crimping tool as known per se, in order to avoid damaging the enclosed optical fibres. However, a more robust connection is preferably provided by first securing the ends of the protective sleeves and their pre-installed strength members in a substantially rigid sub-sleeve, hereinafter referred to as a "tube head", dimensioned to fit at least partly within the crimp barrel, so that the crimp barrel can be more reliably crimped onto this tube head without undue risk of damage to the enclosed optical fibres. The tubes and strength members are secured in the tube head by any convenient means, preferably by adhesive or resin, especially a curable adhesive/resin formulation, for example epoxy or polyurethane. Suitable tube heads can be made of any sufficiently rigid material, preferably metal, and may have any desired shape, preferably a round body tapering to an oval port. The tube head can be made by extruding and drawing a metal tube using known techniques. Suitable tube heads can be obtained from Tyco Electronics.

The tubes are preferably arranged so that the exposed ends of their inner walls project through the tube head ready to subsequently receive the optical fibres. The head with the dual-wall tubes and strength members secured therein can then receive the fibres and be slid along the fibres and into the end of the crimp barrel. The barrel can then be crimped onto the tube head either before or after the other end of the barrel is crimped onto the cable sheath.

The materials and manufacture of the components forming the cable breakouts according to this invention are not critical and suitable examples are known per se and readily obtainable from sources known to those skilled in the relevant field of technology. The dual- walled protective tubes can be made by laying the strength members along the exterior of a first tube and extruding a second tube over the first tube and strength members. Flexible plastics materials are preferred for both tubes, especially low-smoke and/or low-halogen plastics formulations. Suitable dual-walled tubes with strength members can be purchased from various suppliers known to the trade.

A specific embodiment of this invention as applied to a two-fibre optical cable of known type will now be described by way of non-limiting example, with reference to the accompanying drawings. It will be understood that breakouts from cables carrying more than two fibres, for example three or four fibres, could be made analogously and are included in the invention, but two-fibre breakouts are especially desirable for use in transmit/receive telecommunications cabling systems, for example in patchcords used by British Telecom. The ruggedised breakouts according to the present invention are advantageous for use in physically demanding enviroments.

In the drawings :-

Figure IA shows schematically a partly-assembled breakout of the previously known kind using a heat-shrinkable sleeve;

Figure IB shows the known breakout of Fig. IA after completion;

Figure 2 shows schematically the dual-walled protective tubes installed in a tube head according to the present invention; Figure 3A shows schematically a partly-assembled breakout according to the present invention using the tube and head assembly of Figure 2; and

Figure 3 B shows schematically the breakout of Fig. 3 A after completion.

Referring to the drawings, Figure IA shows a schematic version of the aforementioned previously known breakout, comprising a two-fibre optical cable of known kind, for example a COMACC ™ Limited Fire Hazard Optical Fibre Cable, whose sheath has been removed to reveal a length of its two optical fibres 11 and a corresponding length of its cable strength member 12 of Kevlar ™ yarn, roughly equal portions of which have been arranged to lie respectively along the two optical fibres 11. Each of the optical fibres 11 and its associated portion of the cable strength member 12 has been threaded through a simple protective tube 13 of plastics material (shown as transparent for illustrative purposes, but usually opaque in practice), for example a low-smoke, low-halogen polyolefm formulation sleeted from the many such materials known per se. A heat-shrinkable plastics sleeve 14 (shown as transparent for illustrative purposes, but usually opaque in practice), for example the low- shrink-temperature sleeves available from Tyco Electronics under the trade marks RAYCHEM ATUM 6/2, is positioned around the assembly. The protective tubes 13 and heat-shrinkable sleeve 14 are subsequently slid along the optical fibres in the direction of the arrows A so that the sleeve 14 overlaps the proximal end 15 of the cable sheath and the proximal ends 16 of the protective tubes. The sheath 14 is subsequently heat-shrunk around the assembly, by hot air or infra-red heating as known per se, to reach the completed breakout shown in Figure IB securing together the cable 10, the protective tubes 13, and the optical fibres 11 together with their co-extending portions of the strength member 12 (shortened for clarity in this view).

Figure 2 shows schematically the dual-walled protective tubes 20 (shown as transparent for illustrative purposes, but usually opaque in practice) according to the present invention, each having an inner tube 21 and an outer tube 22, with strength members 23 pre- installed between the inner and outer tube walls. In this example, the inner and outer tubes are extruded from low-smoke zero-halogen plastics material as known per se, and the strength members pre-installed between the tube walls are Kevlar yarns, also as known per se, which are laid along the inner tube then covered by extrusion of the outer tube onto the inner tube/yarn assembly. The outer tubes 22 as shown have been cut back to expose a length (for example 10 mm) of the inner tubes 21, and the correspondingly exposed length of the pre- installed strength members 23 has been trimmed to a length (for example 5-7 mm) shorter than the exposed length of the inner tube wall. The dual-walled tubes are positioned in a metallic tube head 24 (shown as transparent for illustrative purposes, but opaque in practice), which encloses the proximal ends of the outer tubes 22 and the trimmed ends of the strength members 23, but allows the open ends of the inner tubes 21 to project through the head 24. The head in this example is supplied in connector kits available from Tyco Electronics under the trade mark AMP. The head is then filled with two-part curable epoxy adhesive of known kind (omitted from the drawing for clarity), which is cured to secure the tubes and strength members within the head 24.

Figure 3A shows the tube head 24 and the secured dual-walled tubes 20, as illustrated in Figure 2, partly assembled to form a breakout according to the present invention. The aforementioned optical fibre cable 10 now has its strength member yarn 12 trimmed and folded back over the cable sheath, thus exposing the two optical fibres 11 separately from the strength member. The exposed lengths of the optical fibres 11 have been relatively easily threaded through the close-fitting inner tubes 21 of the dual- walled protective tubes 20, and a metal crimp barrel 30 of suitable sized is positioned ready for movement in the direction of arrow A to overlap the end of the cable 10 and the trimmed length of cable strength member 12. The tube head 24 and conjoined protective tubes 20 are ready for sliding along the optical fibres 11, also in the direction of arrow A, to position the head 24 at least partly within the crimp barrel 30. This may be done before or after the aforesaid movement of the crimp barrel to overlap the cable end.

Figure 3 B shows schematically the resulting ruggedised breakout according to the present invention, wherein the crimp barrel 30 has been crimped at point 31 to secure the barrel and the underlying trimmed length of cable strength member 12 against the sheath of the cable 10, and has been crimped at point 32 to secure the barrel to the tube head 24. The crimped barrel 30 thus robustly secures the protective tubes 20 and their pre-installed strength members to the cable 10 to protect the optical fibres and to resist logitudinal pulling stresses which may be encountered in practical use.

Claims

CLAIMS:

1. An optical fibre cable breakout, wherein two or more optical fibres projecting from an optical cable sheath are separately enclosed in dual-walled protective tubes having longitudinal strength members, preferably synthetic fibre yarn, pre-installed between the dual walls of the tubes, and wherein a protective sleeve encloses the facing proximal ends of the cable sheath and the tubes.

2. A breakout according to claim 1, wherein a strength member of the cable is threaded together with the respective optical fibres through the inner tube of the dual- walled tubes.

3. A breakout according to claim 1, wherein the individual optical fibres alone are threaded through the inner tube of the dual- walled tubes.

4. A breakout according to any preceding claim, wherein continuity of strength members from the cable sheath to the distal ends of the dual-wall protective tubes is provided.

5. A breakout according to claim 4, wherein the continuity is provided by stripping off a suitable length of the outer wall of the dual- walled tube, thus exposing the underlying length of the pre-installed strength member, and making a physical connection between that exposed length of the tube strength member and the original cable strength member.

6. A breakout according to claim 5, wherein the connection between the respective cable and tube strength members of synthetic fibre yarn is made by knotting or fusion bonding them together.

7. A breakout according to claim 5, wherein the connection between the respective cable and tube strength members is made by trimming back the original cable strength member to a suitable length and securing the exposed portions of the respective cable and tube strength members by means of a suitable bridging member, preferably the aforementioned protective sleeve.

8. A breakout according to claim 7, wherein the trimmed exposed length of the original cable strength member is folded back over the end of the cable sheath and secured against the sheath by the overlying protective sleeve or other bridging member.

9. A breakout according to claim 7 or 8, wherein the exposed length of the dual-wall tube strength member is folded back and secured against the outer tube wall; or is secured against the underlying untrimmed length of the inner tube wall, preferably after trimming of the exposed strength member to a length shorter than the exposed length of the inner tube.

10. A breakout according to claim 5, wherein the connection between the respective cable and tube strength members is made by crimping a suitable crimp barrel, preferably a metallic crimp barrel, around the proximal end portions of the cable sheath and the protective tubes.

11. A breakout according to claim 10, wherein the crimp barrel is crimped directly onto the cable sheath to grip the folded-back ends of the cable strength member against the sheath.

12. A breakout according to claim 10 or 11, wherein the crimp barrel is crimped directly onto the protective tubes to grip the exposed tube strength members against the inner and/or the outer tube walls.

13. A breakout according to claim 10 or 11, wherein the ends of the protective sleeves and their pre-installed strength members are secured in a substantially rigid sub-sleeve ("tube head") dimensioned to fit at least partly within the crimp barrel, and the crimp barrel is crimped onto this tube head.

14. A breakout according to claim 13, wherein the tubes and strength members are secured in the tube head by means of adhesive or resin, preferably epoxy or polyurethane or another curable adhesive or resin formulation.

15. A breakout according to claim 13 or 14, wherein the tubes are preferably arranged so that the exposed ends of their inner walls project through the tube head and receive the optical fibres.