GB2317238A

GB2317238A - Manifold device for terminating optic fibre cable

Info

Publication number: GB2317238A
Application number: GB9619274A
Authority: GB
Inventors: Raymond Charles Foss; Andrew Stephen Cammack
Original assignee: Bowthorpe PLC
Current assignee: Bowthorpe PLC
Priority date: 1996-09-16
Filing date: 1996-09-16
Publication date: 1998-03-18
Anticipated expiration: 2016-09-16
Also published as: GB9619274D0; GB2317238B

Abstract

A manifold device 20 for fitting to a prepared end of a slotted-core optical fibre cable comprises a forward portion of enlarged internal diameter for fitting over a bare length of slotted-core 10 of the cable, and a rearward portion of reduced internal diameter for fitting over an axial reinforcing member 12 of the cable. The tubular body is formed with slots 22a at its forward end through which optical fibres 14 of the cable pass. The slots 22a co-extend with grooves 22 on the outer surface of the rearward portion of the body, the grooves 22 being arranged to receive the ends of protective sleeves (30, Fig 4) which are slid onto the exposed optical fibres 14. Teeth (24, Fig 3) are provided inside the device 20 to prevent it from turning around the axis of the cable, once applied. The manifold device 20 serves to provide means for protecting and holding optical fibres at the point where they emerge from the cable.

Description

Manifold device for optical fibre cables The present invention relates to a manifold device for use on "slotted core" optical fibre cables when coupling these to enclosures which store fibres and/or fibre splices.

Slotted core optical fibre cables comprise a core member formed with a series of parallel grooves which follow a helical path (which usually alternates direction periodically), each groove receiving one or more optical fibres: several fibres in each groove may be connected together as a ribbon. The core member and its fibres are enclosed within an outer sheath.

When such a cable is coupled to a terminal or jointing unit, the sheath and core member are cut back over selected lengths, to bare the optical fibres. The fibres must then be laid carefully in the storage trays etc of the terminal or jointing unit, where typically some or all of the fibres are spliced to the fibres of other cables. It is important that the bare lengths of the fibres should be properly supported and protected: it has been proposed to fit a manifold device to the cut-back end of the cable, and lay the fibres into grooves or guideways of this manifold device. However, such manifold devices which have been proposed hitherto suffer the drawback that they are not sufficiently securely positioned, and in particular are liable to twist around the axis of the cable, with the risk that this may cause the fibres to be stressed or to break, where they pass from the cable core to the manifold device.

We have now devised a manifold device which overcomes the problem outlined above.

In accordance with the present invention, there is provided a manifold device for fitting to a prepared end of a slotted-core optical fibre cable, the manifold device comprising a tubular body having a forward portion of enlarged internal diameter for fitting over a bare length of core of the cable, and a rearward portion of reduced internal diameter for fitting over an axial reinforcing member of the cable, the tubular body being formed with slots at its forward end for accommodating optical fibres of the cable, and being formed with projecting teeth for engaging the fibre-containing grooves of the cable core member.

The latter teeth act to prevent the manifold device, once applied, turning around the axis of the cable. Preferably a spring washer is applied as a push-fit over the reinforcing member of the cable, to abut the rearward end of the manifold device and hold it axially in position.

Preferably the tubular body of the manifold device is formed with a plurality of longitudinally-extending grooves on its outer surface, into which the optical fibres from the cable are located. Preferably the optical fibres are passed through protective sleeves, the end portions of these sleeves being engaged as a push-fit into respective grooves of the manifold device.

Preferably the teeth of the manifold device, which engages respective grooves of the cable core element, are provided on an annular shoulder formed internally between the forward and rearward portions of the device.

Preferably the forward portion of the manifold device comprises a plurality of longitudinally-projecting fingers with gaps between them, providing the aforementioned slots through which the fibres from the cable pass.

It will be appreciated that a free end of a slotted core cable can be prepared to receive the manifold device.

Equally however, the cable can be appropriately prepared at any desired point intermediate its opposite ends, by removing a length of sheath, then a shorter length of core member, and a still shorter length of the axial reinforcing member. A manifold device is then applied to each of the two cut-back ends of this zone.

Preferably the manifold device is provided with a separate tubular cover which fits over it.

The tubular cover is preferably longitudinally-split so that it can be applied around the manifold device, rather than having to be slid on from its rearward end.

An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings in which: FIGURE 1 is a view of an end portion of a slotted-core optical fibre cable, prepared ready to receive a manifold device in accordance with the invention; FIGURE 2 is a side view of a manifold device in accordance with the invention being applied to the cable end; FIGURE 3 is a sectional view of the cable end with the manifold device applied to it; FIGURE 4 is a similar view of the cable end and manifold device, showing the use of protective sleeves for the bare optical fibres; FIGURE 5 is a view a loop of cable which has been prepared to receive a manifold device on each of its cut-back ends; and FIGURE 6 is a view similar to Figure 5, showing protective covers applied to the manifold devices.

Referring to Figure 1, there is shown an end portion of a slotted core cable, prepared for coupling to a terminal or jointing unit. The cable comprises a cylindrical core member 10 through which an axial reinforcing member 12 extends. The core member 10 is formed with a plurality of grooves 11 which follow parallel helical paths on the outer surface of the core member: typically, the direction, or sense in which the helical path runs, alternates at intervals along the length of the core member 10. A number of optical fibres 14 are housed within each groove 11: the fibres of each groove may be loose or they may be joined together to form a ribbon. The core member 10 and its fibres 14 are enclosed within an outer sheath 15.

Figure 1 shows the sheath 15 of the cable cut back for a certain distance, and the core member 10 cut back for a shorter distance, to leave a length of approximately 180mm of the reinforcing member 12 bare, and a length of 23mm of the core member 10 bare. The optical fibres 14 are accordingly free to fan out from their grooves, from the cut-back end of the sheath 15.

Figure 2 and 3 shows a manifold device 20 in accordance with the invention, being applied to the end of a cable once prepared as shown in Figure 1, and Figure 3 shows the manifold device once applied to the cable. The manifold device 20 comprises a tubular body which has a forward portion of enlarged internal diameter, and a rearward portion of reduced internal diameter. The forward portion is a sliding fit over the core member 10 of the cable and the rearward portion is a sliding fit on the reinforcing member 12 of the cable. The manifold device is formed with a number of longitudinallyextending grooves 22 which extend, in the radial direction, entirely through the wall of the forward portion of the tubular body 20, thus defining a plurality of forwardly-projecting fingers 23 separated by through-slots 22a.

The manifold device is slid onto the cable until (as shown in Figure 3) its forward end (i.e. the free ends of the fingers 23) abuts the cut-back end of the cable sheath 15: at the same time, an internal shoulder between the forward and rearward portions of the manifold device abuts the cut-back end of the core member 10 of the cable. Further, that internal shoulder, between the forward and rearward portions of the manifold device, is formed with a plurality of forwardlyprojecting teeth 24, which fit into the ends of respective grooves 11 of the cable core member 10: the manifold device is accordingly prevented from turning around the axis of the cable.

Once the manifold device has been applied to the cable, as just described, a spring washer 26, of the type having a star-shaped central aperture, is slid as a push-fit along the reinforcing member 12, to abut the rearward end of the manifold device. In conventional manner, the spring washer 26 resists movement in the opposite direction, and so holds the manifold device 20 firmly in abutment with the cut-back ends of the cable sheath and cable core member.

Care is taken, when applying the manifold device, to ensure that the optical fibres locate within the through-slots 22a: advantageously, and as shown, the through-slots 22a widen towards the forward end of the device.

Referring to Figure 4, the fibres 14 are next passed through protective sleeves 30. An end portion of each sleeve 30 is inserted, as a push-fit, into a groove 22 of the manifold device, adjacent its rearward end, leaving a shore bare length 14a of the optical fibre or fibres within the corresponding through-slot 22a of the device. The protective sleeves, and the optical fibres which they carry, are fed to trays or cassettes within the terminal or jointing unit, for storage of the fibres and/or their splices to further cables.

Referring to Figure 5, in some cases it is necessary to bare a length of cable to provide bare fibre loops, for arrangement in storage trays or cassettes. In these cases, a length of the cable sheath is removed, then a shorter length of the cable core member 10, and finally a still shorter length of the reinforcing member 12: at each end of this zone, a predetermined length of the core member 10 projects from the cut-back end of the sheath, and the reinforcing member 12 projects from the cut-back end of the core member. A manifold device 20 is then fitted to each cut-back end of sheath and core member, in the same manner as previously described.

In all cases, a tubular cover may be applied over the manifold device. Such covers are shown at 40 in Figure 6, applied to the two manifold devices of the arrangement shown in Figure 6. In this case, each tubular cover 40 is longitudinally split, so that it can be applied around the manifold device. The cover 40 has additional slits, commencing at its rearward end and extending part-way along its length, through which protective sleeves 30 extend, these sleeves carrying fibres of the cable which have been cut.

The fibres which remain uncut are enclosed within a sleeve 32. This sleeve is split from end-to-end (along a helical line of relatively large pitch) to enable it to be applied to its fibres. The sleeve 32 is applied before the tubular covers 40, and the latter covers are applied so that the rearward ends of the covers embrace the ends of the sleeve 32.

Claims

1) A manifold device for fitting to a prepared end of a slotted-core optical fibre cable, the manifold device comprising a tubular body having a forward portion of enlarged internal diameter for fitting over a bare length of core of the cable, and a rearward portion of reduced internal diameter for fitting over an axial reinforcing member of the cable, the tubular body being formed with slots at its forward end for accommodating optical fibres of the cable, and being formed with projecting teeth for engaging the fibre-containing grooves of the cable core member.

2) A manifold device as claimed in claim 1, in which the tubular body of the manifold device is formed with a plurality of longitudinally extending grooves on its outer surface.

3) A manifold device as claimed in claims 1 or 2, in which the teeth are provided on an annular shoulder formed internally between the forward and rearward portion of the device.

4) A manifold device as claimed in any preceding claim, in which the forward portion of the manifold device comprises a plurality of longitudinally-projecting fingers with gaps therebetween, providing said slots through which the fibres from the cable pass.

5) A manifold device as claimed in any preceding claim, comprising a separate tubular cover.

6) A manifold device as claimed in claim 5, in which the cover is longitudinally-split.

7) A manifold device substantially as herein described with reference to the accompanying drawings.