WO1997037263A1

WO1997037263A1 - An optical-fibre cable joint

Info

Publication number: WO1997037263A1
Application number: PCT/SE1997/000516
Authority: WO
Inventors: Peter Lo Curzio; Daniel Edman; Lennart Liden
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 1996-03-29
Filing date: 1997-03-25
Publication date: 1997-10-09
Also published as: AU2524897A; SE9601240L; SE507117C2; SE9601240D0

Abstract

The invention relates to a device for splicing one or more optical-fibre cables (1, 1'). When splicing optical fibres (2, 2'), for instance welding the fibres, it will preferably be possible to store fibre slack at the location of the splices without subjecting the optical fibres to mechanical forces. The inventive device includes a generally cylindrical body (4) having one or more grooves (8) disposed around the periphery of the cylindrical body. The grooves are adapted to accommodate one or more sleeves (6) that enclose an optical-fibre splice. The cylindrical body has at each end at least one recess for fastening the tension-relieving core (3) of the optical cables by means of a screw (5). The smallest permitted bending radius of the optical fibres determines the curved shape of the cylindrical body. The cylindrical body and the spliced optical fibres are enclosed by an outer casing (9). The invention also relates to a method of splicing optical-fibre cables.

Description

AN OPTICAL-FIBRE CABLE JOINT

FIELD OF INVENTION

The present invention relates to a method and to a device for splicing together one or more optical-fibre cables.

BACKGROUND ART

The splicing and branching of an optical-fibre cable requires the use of special devices to ensure satisfactory handling of the fibres, for instance to ensure that the optical-fibres are not bent excessively, are not pinched or subjected to load in any other way. It is particularly important that the optical-fibre is not curved to a radius that exceeds a specified smallest bending radius. Bending of an optical- fibre induces in the fibre stresses that have a negative effect on the useful life of the fibre, while excessive bending of the fibre will cause the light to be transmitted out of the fibre and result in undesired attenuation.

Splicing of optical-fibres also requires the ability to store optical-fibre slack in the splicing box. This is necessary primarily because welding equipment is often used to splice optical-fibres and because correct use of the equipment requires the presence of sufficient fibre slack in the splicing box. The ends of two optical-fibres to be spliced together are placed in the welding device and subsequent to splicing the fibres the spliced optical-fibre is coiled-up or folded in a controlled manner such as to ensure that the fibre will not be bent or curved excessively. Another reason for using fibre slack is because if welding is unsuccessful there must be sufficient optical-fibre to enable unsuccessful parts to be removed and the two cable ends re-spliced. In order to enable such repairs to be made, it is necessary to have access to the optical-fibre splices that must be remade. The aforementioned problems are overcome in present-day techniques with the use of a splicing box in which the optical-fibre is subjected to no load and in which fibre slack is stored in a manner such as to ensure that the smallest permitted bending radius will not be exceeded. The boxes contain variants of systems that use fibre cassettes in which fibre slack is wound up and in which a weld splice and its protective sleeve can be mounted. A plurality of cassettes are normally required when fibre cables that contain a large number of optical-fibres are to be spliced together, which results in large and expensive splicing boxes. Furthermore, a cable splice takes a relatively long time to make.

The same problems are, of course, encountered in mechanical splicing operations, e.g. with the use of optical contacts. Similar problems are also encountered when splicing optical- fibre ribbons as opposed to individual optical-fibres.

SUMMARY OF THE INVENTION

One problem with present-day solutions for splicing optical- fibre cables is that the cables consist of many different parts which, together, results in the need of a bulky and expensive splicing device. Furthermore, there is always the danger of an optical-fibre being curved or bent excessively prior to being placed into a cassette.

Accordingly, an object of the present invention is to provide a cheaper and simpler fibre splicing device in which fibre slack can be handled more easily and bending radii controlled more readily and with which it is ensured that the optical- fibre is subjected to no load.

In accordance with the invention, a cable splice is made with the aid of a cylindrical body having, for instance, two narrowing ends each of which includes one or a number of holes. Two optical-fibre cables are spliced together by first placing a tension-relieving core from each optical-fibre cable in a respective hole in the body and then securing the cores by means of a screw or like fastener. The cable splice is therewith relieved of tension by means of the cylindrical body. The optical-fibres in the cables are joined together to provide a fibre splice, which is protected by a sleeve. The cylindrical body includes a section that has one or more grooves. The width of each groove is adapted to the size of the sleeve and the grooves are used to fixate the sleeve and its fibre splice. When splicing the optical-fibres it is ensured that sufficient fibre slack is provided, and the slack is wound around the cylindrical body and the sleeve is then placed into an appropriate groove. The radius of the cylindrical body is determined so as to ensure that the bending radius of an optical-fibre will not be below the smallest permitted bending radius and consequently there will be very little danger of the fibre being damaged or deformed as it is wound around the body. The cylindrical body and its fibre splices can then be encapsulated and sealed in an outer casing.

The problem of producing a splice in which the smallest bending radius is ensured and the problem of correct handling of excess fibre and relieving the cable of tension forces at the same time is solved by means of the present invention in a simple and inexpensive manner. The splice is straight and compact and can also be placed within a tubular duct, for instance.

The invention will now be described in more detail with reference to preferred embodiments thereof and also with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a typical optical-fibre cable. Figure 2 illustrates an inventive splicing device.

Figure 3 illustrates an inventive splicing device on which a protective sleeve is fitted.

Figure 4a is a cross-sectional view taken on the line A-A in Figure 3.

Figure 4b is a cross-sectional view taken on the line B-B in Figure 3.

Figure 5 illustrates an alternative embodiment of the invention and shows both splicing and branching.

Figure 6a is a cross-sectional view taken on the line C-C in Figure 5.

Figure 6b is a cross-sectional view taken on the line D-D in Figure 5.

Figure 7 illustrates an alternative embodiment of a cylindrical body in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 is a perspective view of a typical optical-fibre cable 1 that includes a casing for protecting one or more embedded optical-fibres 2 against external forces. The optical-fibres may be placed singly or may be grouped in an optical ribbon. The optical-fibre cable may also include a tension-relieving element 3, which in the illustrated case is placed as a cylindrical core in the centre of the optical- fibre cable.

Figure 2 illustrates an inventive splicing device in which two optical-fibres cables 1, 1' are fitted, and shows the tension-relieving cores 3, 3' of the cables fastened to a cylindrical body 4 by means of a respective screw 5, 5' provided on a respective side of the body. It will be understood that the tension-relieving core may also be secured in some other way, for instance glued. Each optical- fibre cable includes one or more optical-fibres 2, 2' . In the illustrated case, these fibres are represented by two single fibres from each optical-fibre cable, for the sake of simplicity. An optical-fibre 2 from one optical-fibre cable 1 is spliced to an optical-fibre 2' from the other optical- fibre cable 1' and the splice protected by a sleeve 6. The splice, or join, may be a welded or mechanical splice, e.g. effected with the aid of so-called optical contacts in the latter case. The remaining optical-fibres are mutually joined in a similar way and protected by a sleeve that functions as a mechanical guard. The cylindrical body also includes a grooved section 7 that has one or more grooves 8. The grooves are adapted to the shape of the protective sleeves 6 and function to secure the sleeves. The grooves 8 preferably extend along the cylindrical body. The grooved section is located in the vicinity of the centre of the cylindrical body 4.

Figure 3 illustrates the same device as that illustrated in Figure 2 and shows the optical-fibres 2, 2' wound around the cylindrical body 4 and the protective sleeves 6 placed in appropriate grooves 8. The splicing device is placed inside a protective casing 9. The casing may have the form of a tube provided with connections at both ends, and may consist of two moulded halves or may be an integral moulded structure. In the latter case, the casing 9 surrounds the two optical- fibre cables 1, 1' and has bevelled edges 10. Appropriately labelled sleeves enable individual optical-fibres and splices to be easily identified.

Figure 4a is a cross-sectional view taken on the line A-A in Figure 3. The cross-section cuts through the cylindrical body 4 and the protective sleeve 9 at the attachment of the first optical-fibre cable 1. The tension-relieving core 3 of the optical-fibre cable is secured with the aid of a screw 5 and the two optical-fibres 2 lie around the cylindrical body 4. The optical-fibres need not lie in abutment with the cylindrical body 4, but may be located in the region between the cylindrical body 4 and the protective casing 9.

Figure 4b is a cross-sectional view taken on the line B-B in Figure 3. The cross-section cuts through the cylindrical body 4 and the protective casing 9 at the grooved section 7. A plurality of grooves 8 are disposed around the periphery of the cylindrical body so as to hold the protective sleeves 6 and their spliced optical-fibres 2 in place.

Figure 5 illustrates an alternative embodiment of an inventive splicing device, in which two optical-fibre cables 14, 15 are fastened to a first end of a cylindrical body 11 having partially planar sides and two optical-fibre cables 14', 15' are fastened to a second end of said body. In addition to splicing optical-fibres, this embodiment also enables optical-fibres to be branched. One optical-fibre 12 is spliced with an optical-fibre 12' , which are both wound around the body 11. The splice is protected by a sleeve 6 placed in a groove 8. This describes a splice in the absence of a branch. An optical-fibre 13 is spliced to an optical- fibre 13' and the optical-fibres are also wound around the body 11. The splice is similarly protected by a sleeve 6 and placed in a groove 8. This describes a splice that includes a branch, since the optical-fibres 12, 13 from the first end of the body arrive from different optical-fibre cables 14, 15, and since the optical-fibres 12', 13' from the other end of the body go into the same optical-fibre cable 14' . In other respects the splicing device is constructed in the same way as that described earlier with reference to Figure 3. Variants exist in which couplings between the different fibres can be achieved, so as to permit one optical-fibre 16 from one incoming optical-fibre cable 14 to be spliced with an optical-fibre 17 from the other incoming optical-fibre cable 15. Figure 6a is a cross-sectional view taken on the line C-C in Figure 5, in which the cylindrical body 11 has partially planar sides 23 and has four optical-fibres 12, 13, 16, 17 disposed therearound. The tension-relieving cores 18, 19 from respective incoming optical-fibre cables 14, 15 are secured by means of a respective groove 20, 21. The embodiment includes the externally mounted protective casing 22.

Figure 6b is a cross-sectional view taken on the line D-D in Figure 5 and shows the grooved section of the cylindrical body 11 having partially planar sides. The grooved section includes a plurality of grooves 8 in which the protective splice sleeves 6 are placed.

Figure 7 illustrates an alternative embodiment of a cylindrical body 24 of an inventive splicing device. The body is curved so that its ends point in one and the same direction. Each end 25 includes a recess 26 for accommodating an element that functions to relieve the tension in the cable and which is secured by means of a fastener device 27. The spliced optical-fibres and the splices are disposed around the curved cylindrical body, with the splices protected by a sleeve placed in a groove 28.

Because the cylindrical body of all of the aforedescribed embodiments has a smallest bending radius, the optical-fibre is unable to bend about a radius that is smaller than the radius of the cylinder. The cylinder body may, alternatively, be given a radius that is smaller than the smallest permitted bending radius of the optical-fibre, provided that the fibre is wound as a toroid around the cylindrical body. All embodiments include a grooved section disposed around the periphery of the cylindrical body, although this grooved section is not necessary with respect to the function of the device. However, the grooves in the grooved section simplify handling of the optical-fibres. It will be understood that the invention is not restricted to the aforedescribed and illustrated exemplifying embodiments thereof and that modifications can be made within the scope of the following Claims.

Claims

1. A method of splicing together optical-fibre cables which each include at least one optical-fibre and a tension- relieving element, characterized by - securing the tension-relieving element of each optical- fibre cable to a cylindrical body;

- splicing together the optical-fibres;

- placing the fibre splices around the cylindrical body; and

- encapsulating the cylindrical body and the fibre splices disposed thereon.

2. A method according to Claim 1, characterized by the additional steps of

- placing a sleeve around each optical-fibre splice;

- winding the fibres around the cylindrical body either completely or partially; and

- placing the spliced fibres and associated sleeve in a groove provided on the cylindrical body.

3. A device for splicing optical-fibre cables wherein each optical-fibre cable includes at least one optical-fibre and a tension-relieving element, characterized in that the device includes an essentially cylindrical body (4, 11) around which spliced optical-fibres (2, 2') are disposed; and in that the tension-relieving element {3, 3') of each of the fibre optic cables is fixed to the cylindrical body.

4. A device according to Claim 3, characterized in that the cylindrical body (4, 11) includes ends to which the tension- relieving elements (3, 3') of the optical-fibre cables are fastened.

5. A device according to any one of Claims 3 or 4, characterized in that the cylindrical body (4, 11) includes one or more recesses having fastener means for fastening the tension-relieving elements (3, 3' ) .

6. A device according to Claim 5, characterized in that the fastener means (5, 5') are screw fasteners.

7. A device according to any one of Claims 3-6, wherein the optical-fibre splices are protected by a sleeve, characterized in that the cylindrical body (4, 11) includes at least one grooved section (7) having one or more grooves (8) for accommodating one or more sleeves (6) .

8. A device according to Claim 7, characterized in that the grooved section (7) is located approximately midway on the cylindrical body (4, 11) with the grooves (8) disposed around the periphery of the body; and in that the grooves are essentially co-directional with the longitudinal axis of the body.

9. A device according to any one of Claims 3-8, characterized in that the cylindrical body (4, 11) is configured for a smallest bending radius of the spliced optical-fibres (2, 2') .

10. A device according to any one of Claims 3-9, characterized in that the cylindrical body (4, 11) and the optical-fibre splices (2, 2 ' ) are enclosed in a casing (9, 22) .