FIBRE OPTIC SPLICE CLOSURE

Abstract: A closure assembly for encapsulating splices between optical fibres of one or more fibre optic cables, the assembly comprising first and second hollow cover portions having mating surfaces which can be sealed together around the fibre optic cable(s), wherein one or both of the cover portions is provided with splice retaining means for securing the said optical fibre splices.

Description: FIBRE OPTIC SPLICE CLOSURE This invention relates to a closure assembly for a splice in one or more fibre optic cables. A fibre optic cable typically comprises a plurality of optical fibres contained within a protective outer sheath, usually with an intermediate mechanical protection layer between the fibres and outer sheath to prevent breakage of the fibres during installation or use of the cable. Where it is desired to make a splice to one or more of the optical fibres of the cable, it is necessary to remove the outer sheath and mechanical protection layer to access the fibre or fibres to be spliced. The resultant exposed optical fibres need to be protected not only against the environment, but also against overbending which could break the fibres or result in signal attenuation. Fibre optic splice closures must therefore be designed to satisfy these needs. Known fibre optic splice closures typically comprise a hollow enclosure containing one or more protective splice trays. The splice trays store the optical fibre splices, and may also store any uninterrupted, but exposed optical fibres. For example, in a branch splice, the splice tray may store not only the optical fibre splices but also those fibres bared of outer cable sheath, which have not themselves been spliced. Where the outer cable sheath is removed to make a splice to optical fibres of a fibre optic cable using a splice closure, it is usual to include within the closure an excess length of bared fibres, both of the spliced fibres, and any uninterrupted fibres. This is to provide for future splicing or other rearrangements to the network. This excess fibre is usually formed into one or more loops and stored in the splice tray in a looped configuration. US 4805979 (Minnesota Mining and Manufacturing Corp) describes a typical known fibre optic splice closure. It comprises a base and a cover which are both in the form of half shells having mating surfaces secured together by bolts. Fixed to the base of the splice closure is one or more splice trays, comprising splice receiving channels extending along the tray, and fibre retaining lips extending around at least part of the edge of the tray. According to US 4805979, where a branch splice is made, the fibres to be joined are spliced and placed in the splice receiving channels of the splice tray, and the fibres which are not to be spliced, together with excess length of the spliced fibres, are coiled and placed beneath the fibre retaining lips around the periphery of the tray. EP-A-0159857 (Raychem) describes a fibre optic splice closure comprising a base through which cables pass, and a dome shaped closure which fits onto the base. Within the closure are provided a plurality of hinged splice trays for holding the optical fibre splices. The closure is efficient and effective for enclosing a large number of splices, but is somewhat bulky. We have discovered that it is possible to make a particularly compact and useful splice closure by incorporating the function of the splice tray in the cover portions forming the closure of the fibre optic splice. That is, one or more outer cover portions (i.e. parts of the outer housing itself of the splice closure) may comprise a splice storage tray. Thus the present invention provides a closure assembly for encapsulating splices between optical fibres of one or more fibre optic cables, the assembly comprising first and second hollow cover portions having mating surfaces which can be sealed together around the fibre optic cable(s), wherein one or both of the first and second cover portions is provided with splice retaining means for securing the said optical fibre splices. According to the present invention, therefore, one or both of the cover portions is adapted not only to carry out the function of a cover, but also to act as a splice tray. Since the splice tray function and the enclosure cover function are provided by the same part, the cost of providing separate parts is avoided. Furthermore the resulting enclosure is compact. In this specification, the expression "loose optical fibres" refers to the excess lengths of the spliced optical fibres and/or lengths of unspliced optical fibres (sometimes referred to as " express" optical fibres) which are typically included in a fibre optic splice closure. The excess lengths of the spliced fibres are a result of the need to provide sufficient lengths of the fibres in order to carry out the splicing (e.g. fusion splicing) operations, and also in order to provide for future re-splicing etc. Furthermore, unspliced express fibres which are stored in the closure may need to be cut and spliced in the figure. The "loose optical fibres" are preferably contained in tubes, and these tubes are sometimes referred to as "loose tubes" (hence the expression "loose fibres"). In one embodiment of the invention, only one of the first and second cover portions is adapted to be a splice tray for securing the optical fibre splices. Preferably, in this embodiment, the other cover portion is adapted to be a storage tray for storing lengths of loose optical fibres. The other cover portion is adapted to be a storage tray by being provided with loose fibre retaining means, e.g. in the shape of lips or projections. In another embodiment both of the first and second cover portions are adapted to be splice trays for securing the optical fibre splices. To this end, both the cover portions are provided with splice retaining means. In this embodiment, an additional fibre storage tray is preferably provided for storing any lengths of loose optical fibre, the additional tray being provided with loose fibre retaining means. In addition to being provided with splice retaining means (and thereby being adapted to be splice trays), the first and/or second cover portion may also be provided with loose fibre retaining means (and thereby be adapted to be a storage tray). Conveniently, for example, a cover portion which is adapted to be both a splice tray and a storage tray may store any excess length of the spliced fibres, while storage of unspliced fibres (sometimes also known as "express" fibres) may be accommodated in either the other cover portion, or in an additional, separate storage tray. The cover portions are hollow and have mating surfaces which can be sealed together around the fibre optic cables. Preferably the cover portions are generally similar in shape. In a preferred embodiment, one or each cover portion is generally elongate, having a substantially flat major surface and side walls extending inwardly from the elongate edges of the flat major surface. In preferred embodiments the or each cover portion is tapered at one or each of its ends. This arrangement may enhance sealing to the cables. The splice retaining means in the cover portion(s) to adapt it/them to be a splice tray may take any convenient form. Suitable means would be apparent to the man skilled in the art. In one embodiment according to the present invention, the cover portion is provided with two upstanding flanges which extend substantially parallel to each other along at least part of their length. Resilient material, for example foam, may be provided between the upstanding flanges, into which, in use, the fibre splices are positioned in order to secure them. The resilient material is preferably positioned in a channel shape between the flanges. The separation of the upstanding flanges, and the thickness of the foam, or other resilient material are selected according to the size of the splices so that the resilient material must be compressed slightly in order to insert the splices. This makes it easy for the installer to insert the splices, while retaining them securely in place during service life. The parallel upstanding flanges may be curved or straight, according to what is desired for optimum splice securement. One of the parallel upstanding flanges may be provided by part of the wall of a cover portion. Each cover portion which is adapted to be a splice tray, may be provided with one or more pairs of parallel upstanding flanges in order to accommodate fibre splices. Where one or each cover portion is also adapted to be a storage tray, or where an additional storage tray is provided, the storage function is preferably provided by lips or projections extending so as to be able to support loose fibre. The lips or projections are loose fibre retaining means. The lips or projections are preferably arranged to support the loose fibre in a looped configuration. This minimises the possibility of damage to the fibres, or attenuation of signal, both of which could result from overbending of the fibres. The cover portions may be secured to each other by any suitable means. For convenience of handling, the cover portions are preferably pivotally connected, e.g. hinged together. For the preferred embodiment of generally elongate cover portions, the cover portions are preferably pivotally connected along one longitudinal edge. A pivotal connection means that the two cover portions are held together, and therefore handled as one piece, but allows the cover portions to be opened up completely, e.g. onto a flat surface, allowing easy access to the splice tray region and storage tray region. Where a separate storage tray is provided, in addition to the two cover portions, the separate storage tray is preferably also pivotally connected, e.g. hinged, to the two cover portions. The pivotal connection is preferably such that the two cover portions can be laid out onto a substantially flat surface, and the additional storage tray projects upwards (or downwards) therefrom. The additional storage tray is preferably able to rest in a position substantially perpendicularly to the laid out cover portions. This makes it easy for an installer to access, and work on, the inside of each cover portion and the additional storage tray. This pivotal connection arrangement is preferably provided by a connection plate on which the storage tray is mounted. The connection plate is preferably provided with both pivoting means and sliding means. The pivoting means allow the storage tray to pivot relative to each cover portion, and the sliding means allow the storage tray to slide transversely relative to each cover portion, at least when the storage tray has been pivoted into an orientation when it is substantially parallel to the said cover portion. The sliding mechanism allows the cover portions to move towards each other in order to close the assembly. The pivoting and sliding design provides a splice closure which is compact and easy to handle because it is in one piece, but also one which allows full and easy access to the splice tray and storage tray regions. The preferred pivoting (e.g. hinge) arrangement secures the preferred elongate cover portions along one edge. Securement along the other edge may be provided by any suitable means. As an example the cover portions may be provided with mating projections which snap fit together. Preferably the securement means are such as to allow easy reopening for later work on the splice closure. The closure assembly according to the present invention may be shaped to enclose any type of splice, e.g. an in-line splice, a butt splice, or a branch splice. In preferred embodiments, cables project, therefore, from one or both ends of the splice closure. In addition to securing the cover portions to each other, the cover portions must be sealed to each other. This may be done in a number of ways, as would be apparent to the man skilled in the art. In a preferred embodiment according to the invention, the mating surfaces of the first and second cover portions are respectively tongue and grooved shaped, and provided with a strip of sealing material within the tongue and groove. This sealing material may, for example, be a rubbe, a gel, a polymeric foam or a combination thereof. Furthermore, there is preferably a seal around the cables where they enter the closure, which may also be rubber, gel, polymeric foam etc. Where a gel is used, it is preferably a thermoplastic gel. A preferred polymeric foam is silicone rubber foam. Although the cover portions are preferably connected, e.g. pivotally, to each other for ease of handling, this connection is preferably detachable. This makes it possible to provide interchangeable cover portions, which can be selected according to the closure assembly desired for a particular operation. For example cover portions may be provided adapted to be classic in-line splice trays, tap-off trays, storage trays, etc. Thus, a second aspect of the invention provides a kit of parts comprising three or more cover portions, any two of which may be used together for forming a closure assembly for optical fibre splices, each cover portion being provided with a mating surface to seal to another of the cover portions, and being adapted to provide different functions in the closure assembly. Preferably at least one cover portion in the kit of parts is adapted to be a splice tray. A third aspect of the invention provides a method of encapsulating splices between optical fibres of one or more fibre optic cables using a closure assembly according to the first aspect of the invention, the method comprising: (i) splicing optical fibres and securing them in the splice retaining means of the or each cover portion, and; (ii) sealing the mating surfaces of the cover portions to each other. The closure assembly of the present invention is compact and easy to use. Nonetheless it may easily be used to enclose up to about 24 splices, or more. Embodiments of the invention will now be described, by way of example, in which: Figures 1, 2 and 3 are each perspective views showing three different embodiments of closure assembly according to the invention, each in an open configuration; Figure 4 is a cross sectional view through the optical fibre splice retaining region of each of Figures 1 to 3, taken along the line IV - IV of each of Figures 1 to 3; Figure 5 shows the closed configuration of each of the closure assemblies of Figures 1 to 3; Figures 6a and 6b are schematic cross-sectional views showing the assembly of the main component parts of the closure assembly of Figure 2; Figures 7a, 7b, and 7c are schematic cross-sectional views showing the assembled assembly of Figure 6 in closed, partially opened, and fully opened configuration respectively; Figures 8a and 8b are schematic perspective views of part of the main component parts of the closure assembly of Figure 2, showing assembly of those component parts; and Figures 9a, 9b and 9c are schematic perspective views showing part of the assembled closure assembly of Figure 8 in closed, partially open, and fully open configurations respectively. Referring now to the drawings, Figure 1 shows a first embodiment of closure assembly according to the present invention, comprising first and second cover portions 2,4 in the form of half shells. The cover portions 2 and 4 have mating surfaces 6 which can be sealed to each other. The manner in which sealing of mating surfaces 6 is carried out is described later. Each cover portion 2,4 is generally elongate and has a substantially flat major surface (not visible in the figure) and side walls 8 extending inwardly from the major surface to the said mating surfaces 6. Cover portion 2 is provided with a pair of parallel elongate, straight, upstanding flanges 10 containing a channel of resilient foam 12 between them. The fibre optic splices 14 are positioned between the upstanding flanges 10,10' and the resilient foam 12 secures the splices firmly in place. The upstanding flanges 10, 10' in combination with the foam 12 therefore provides splice retaining means in the cover portion 2. The securement of the splices by the foam 12 and flanges 10, 10' is described in more detail with reference to Figure 4. In the embodiment shown in Figure 1, one of the upstanding flanges 10' is provided by part of the side wall 8 of the cover portion 2. Cover portion 2 is also provided with lips or projections 16, 18 which store loops of lengths of fibre 20 en-route to the splice region. Cover portion 4 in contrast is not provided with splice retaining means. Instead it is provided with projections 22 which act as loose fibre storage means. The projections 22 hold loops of excess lengths of fibre which are advantageously retained in the splice closure for future rearrangements. Lengths of excess fibre of the spliced fibres may be held in cover portion 4, and/or also lengths of excess unspliced fibre, or so-called "express" fibre. Figure 1 is an in-line splice and two fibre optic cables enter the closure from each end. The cover portion 4 is provided with a sealing material 26, e.g. a gel or rubber to seal around the cables 24. The sealing material 26 contains channels to receive the cables 24. In addition, retaining strips 28 are wrapped around the cables to grip the cables and secure them to the cover portions of the closure. The retaining strips 28 also serve to retain the sealing material 26 in place (which is particularly useful when the sealing material is gel). Within the splice closure the outer sheath of the fibre optical cable is removed, and lengths of optical fibre exposed. Loops of excess fibre are organised in the storage region provided by cover portion 4, and the fibres to be spliced are led into cover portion 2, and the splices arranged as described above. Once splicing operations are complete the cover portions 2 and 4 can be brought so that mating surfaces 6 are sealed together to close the closure. The closed closure is shown later as Figure 5. The cover portions 2 and 4 are provided with hinges 30 which allow the cover portions 2 and 4 to be opened and laid flat for easy access. Thus the embodiment of Figure 1 provides a splice closure for an in-line splice where one half shell cover portion 2 is the splice tray, and the other half shell cover portion 4 is the storage tray. The storage tray organisation is on the same plane as the plane of entry of the cables which is simple and avoids cable or fibre over bending. The overall design is compact and easy to use. Figure 2 shows another embodiment of splice closure according to the invention. Like reference numerals are used to refer to like parts as compared to Figure 1. In this embodiment both the cover portions 2 and 4 are provided with splice retaining means 10,12 (not visible in cover portion 4), and a separate storage tray 32 is provided for storing excess length of loose optical fibre. As in Figure 1 the cables 24 enter the closure in the plane of the organising storage tray, which in the embodiment of Figure 2 is the additional tray 32, and in the embodiment of Figure 1 was the cover portion 4. The cover portions 2 and 4 and the additional tray 32 are hinged at 30 in a manner allowing the cover portions 2 and 4 to be laid out flat, while the additional storage tray 32 projects perpendicular thereto. This hinging mechanism is described in more detail later. The embodiment of Figure 2, as Figure 1 is a two cable in, two cable out, in-line splice. Figure 3 describes another embodiment of splice closure according to the invention. Again, like reference numerals are used to refer to like parts compared to Figures 1 and 2. The splice closure of Figure 3 is for a branch joint, and it joins fibres from a straight main cable 34 to those from two branch cables 36. As before the cover portion 2 acts as a splice tray. The cables enter the closure in the plane of the cover portion 4. In this embodiment the main cable passes straight through (with fibres tapped of for splicing to the branch cables), and there are no loops of excess fibre stored in the cover portion 4. Figure 4 is a cross-sectional view taken along the line IV-IV of the preceding Figures, showing the splice retaining means. Upstanding flanges 10, 10' contain a channel shaped layer of foam 12, within which is inserted the fibre splice 14. Figure 5 shows the closed closure of Figures 1 to 23. The cover portions 2 and 4 are sealed against each other. The design is very compact, even though the closures of Figure 1 to 3 may be used to contain, for example, up to about 24 splices, or more. Figures 6a and 6b show assembly of the component parts of the assembly of Figure 2, i.e. the assembly comprising cover portions 2 and 4 and a separate storage fray 32. The storage fray 32 is mounted on a connection plate 30 which has two pivot points 40. The connection plate 30 is provided at each end with a resilient projection 42 which can be pushed into and latch against a part 44 on each of the cover portions 2 and 4. By depressing the projection 42, the connection plate 30 can be removed from the latching position, i.e. the connection plate 30, and hence the storage tray 32 is detachably connected to the cover portions 2 and 4. The assembled configuration is shown in Figure 6b. Cover portions 2 and 4 can pivot about points 30 relative to the storage fray 32. Cover portions 2 and 4 can also slide transversely relative to the storage tray 32, i.e. in a direction up and down the page of the figure. The cover portions are shown in the position of maximum spacing from the storage tray 32 in Figure 6b, with the projection 42 on the connection plate 30 abutting against the part 44 on the cover portions 2 and 4. Figures 6a and 6b also illustrate the tongue and groove nature of the mating surfaces of the cover portions 2 and 4, the tongue being indicated by reference number 46 and the groove by reference number 48. A sealing strip 50, e.g. of rubber (e.g. silicone rubber foam), or of gel, or a combination thereof is also included in the groove 48. Figures 7a, 7b and 7c show the assembled parts of Figures 6a and 6b in closed, partially open and fully open position respectively. To go from the fully closed position of Figure 7a to the fully open position of Figure 7c, the cover portions 2 and 4 are first slid transversely relative to the storage tray 32 until the projection 42 on plate 30 abuts the part 44 on the cover 2 or 4. This transverse movement exposes the pivot points 40, and the cover portions 2, 4 can then be pivoted about those points to the position of Figure 7c. This is the fully open position with cover portions 2 and 4 laid flat, and storage fray 32 projecting perpendicularly. This allows easy access. The detachable nature of the connection of the parts 2, 4 and 32 is advantageous since it allows different combinations of cover parts to be put together to perform different functions, e.g. in-line splicing, branching, storage etc. Figures 8a and 8b are perspective views corresponding to Figures 6a and 6b showing assembly of the component parts of the Figure 2 closure. Like reference numbers refer to like parts, and the discussion of Figures 6a and 6b applies directly. Figures 9a, 9b and 9c are perspective views corresponding to Figures 7a, 7b and 7c showing the assembled parts of Figure 8 in closed, partially open and fully open configurations respectively. Like reference numbers refer to like parts, and the discussion of Figures 7a to 7c applies directly.

Claims: CLAIMS 1. A closure assembly for encapsulating splices between optical fibres of one or more fibre optic cables, the assembly comprising first and second hollow cover portions having mating surfaces which can be sealed together around the fibre optic cable(s), wherein one or both of the cover portions is provided with splice retaining means for securing the said optical fibre splices. 2. A closure assembly according to claim 1 , wherein only one of the cover portions is provided with splice retaining means, and the other of the cover portions is provided with loose-fibre retaining means, for storing lengths of loose optical fibre. 3. A closure assembly according to claim 1, wherein both the first and second cover portions are provided with splice retaining means for securing the optical fibre slices. 4. A closure assembly according to any preceding claim, wherein a separate storage tray is provided for storing lengths of loose optical fibre, the storage tray being provided with loose-fibre retaining means. 5. A closure assembly according to any preceding claim, wherein the or each cover portion which is provided with splice retaining means is also provided the loose fibre retaining means. 6. A closure assembly according to any preceding claim, wherein the splice retaining means comprises two substantially parallel upstanding flanges, and preferably a resilient material between the flanges, the optical fibre splices being positioned, in use, within the resilient material. 7. A closure assembly according to any preceding claim, wherein the cover portions are pivotally connected to each other. 8. A closure assembly according to claim 4 or any claim dependent thereon, wherein the additional storage tray is mounted on a connection plate, the connection plate being provided with pivoting and sliding means to allow the storage tray both to pivot and to slide transversely, relative to each cover portion. 9. A kit of parts comprising three or more cover portions, any two of which may be used together for forming a closure assembly for optical fibre splices, each cover portion being provided with a mating surface to seal to another of the cover portions, and being adapted to provide different functions in the closure assembly. 10. A kit of parts according to claim 9, wherein at least one of the cover portions in the kit is provided with splice retaining means. 11. A method of encapsulating splices between optical fibres of one or more fibre optic cables using a closure assembly according any of claims 1 to 8, the method comprising: (i) splicing optical fibres and securing them in the splice retaining means of the or each cover portion, and; (ii)sealing the mating surfaces of the cover portions to each other. 12. A method according to claim 11, using a closure assembly according to claim 5, or any claim dependent thereon, wherein the or each cover portion is provided with both splice retaining means and loose fibre retaining means, the method comprising positioning excess length of the spliced fibre(s) in the loose fibre retaining means in the same cover portion in which the fibre splice of that fibre is retained. 13. A method according to claim 11 or 12, wherein only some of the fibres of the fibre optic cable are spliced, using a closure assembly according to claim 4, or any claim dependant thereon, in which a separate storage tray is provided, the method comprising positioning excess length of unspliced fibre in the said separate fray.

Inventors: ALAERTS ROGER, BUEKERS VALERE, DAEMS DANIEL, NOLF JEAN-MARIE ETIENNE, ROOSEN DIRK, VANONCKELEN MARC, ALAERTS, ROGER, BUEKERS, VALERE, DAEMS, DANIEL, NOLF, JEAN-MARIE, ETIENNE, ROOSEN, DIRK, VANONCKELEN, MARC
Applicants: ALAERTS ROGER, BUEKERS VALERE, DAEMS DANIEL, NOLF JEAN MARIE ETIENNE, RAYCHEM LTD, RAYCHEM SA NV, ROOSEN DIRK, VANONCKELEN MARC, ALAERTS, ROGER, BUEKERS, VALERE, DAEMS, DANIEL, N.V. RAYCHEM S.A., NOLF, JEAN-MARIE, ETIENNE, RAYCHEM LIMITED, ROOSEN, DIRK, VANONCKELEN, MARC
Application year: 1998
Main classification: G02B6
IPC codes: G02B6