Field of the Invention

The present invention relates to an optical fibre joint, and in particular to an optical fibre joint for use in passive optical networks.

Background to the Invention

Telecommunications network operators have installed large amounts of optical fibre, particularly in core and backhaul networks, where optical fibre has provide very significant performance and cost advantages over coaxial cable and microwave transmission links. In access networks, advances in digital subscriber line (DSL) technology has made it more difficult to justify wide scale investment in fibre. However, there is a trend for access networks to move from all copper networks to hybrid fibre- copper networks utilising fibre to the cabinet (FTTC) and fibre to the node (FTTN) network architectures, and towards all fibre networks, such as PONs (passive optical networks), which provide fibre to the premises (FTTP).

PON networks require optical fibre joints which can store one or more optical splitters. The optical splitter will comprise an input fibre and a plurality of output fibres, typically 8, 16 or 32 output fibres. Each of these fibres needs to be spliced to a respective fibre from a respective input or output cable and these optical splices also need to be stored securely, such that the fibres are protected so that there is no mechanical damage to the fibre and that no short-term optical losses are induced. Figures 1 & 2 show schematic depictions of a known optical fibre joint 100: Figure 1 shows a front view and Figure 2 shows a side view of the optical fibre joint. The optical fibre joint 100 comprises a base

1 10 and a cover 120 which can be removably connected to the base. A spine 130 is connected to the base 1 10 and a plurality of optical fibre storage trays 140 are connected to the spine. The base comprises one or more input cable ports 1 12 and one or more output cable ports 1 14. Figures 1 & 2 shows that one input fibre cable 200 is received within an input cable port 1 12 and that two output fibre cables 220 are received within respective output cable ports 1 14. The input fibre cable comprises a plurality of fibre cable elements 202, each of which comprises one or more optical fibres. When the input fibre cable is routed into the joint, the sheath of the cable is removed and the fibre cable elements are stored within the optical fibre joint. One or more of the fibre cable elements will be routed to one or more of the optical fibre storage trays, such that the optical fibres held within the fibre cable element(s) can be fed into a storage tray. These optical fibres will be spliced to an input fibre of an optical splitter or will be stored within a storage tray for later use. The multiple output fibres from the optical splitter (or splitters) will be spliced to an optical fibre from an output fibre cable 220. When the FTTP network is deployed, it may be that a splitter with 32 output fibres is used to provide service to just several customers such that there are many optical splitter output optical fibres which are initially unused. These unused output optical fibres will be stored, using a plurality of optical fibre storage trays. Summary of the Invention

According to a first aspect of the invention, there is provided an optical fibre joint comprising: a support member, a plurality of optical fibre storage trays connected to the support member, wherein an optical splitter is received within one of the optical fibre storage trays, the optical splitter comprising one or more input optical fibres and a plurality of output optical fibres wherein, in use: the or each spliced optical splitter output optical fibres and respective optical splice and further optical fibre are stored within an optical fibre storage tray; and the or each unspliced optical splitter output optical fibres are stored within an optical fibre storage apparatus which is external to the plurality of optical fibre storage trays.

The optical fibre joint may comprise a plurality of optical fibre storage apparatuses, with the or each optical fibre storage apparatus being connected to the support member. The or each optical fibre storage apparatus may be connected to the opposed side of the support member with respect to the plurality of optical fibre storage trays.

A plurality of optical splitters may be received within the optical fibre storage trays and each of the plurality of optical splitters may be received within a respective optical fibre storage tray. The unspliced optical splitter output optical fibres from the or each optical splitter may be stored together in a respective optical fibre storage apparatus. A single optical splice is stored in one or more of the optical fibre storage trays and/or two optical splices are stored in one or more of the optical fibre storage trays. The optical fibre joint may be further configured to receive one or more input optical fibre cables and one or more output optical fibre cables. According to a second aspect of the invention, there is provided a communications network comprising an optical fibre joint comprising: a support member, a plurality of optical fibre storage trays connected to the support member, wherein an optical splitter is received within one of the optical fibre storage trays, the optical splitter comprising one or more input optical fibres and a plurality of output optical fibres wherein, in use: the optical fibre joint receives one or more input optical fibre cables and one or more output optical fibre cables; one or more optical fibres from the output optical fibre cables are optically spliced to respective optical splitter output optical fibres; the or each optical splice and the associated optical fibres are stored within an optical fibre storage tray and the unspliced optical splitter output optical fibres are stored within an optical fibre storage apparatus which is external to the plurality of optical fibre storage trays.

Brief Description of the Figures

In order that the present invention may be better understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a schematic depiction of the front view of a known optical fibre joint;

Figure 2 shows a schematic depiction of the side view of a known optical fibre joint;

Figure 3 shows a schematic depiction of the side view of an optical fibre joint according to an embodiment of the present invention;

Figure 4 shows a schematic depiction of the rear view of an optical fibre joint according to an embodiment of the present invention;

Figure 5 shows a further schematic depiction of the rear view of an optical fibre joint according to an embodiment of the present invention;

Figure 6 shows schematic depictions of a number of possible designs for the optical fibre storage apparatuses; and

Figure 7 shows a schematic depiction of the rear view of an optical fibre joint 100' according to this further embodiment of the present invention. Detailed Description of Embodiments

Figure 3 shows a schematic depiction of the side view of an optical fibre joint 100' according to an embodiment of the present invention, which comprises a base 1 10 and a cover 120 which can be removably connected to the base. A spine 130 is connected to the base 1 10: a plurality of optical fibre storage trays 140 are supported from the spine 130. The base comprises one or more input cable ports 1 12 and one or more output cable ports 1 14. One or more fibre splitters are received within a respective optical fibre storage tray.

A plurality of optical fibre storage apparatuses 300 are received on the spine 130: preferably the optical fibre storage apparatuses 300 are located on the opposite side of the spine from the plurality of optical fibre storage trays 140. When the one or more fibre splitters are installed into the optical fibre joint (it would be preferred if this installation were to occur within the controlled factory environment of the joint manufacturer but it should be understood that the optical splitter may be installed into the joint by an engineer in the field) the output fibres of the optical splitter are routed from the storage tray which houses the splitter to an optical fibre storage apparatus. Figure 4 shows a schematic depiction of the rear view of an optical fibre joint 100' according to an embodiment of the present invention in which the 16 output fibres of an optical splitter are routed to four different optical fibre storage apparatuses, with each optical fibre storage apparatus storing a group of 4 fibres 165. Before any customers are connected to the joint, the only optical fibre storage trays which are occupied are those which are storing an optical splitter. For the sake of clarity, Figure 4 shows only a single fibre splitter: it will be understood that an optical fibre joint may store several optical splitters, dependant on the size of the optical fibre joint and the number of outputs of the optical splitters. Figure 5 shows a further schematic depiction of the rear view of an optical fibre joint

100' according to an embodiment of the present invention. Figure 5 shows the optical fibre joint 100' when four customers have been connected to the optical splitter. It can be seen that now only three of the groups of 4 optical fibres are stored within an optical fibre storage apparatus. The other four splitter output fibres will be spliced to a respective output optical fibre cable 220, with each of the optical splices being stored in an optical fibre storage tray.

As further customers are connected to the optical splitter, the fibres stored within the optical fibre storage apparatuses will be removed from the optical fibre storage apparatuses and will be spiced to a respective output optical fibre cable, such that the plurality of optical fibre storage trays will be storing one or more optical splitters and a plurality of optical fibre splices. The unspliced optical splitter output fibres are stored in one of the optical fibre storage apparatuses and not in an optical fibre storage tray.

Known optical fibre joints, and associated jointing techniques, lead to inefficient use of the space within a joint. On deployment, the optical fibre storage trays are used to store the output fibres of the optical splitter. As customers are connected to the network, the optical splitter fibres are transferred to further storage trays in order to be spliced. This leads to a number of splice trays becoming unusable. The length of the joint, and thus the number of fibre storage trays which can be connected to the spine, is limited by the size of the underground footway box within which the joint will be housed.

The use of the fibre storage apparatuses, in accordance with the teaching of the present invention, should allow for more efficient utilisation of the space within the joint as the optical fibre storage trays are only used to store optical splitters and the splices of optical splitter output fibres. Optical splitter output fibres which are not yet spliced are stored in one of the optical fibre storage apparatuses, outside of the optical fibre storage trays. By locating the optical fibre storage apparatuses on the rear of the spine, that is on the opposite side of the spine from where the fibre storage trays are connected to the spine, the addition of the optical fibre storage apparatuses does not reduce the amount of space that could be made available for optical fibre storage trays. The space behind the rear of the spine is conventionally used to store excess lengths of the fibre cable elements of the input fibre cable(s). By securing the optical fibre storage apparatuses to the spine, there should not be any interference between the optical fibre storage apparatuses and any stored lengths of fibre cable elements and/or cable.

Figure 6 shows schematic depictions of a number of possible designs for the optical fibre storage apparatuses 300. For example, the fibre storage apparatus 300A may take the form of a simple circular mandrel, around which the optical splitter output fibres can be coiled. The group of optical splitter output fibres may be secured to the outer surface using a small piece of tape, for example. Alternatively, the fibre storage apparatus 300B may have an annular form such that the optical splitter output fibres can be coiled around the external face of the optical fibre storage apparatus or the optical splitter output fibres can be stored within the space defined by the optical fibre storage apparatus. In a further alternative, the optical fibre storage apparatus 300C may comprise an annular ring arranged around a mandrel, defining an annular region within which the optical splitter output fibres can be stored. In the case of the optical fibre storage apparatus 300B & 300C a slit may be formed within the annular ring in order that the optical splitter output fibres can be inserted into and removed from the optical fibre storage apparatus. A single optical fibre storage apparatus may simultaneously store multiple groups of optical splitter output fibres. For example, the optical fibre storage apparatus may have a plurality of circumferential grooves formed in the surface of the optical fibre storage apparatus such that a group of optical splitter output fibres can be coiled within a respective groove. Alternatively, one or more 'collars' could be placed around the mandrel to define a number of different zones for the optical fibre storage apparatus such that a zone could receive one of the groups of fibres.

In a further embodiment of the present invention the node may be installed or provided without any optical splitters installed. Subsequently, one or more optical splitters may be installed into an optical fibre storage tray. For each of the optical splitters to be installed, the input and output optical fibres of the splitter may be stored within an optical fibre storage apparatus. When the optical splitter is installed into an optical fibre storage tray then the respective optical fibre storage apparatus 300 may be attached to a pin or projection 310 located on the spine. The optical apparatus 300 may be as described above with reference to Figure 6 with a complementary recess 320 which can receive the projection 310 so that the optical fibre storage apparatus 300 can be securely mounted on the spline. A push-fit mechanism can be provided such that the optical fibre storage apparatus 300 can be removably mounted on the spine. Figure 7 shows a schematic depiction of the rear view of an optical fibre joint 100' according to this further embodiment of the present invention in which a plurality of projections 310 are provided on the rear of the spine. It can be seen that an optical fibre storage apparatus 300 has been connected to the uppermost projection, with some of the optical fibres 165 being routed to a fibre storage tray. Such an arrangement allows splitters to be installed as needed, with the necessary number of fibres being installed as and when required. Fibres which are not yet needed can be stored safely within an optical fibre storage apparatus.

It will be readily apparent to the person skilled in the art that the optical fibre storage apparatus may take one of many forms and that the exact form of the optical fibre storage apparatus is not critical to the operation of the present invention.

It will be understood that each of the plurality of optical fibre storage trays may store 1 or 2 splices per tray (or even a larger number of splices). It is well known in the field that optical fibres in joints need some form of protection or management in order to minimise mechanical damage or abrasion and to minimise transient optical losses which may be induced by sudden movement of a fibre. Although not shown in the Figures, it should be understood that the output fibres of the or each optical splitter will be protected by some form of fibre management, for example being housed within a bend limiting tube, whilst being routed from the fibre storage trays to the fibre storage apparatuses.

According to one aspect, the present invention provides an optical fibre joint comprising a support member, a plurality of optical fibre storage trays connected to the support member, where an optical splitter is received within one of the optical fibre storage trays, the optical splitter comprising one or more input optical fibres and a plurality of output optical fibres wherein, in use the or each spliced optical splitter output optical fibres and respective optical splice and further optical fibre are stored within an optical fibre storage tray; and the or each unspliced optical splitter output optical fibres are stored within an optical fibre storage apparatus which is external to the plurality of optical fibre storage trays.