GB2300488A

GB2300488A - Optical fibre management system having splice tray and splitter mat

Info

Publication number: GB2300488A
Application number: GB9509118A
Authority: GB
Inventors: Michael Keegan; Martin Perry
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1995-05-04
Filing date: 1995-05-04
Publication date: 1996-11-06
Anticipated expiration: 2015-05-04
Also published as: GB9509118D0; GB2300488B

Abstract

An optical fibre management system comprises at least one optical fibre splice tray, a housing that encloses the or each splice tray, and a splitter mat that contains one or more optical fibre splitters. The splitter mat has a side part 30 that is adapted to be located on a side of the housing in a plane generally perpendicular to the plane of the or each splice tray and has entry guide elements 42 extending along an edge thereof for guiding fibres from the tray to the or each splitter, wherein the splitter mat includes a generally planar top part 36 that extends in a plane parallel to that of the or each splice tray and is adapted to be located adjacent to the tray or one of the trays. The splitter mat has guide surfaces that guide a fibre from one entry guide element to another entry guide element via the top part 36 of the splitter mat where the fibre is bent. The housing may enclose a number of splice trays stacked together. Splitter location 48 (56, Fig. 5) is shown.

Description

OPTICAL FIBRE MANAGEMENT SYSTEM This invention relates to the management of optical fibres.

One form of optical system that is currently being developed is a passive optical network (PON), i.e. a network that does not contain any active electronics in the network which would restrict bandwidth, which network incorporates a number of optical splitters which allow branches to be made in the network, for example branches to individual customers or branches to enable testing of the network. The adoption of a splitter-based system requires a high degree of management of the optical fibres, and for this reason an optical fibre management system is being developed in which fibres are led to and from the splitters by means of a plurality of splice trays or cassettes. In view of the high cost of the optical splitters, these are located in a splitter mat, which is intended not to be accessed in the field.The system includes a stack of splice trays enclosed in a housing on which the splitter mat is located in a plane generally perpendicular to the splice trays, and the splitter mat has an array of entry guide elements extending along an edge thereof for guiding fibres from each of the splitters to one of the splice trays. When the PON is set up or is modified, splitters can be incorporated into the network by forming splices to those optical fibres that extend from the trays to the splitter mat, and housing the splices in the trays.

In this management system stacks of ten or more splice trays are employed even if fewer splice trays are actually needed. The reason for this is that as the optical fibres extend over the splitter mat they must be bent through 1800 in order to enter and exit the splitter mat through the same array of entry guide elements, and the splitter mat must therefore have a height of at least 60mm in order to accommodate a minimum optical fibre bend radius of 30mm.

According to the present invention, there is provided an optical fibre management system which comprises at least one optical fibre splice tray, a housing that encloses the or each splice tray, and a splitter mat that contains one or more optical fibre splitters, the splitter mat having a side part that is adapted to be located on a side of the housing in a plane generally perpendicular to the plane of the or each splice tray and which has entry guide elements extending along an edge thereof for guiding fibres from the tray to the or each splitter, wherein the splitter mat includes a generally planar top part that extends in a plane parallel to that of the or each splice tray and is adapted to be located adjacent to the tray or one of the trays, the splitter mat having guide surfaces that guide a fibre from one entry guide element to another entry guide element via the top part of the splitter mat where the fibre is bent.

The system according to the present invention has the advantage that since the fibres are bcnt through 1800 (or more) in the p!ane of the splice trays, there is essentially no restriction on the height of the splitter mat, and therefore no minimum limit on the number of splice trays that are stacked together. Thus, for example, in a typical arrangement for taking a single tap from the loop, a stack of three splice trays may be employed, one splice tray being employed to house splices in fibres between the splitter and the loop in one direction, another splice tray being employed to house splices in fibres between the splitter and the loop in the other direction and the third splice tray being employed to house splices in fibres extending between the splitter and the customer or other equipment requiring the tap.

The top part and the side part of the splitter mat are advantageously joined along one edge of each part each part extending in a plane that is perpendicular to the plane of the other part, and the guide surfaces are arranged to guide the fibres along the edge where the fibres pass between the side part and the top part. Because the fibres are guided along the edge, i.e. at only a small angle to the edge, the fibres can pass between the two parts of the splitter mat without being bent with a bend radius below the minimum acceptable value of 30mm.

The splitter mat is preferably enclosed to prevent access to the fibre splitters during installation and operation of the system. For example the top part of the splitter mat, which extends in the same plane as the splice trays, is preferably adapted to be located between the housing and an end splice tray of the stack. In addition, or alternatively, the systerr may include a cover that extends over part of the splitter mat, for example over the side part, to prevent access to the splitter. Also, it is preferred for the top part of the splitter mat to have generally the same profile as that of the splice trays. This enables the splitter mat to be housed relatively easily next to the splice trays, and ensures that the top part of the splitter mat is large enough to enable the optical fibres to be bent back on themselves.

If desired a number of different designs of splitter mat may be employed in which the height (i.e. dimension normal to the plane of the splice trays) of the side part varies in order to accommodate different numbers of splice trays in the system.

The reason for this may be due, for example, to the use of higher split ratio splitters.

Alternatively, however, a single design may be employed and the side part of the splitter mat may be provided with one or more separately formed extension pieces to cater for different numbers of splice trays.

In many circumstances the splitter may have additional functionality. For example, the splitter(s) may be a wave division multiplexer in which for example traffic at a wavelength of 131 on is multiplexed with test signals at a wavelength of 1550nm.

One form of optical fibre management system according to the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows schematically part of an optical circuit in which the management system is employed; Figure 2 shows schematically part of an optical management system in which a stack of splice trays is used to organise the fibres; Figure 3 shows a splice tray or cassette that is used in the system; Figure 4 is a perspective view of a splitter mat employed in the management system according to the present invention; Figure 5 is an exploded view of a modified sub-assembly according to the invention employing a splitter mat similar to that shown in figure 4; and Figure 6 is a perspective view of the splitter mat of figure 4 with a number of extension pieces.

Referring to the accompanying drawings, figure 1 shows schematically part of a loop topology passive optical circuit (PON) in which a number of fibres 1, 2, 3 and 4 are arranged in a loop extending centred on an exchange (not shown). As shown, the pair of fibres 4, is accessed to provide four pairs of fibres a, 5b, 5C and 5d which extend to four different customers. This is achieved by means of a 2 x 4 splitter array sub-assembly 6 in which the main and the standby go fibres 4'are al bi combined and split into four go fibres 5awl, 5bl etc and the main and standby return fibres 4 are similarly combined and split into four return fibres 5ally 5bll etc by means of 2 x 4 splitters.One such splitter array sub-assembly as previously proposed is shown in figure 2 and an individual splice tray is shown in figure 3. The assembly comprises a housing 8 including a top plate 10, bottom plate 12, and a back plate, and a numbel of splice trays 14, each of which has an entry region 16, a clip-on test region 17, a region 18 for looping the fibres in such a way that they are not bent with a radius below the minimum bend radius, and a region 20 for accommodating splices in the fibres. The splice trays 14 are designed so that the fibres can be accommodated in generally oval loops or 'figure of eight' loops in order that different fibres can be presented to one another in line in the region of the splice and yet all fibres will enter the splice tray at the same entry region 16. In addition, spare fibre may be housed in the trays.

A generally planar splitter mat (not shown) is located on the back plate of the sub-assembly. The purpose of the splitter mat is to house the splitters together with, parts of the fibres extending to the splice interconnections, i.e. the parts of the go and return fibres 4 of the loop that are located either side of the splitters, and the parts of the additional fibres 5 extending from the splitters, and to direct the relevant fibres toward the entry regions of the splice trays. Fibres extend from the splitter mat to the splice trays via bend limiting tube manifolds 22 and flexible loose tubes (not shown) that extend between outlets 24 in the manifolds 22 and entries 16 of the splice trays 14.In this way it is not necessary to gain access to the splitter when the system is being installed in the field: the field engineer simply installs the subassembly as a whole and forms splices between the ends of the fibres that are located in the relevant splice trays and additional fibres that are routed to the trays through routing tubes.

For the configuration shown in figure 1, a sub-assembly containing six splice trays would be needed, one splice tray to accommodate splices between loop main fibres and the splitters, a second to accommodate splices between loop standby fibres a b and the splitters, and one tray for each of the four pairs of fibres 5a, 5b etc to the customers. The splice trays are typically 8mm in height with the result that the stack of trays will be 48mm in height. However, a minimum height of 60mm is needed to allow for a minimum bend radius of 30mm in the fibres (corresponding, in practice, to a splitter mat height of about 80mm) with the result that a sub-assembly having at least eight splice trays must be used and a number of the splice trays remain empty.

One form of splitter mat according to the present invention is shown in figure 4 and a sub-assembly employing such a splitter mat (or, more precisely, a slightly modified form of such a splitter mat) is shown in figure 5. This splitter mat has a side part 30 that is generally flat but whose ends 32 and 34 are curved to follow the shape of the sub-assembly, and a generally planar top part 36 that is joined to the side part 30 along an edge 38. The height of the side part 30 is reduced so that it is only approximately 24mm high, corresponding to the height of a stack of three splice trays, and the profile of the top part 36 approximates to the profile of the splice trays themselves.In this form the splitter mat can be located on a sub-assembly of reduced height in such a way that the side part 30 is located on the back plate 40 of the subassembly and the top part 36 is located underneath the top plate 10 of the subassembly housing (a suitable recess 41 is provided in the top edge of the back plate 40 for insertion ofthe top part 36 ofthe splitter mat between the top plate 10 ofthe sub-assembly housing and the top splice tray of the stack).

The side part 30 of the splitter mat has guide elements 42 extending along one end 32 thereof for receiving optical fibres from the splice trays. Additional guide surfaces 44 are provided to guide the fibres to the top edge of the side part 30 so that, at the top edge, the fibres are generally in line with the edge, and can then be routed around the top part 36 of the splitter mat without having been bent with too small a bend radius. The fibres are then guided either by means of guide surface 46 alone to one end of the splitter location 48, or in a figure of eight configuration by means of guide surfaces 46,50 and 52 to the other end of the splitter location 48. By this means the number of splice trays in the sub-assembly can be reduced while ensuring the bend radius of the fibres always remains at least 30mm.The sub-assembly is supplied with a splitter mat back cover 53 and bend limiting manifolds 55 provided so that the splitters themselves are not accessible.

The fibre guide elements 42 are provided with recesses 57 through which the fibres extend. The recesses may be filled with an RTV silicone after the fibres have been installed in order to prevent any strain on the fibres being transmitted to those parts of the fibres inside the splitter mat, but also to provide some degree of tensile strain relief to the fibres.

As shown in figure 5 the splitter mat may be provided with small holes 59 and 61 which co-operate with pins in an installation jig, so that fibres can be laid around the pins of the jig during installation and after removal of the splitter may from the jig the fibres will have a predetermined degree of slackness in the splitter mat.

It is not essential for the splitters to be located in the top part 36 of the splitter mat. As shown in figure 4 a diagonal recess 56 is provided in the side part for receiving the splitters.

It is possible to combine the splitter mat with one or more extension pieces 57 and 62 as shown in figure 6 so that it can be increased to fit any size of sub-assembly housing. The side part 30 of the splitter mat has a fibre entry guide 58 at its bottom edge which co-operates with a fibre guide 60 on the extension piece 57 to guide fibre from the extension piece to the side part of the splitter mat.

A number of extension pieces 62 and 56 of different sizes may be combined together as shown in figure 5 to cater for any number of splice trays. As shown in figure 5 seven extension pieces 57 and one extension piece 62 enable the splitter mat to be employed with a sub-assembly containing 26 splice trays.

Claims

Claims:

1. An optical fibre management system which comprises at least one optical fibre splice tray, a housing that encloses the or each splice tray, and a splitter mat that contains one or more optical fibre splitters, the splitter mat having a side part that is adapted to be located on a side of the housing in a plane generally perpendicular to the plane of the or each splice tray and which has entry guide elements extending along an edge thereof for guiding fibres from the tray to the or each splitter, wherein the splitter mat includes a generally planar top part that extends in a plane parallel to that of the or each splice tray and is adapted to be located adjacent to the tray or one of the trays, the splitter mat having guide surfaces that guide a fibre from one entry guide element to another entry guide element via the top part of the splitter mat where the fibre is bent.

2. A system as claimed in claim 1, wherein the housing encloses a plurality of splice trays that are arranged in a stack.

3. A system as claimed in claim 2, wherein the top part of the splitter mat is adapted to be located between the housing and an end splice tray of the stack.

4. A system as claimed in any one of claims 1 to 3, wherein the top part and the side part of the splitter mat are joined along one edge of each part, and the guide surfaces are arranged to guide the fibres along the edge where the fibres pass between the side part and the top part.

5. A system as claimed in any one of claims 1 to 4, which includes a side cover that extends over the side part of the splitter mat.

6. A system as claimed in any one of claims 1 to 5, wherein the top part of the splitter mat has generally the same profile as that of the splice trays.

7. A system as claimed in any one of claims I to 6, wherein the side part of the splitter mat includes one or more separable extension pieces.