WO2000058769A1 - Optical fibre management cassette - Google Patents

Abstract

A cassette (11) for holding a plurality of optical fibre splitters (12, 13, 14), comprises a first part (15) having means (67-73) for receiving optical fibre splitters, first means (51, 52) for guiding optical fibres (45-48) to or from the splitters within the cassette, and a plurality of first ports (21-26) for optical fibres to enter or exit the cassette, and a second part (16) having second means (61-63) for guiding optical fibres to or from the splitters within the cassette and a plurality of second ports (64-66) for optical fibres to enter or exit the cassette. The cassette (11) is compact yet has a high capacity while allowing a modular optical fibre management system.

Description

OPTICAL FIBRE MANAGEMENT CASSETTE

The present invention relates generally to an optical fibre management system, and particularly to a cassette for special-purpose connections between optical fibres.

Optical fibres are increasingly used in communication systems and their use involves various constraints due to the particular nature of optical fibres themselves. One of these is the absolute limit on the minimum bending radius to which the optical fibres can be subject during use and storage in order to maintain their performance. If an optical fibre is bent through a radius less than the minimum bend radius its transmission properties can be permanently impaired. For this reason the components of a management system or distribution centre utilising optical fibres must be carefully designed to ensure that the routes followed by the optical fibres do not require the fibres to be bent sharply. One way in which this is achieved is to leave relatively long lengths of surplus optical cable on either side of a junction so that should reallocation of an optical fibre be required it can be withdrawn from its storage position for work to be undertaken on it before being returned to service.

One of the more critical components of an optical fibre system is the so called 'splitter' which is a special purpose connector for joining one optical fibre to two others to make a branch connection. Splitters are relatively long rigid units which must be protected from vibration and shock in order to maintain their performance; they are very often held in a cassette which also houses the spare lengths of optical fibres to allow subsequent working if maintenance operations or reallocation of the fibres is required after initial installation.

Because of the relatively high density of fibres within a system, and because of the need to identify and gain access to individual fibres or groups of fibres for maintenance and/or reallocation for example for modification or expansion of the system, arrangements in which sub-groups of fibres and connectors are housed in assemblies can have particular advantages. In systems involving splitters the optical fibres leading to the splitters may all arrive from another part of the system in such a way that the splitters can be orientated all facing the same way, or may arrive from different parts of the system, in which case it may be necessary to have splitters, or cassettes containing them, orientated in such a way as to accommodate the arrival and departure directions of the optical fibres to and from the splitters.

EP 0 531 628 discloses an optical fibre organiser whereby an optical fibre cable is located on a lower tray and an optical fibre from the cable is spliced to a pigtail exiting via a plug and socket connection in an upper tray which is pivotably mounted to the lower tray. An intermediate tray is also provided so as to allow storage means for spare length in the pigtail. This document therefore discloses an organiser in which a plurality of ports for optical fibres are provided on only the first part or tray.

WO 95/07480 discloses an optical fibre organiser whereby a longitudinal plate provides a transverse array of guide means for incoming or exiting optical fibres along its length whereby the optical fibres are manipulated in trays which are orthogonally mounted with respect to the length of the plate. This document is not directed towards the problem solved by the present invention. Furthermore, the parts are provided only on its base and the optical fibre guides are provided only on trays carried by the base and constitutes a separate part therefrom.

US 5 790 741 discloses a cassette in which there are provided entry and exit means for one or more optical fibre cables. The cassette further provides guide means for the splicing of optical fibres from the entry and exit cables, but the ports are provided on only one part.

The present invention seeks to overcome the disadvantages of the Prior Art and to provide a cassette for a plurality of optical fibre splitters as defined above which will have a high degree of versatility without loss of modularity in the system. The present invention also seeks to provide a cassette having a high capacity without loss of compactness so that cassettes containing several splitters can be positioned closely adjacent to one another in circumstances where space is restricted, without obstructing access to any given optical fibre or splitter.

According to one aspect of the present invention, therefore, a cassette for holding a plurality of optical fibre splitters as herein defined comprises a first part having means for receiving optical fibre splitters, first means for guiding optical fibres to and from the splitters within the cassette, and a plurality of first ports for optical fibres to enter or exit the cassette, and a second part having second means for guiding optical fibres to or from the splitters within the cassette and a plurality of second ports for optical fibres to enter or exit the cassette.

By proving two sets of ports it is possible therefore to separate the functions of the fibres, should this be required, such that all in coming fibres pass though one set of ports while all exiting fibres pass though the other set of ports, although it would be equally possible to have fibres entering and exiting through either the first or the second ports.

Optical fibre splitters are usually provided with a length or lengths of optical fibres having connectors at their free ends by which the connection to the incoming and exiting fibres of the overall system may be connected. For this reason it is preferred that the first and second ports are adapted to receive respective connector parts for connecting optical fibres within the cassette to optical fibres outside the cassette. The ports referred to above may, therefore, be formed as suitable retainers for engaging or supporting one part of a connector allowing connections to be made to optical fibres within the cassette without opening it.

In a preferred embodiment of the invention the said second part of the cassette is hingedly connected to the said first part thereof along one edge such that the cassette may be opened by turning the second part about the hinged connection to the first part. Alternatively, however, the said second part may be releasably connectable to the said first part whereby to be separated from it entirely when the cassette is opened. In such an embodiment the releasable connection between the first and second parts of the cassette may be achieved by fastening means or by means of co-operating snap engageable elements on the two cassette parts.

In the preferred embodiment of the invention the said first and second ports face in different directions, preferably in opposite directions although it is, of course, within the ambit of the present invention to provide a cassette in which the first and second ports face in the same direction.

Preferably the ports have a substantially rectangular cross section for receiving co- operatingly-shaped connectors. In the preferred embodiment each of the first ports has its longer side orthogonal to the longer side of the second ports. In other words the second ports are turned through 90° with respect to the first ports.

In a particularly convenient configuration the said two cassette parts are substantially planar and one said part has an intermediate step in which the said second ports are located. In such a embodiment the orientation of the step may be such that the second ports face in the opposite direction to the said first ports.

In order to secure the splitters in position on the first part of the cassette there may be provided snap-engageable mountings into which the splitters may be snap-fitted. To provide good protection for the optical fibre splitters the cassette preferably also includes a resilient element located between the splitter and the said first cassette part which is partly compressed by a splitter as it is snap-fitted into position so as to cushion the splitter and protect it from vibration.

At least one of the cassette parts may be provided with means for engaging the cassette to a support member of a carrier tray. Such support member may be an arm or guide upstanding from the carrier tray for locating the cassette in a chosen orientation.

The present invention also comprehends an assembly comprising a plurality of cassettes for optical fibre splitters as defined here-in-above, and a carrier tray having support members for the cassettes and holding them in a predetermined orientation with respect to the tray.

In such an assembly each cassette may be provided on one end face thereof with means for guiding optical fibres leading to or coming from an adjacent cassette whereby to prevent the cables from bending though less than the minimum bend radius for the optical fibres. In an assembly as defined hereinabove in the said predetermined orientation of each cassette it preferably has its major faces lying in a plane orthogonal to the major plane of the tray and inclined at a non-zero angle to one side thereof. It would, of course, be possible for the cassettes to be orientated with their major faces parallel to the general plane of the tray and stacked one above the other in individual stacks, or alternatively for the cassettes to be orientated such that they are orthogonal to the plane of the tray and to the length of the tray. An inclined orientation is preferred, however, as this eases the curvature of the fibres leading to and from the cassette assisting in avoiding the minimum bend radius.

The said cassette support member of the tray may comprise arms in pairs for engaging either side of each cassette, or may comprise generally planar elements having respective elongate slots for receiving engagement means of the cassette whereby to locate and retain a cassette in a predetermined orientation. In such an embodiment the engagement means of the cassette may be studs engaging from at least one major face of the cassette. It is convenient for the studs to be located at selected positions over the face of the cassette for which purpose a snap-engageable stud element may be provided for engagement in one of a number of holes provided in the major face of the cassette.

In the preferred embodiment of the invention the said elongate slots of the cassette support members extend in a direction that is inclined at a non-zero angle to the plane of the carrier trays. This allows each cassette to be introduced to the tray and removed from it by a movement which is inclined to the plane of the tray. This is the most satisfactory direction from an operator's point of view.

The slot may have a lateral branch at or adjacent one end thereof into which the studs can be displaced by a movement transverse the direction of movement along the slot whereby to secure the cassette in position on the tray. One or more slot, or said branch slot, may have a constriction adjacent its end whereby to retain the engagement means of a cassette when introduced into a slot and moved to that end.

Various embodiments of the invention will now be more particularly described, by way of example with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram illustrating one known type of splitter; Figure 2 is a perspective view of a cassette for holding a plurality of optical fibre splitters, formed according to the principles of the present invention; Figure 3 is an enlarged view of a detail of the cassette illustrated in figure 1;

Figure 4 is a perspective view illustrating a detail of the cassette of the invention; Figure 5 is a perspective view of a carrier tray holding a number of cassettes formed as embodiments of the present invention;

Figure 6 is a perspective view illustrating one form of the cassette support member of the tray of Figure 4;

Figure 7 is a side view of an alternative cassette support member; Figure 8 is a perspective view of the cassette support member of Figure 7; Figure 8a is a detail of part of the cassette support member of Figures 7 and 8; Figure 9 is a perspective view of a multi-application housing incorporating a cassette carrier tray holding cassettes formed according to the principles of the present invention; and Figure 10 is a perspective view of a cassette of fitted with a bend radius protector.

Referring first to Figure 1 there is shown a splitter generally indicated 1 which may be a known type of monolithic fusion biconically tapered splitter which is generally cylindrical and up to several centimetres long. The function of the splitter is to divide a signal-carrying optical fibre into two carrying the same signal. Splitters may be provided with up to 1.2 metres of 'pigtail' that is optical fibre having a connector at one end. In Figure 1 the input fibre is indicated 2 with a connector 5 and two output fibres 3, 4 are shown having respective connectors 6, 7. Splitters such as that illustrated in Figure 1 are typically contained within a cassette which holds the splitter securely in position and protects it, stores the surplus pigtail from the input and output side and physically locates the connectors to enable connections to be made with external optical fibres quickly and easily. Because of the size of the connectors there is a physical limit to the number of connectors which can be fitted to one cassette, typically six connectors may be considered as a practical limit which means that the cassette can only carry two splitters each having one input connector and two output connectors.

Referring now to Figure 2 there is shown a cassette generally indicated 11 for housing three monolithic fusion biconially tapered splitters 12 , 13 and 14. The holders for the splitters 12, 13 and 14 are illustrated in more detail in Figure 3 and will be described further hereinbelow.

The cassette 11 comprises a main or base part 15 and an upper or cover part 16. The base part 15 has a generally planar base wall 17 with upstanding side walls 18, 19 at opposite sides thereof and an upstanding rear wall 20. The two side walls 18, 19 have the same height as the rear wall 20 over the majority of their length with a front portion 18a, 19a of approximately twice this height.

At its first end the base part 15 has six ports 21-26 defined between adjacent upstanding elementary wall portions 27 each of which has a transverse flange 28 at its upper end, surmounted by a rib 29 the function of which will be described in more detail hereinbelow.

The part 16 of the cassette 11 is hingedly connected to the rear wall 20 by a suitable hinge such as a ligament hinge (assuming the cassette is made by injection moulding from a suitable plastics material) although other suitable forms of hinge may be employed. The cover part 16 has two substantially planar main wall portions 30, 31 which are offset from one another by a distance equal to the different between the height of the side walls 18, 19 and the (greater) height of the front portions 18a, 19a. The two planar major wall portions 30, 31 are joined by a step 32. The major wall portion 30 adjacent the hinge 33 will be referred to hereinafter as the proximal wall portion and the portion 31 as the distal wall portion. The distal wall portion 31 has two side walls 34, 35 the edges 36, 37 of which are in alignment with the edges of the proximal major wall portion 30 as continuations thereof, and have inclined ends 38, 39 which match corresponding inclined edges 40, 41 joining the side wall 18 to the higher wall portion 18a and the side wall 19 to the higher portion 19a such that when the cover part 16 is turned about the hinge 33 to lie parallel to the base part 15 the edge portions of the proximal major wall portion 30 of the cover part 16 lie over the upper edges of the side walls 18, 19 as do the edges 36, 37 of the side walls 34, 35 of the distal major wall portion 31. A free edge 42 of the distal major wall portion 31 overlies the upper ends of the front wall elements 27 and has a plurality of notches 43 which are shaped to engage over the ribs 29 on the upper faces of the flanges 28 at the ends of the finger-like wall elements 27. Between the notches 43 each edge portion of the free edge 42 has a transversely projecting tooth 44 the purpose of which will be described in more detail below.

When the cover portion 16 is closed over the base portion 15 the finger elements 27 separate six individual rectangular ports 21-26 orientated with their longer edges transverse the major planes of the major walls 17, 30, 31 to receive respective connectors for connecting optical fibres 45, 46, 47, 48 to external optical fibres (not illustrated). The connectors themselves are conventional and are not described in more detail herein, sufficient to say that each comprises two connector parts, one of which is permanently connected to the optical fibres 45, 46, 47, 48 and retained in a port 25-26 by engagement with the tooth 44 and a corresponding tooth 50 formed at the front edge of the major wall portions 17 between each pair of finger-like front wall portions 27 and the other of which is releasably connectable thereto and is permanently connected to an external optical fibre (not shown).

Within the cassette 11 there are provided optical fibre guides in the form of curved walls 51, 52 upstanding from the major wall portion 17 and having co-operating retainer lugs 53 (only one of which is specifically referenced) for guiding spare lengths of the optical fibres 45-48 in a loop from the end of the splitters 12, 13 and 14 to the ports 21-26. The spare loops of optical fibre are not illustrated completely in the drawing, but their paths will readily be deduced by the man skilled in the art. From the other end of the splitters 14 and 15 extend the individual or incoming optical fibres only two of which are shown, identified as fibres 55 and 56. These follow a path as schematically shown under a retainer lug 57 and between two fibre guides 58, 59 on the cover part 16, leading via a further optical fibre guide 60 to three curved guides 61, 62, 63, around which the optical fibres pass on there way to respective ports 64, 65, 66. The ports 64, 65, 66 are rectangular and of the same dimension of the ports 21-26 but have their major sides lying parallel to the major plane of the cover part 16 and thus occupy significantly less height transverse the said major plane. As with the ports 21-26 they will in use house respective known connectors (not shown) for connecting the optical fibres 55, 56 releasably to external incoming optical fibres (not shown). As can be seen in Figure 3 the holders for the monolithic fusion biconically tapered splitters 12, 13, 14 comprise pairs of aligned U-shape brackets 67, 68; 69, 70; and 71, 72 each comprising pairs of resilient arms having an internal curved configuration matching that of the cylindrical wall of the splitter 12, 13, 14 so that each splitter 12, 13, 14 can be snap- engaged into a respective pair of brackets 67, 68; 69, 70; 71, 72. A pad 73 of polymeric resilient material is located between the pairs of brackets 67-72 and is of sufficient thickness to be lightly engaged and slightly compressed by the splitters 12, 13, 14 engaged in the brackets 67-72 whereby to prevent these from moving and to protect them from vibrations.

It is assumed that the splitters 12, 13, 14 are oriented, as shown in Figure 1, with the single input fibres 55, 56 at the end nearer the hinge 33, and the twin, output fibres 45-48 at the opposite end. In such configuration, when the cassette is closed, the input fibres passing through ports 64-66 arrive from one end of the cassette 11, namely the hinge end, and the pairs of outgoing fibres pass through the ports 21-26 at the opposite end. It is, of course, possible to orientate one or more of the splitters 12, 13, 14 oppositely such that the incoming fibres arrive through one or more of the ports 21-26 and, likewise, the ports 64-66 may be traversed by one or more exit fibre.

Referring now to Figure 4 a cassette 11 is shown on edge with its front facing the observer showing the fingers 27 separating the ports 21-26. The cassette 11 is shown in the closed configuration so that the outside of the distal major wall portion 31 can be seen. This has four projecting studs 74, 75, 76, 77 which, as shown by the insert, have respective pairs of resilient legs 78, 79 with laterally projecting teeth 80, 81 for snap-engaging into selected holes 82-85 in the distal major wall portion 31.

Figure 5 illustrates a carrier tray 86 having removable cassette-support members 87 (as shown in Figure 6) having a transverse foot portion 88 with an engaging lug 89 for engagement in a shaped slot 90 in the carrier tray 86. Each support 87 has two inclined slots 91, 92 having upwardly open mouths 93, 94 into which the studs 74-77 can be engaged to retain the cassette 11 in an edge-supported orientation as illustrated in Figure 5. It will be appreciated also that the supports 87 are inclined to the long edge of the carrier tray 86 so that the cassettes 11 are held in an inclined orientation. This facilitates the connection and disconnection of optical fibres thereto.

Moreover, it allows the cassettes 11 to be positioned on the tray 86 by moving them at an angle downwardly from a position spaced to one side which, again, is an advantage for minimising the amount of slack cable required and maximising the accessibility of the connectors and the cassettes.

Figures 7 and 8 show an alternative embodiment of cassette support member 87' having inclined slots 91', 92' with lateral branches 95, 96 and 97, 98 which allow a cassette 11, once lowered into the slots 91', 92' to be drawn forward so that the studs 74-77 engage in the branches 95-98 to be more securely held in position. For this purpose the ends of at least one, and possibly all of the branches 95-98 may be provided with a constriction formed by a slight projection on ridge 99 adjacent to the closed end 100 of the branch, such as the branch 98, past which the co-operating stud can be pushed causing resilient compression of the ridge 99 and of the stud itself so that the stud is held in the end portion 100 against inadvertent displacement.

Figure 9 illustrates a multi-application housing in which a cassette carrier tray 86 housing a plurality of cassettes 11 is incorporated with a fibre optic patch panel generally indicated 101. Curved guides 102, 103 are provided for bend radius control and cable guides 104, 105 for routing the cables are provided at each corner.

Additional bend control may be achieved, as indicated in Figure 10, by providing the hinge end of the cassette 11 with a protector strip 105. This may be a vacuum formed or hot bent sheet comprising a main flange 106 and a v-section free edge portion 107 which is slightly curved to match the minimum bend radius and slightly resilient to allow accommodation in guiding cables and/or optical fibres from an adjacent cassette 11 on its route.

It will be appreciated, of course, that the cassettes 11 may be oriented differently from that shown in Figure 9, in particular they may be reversed (i.e. turned front to back) such that the six inlet ports face away from the observer rather than towards the observer as in Figure 9, and also may be inverted (that is turned about a horizontal axis) and inclined in the opposite direction from that illustrated. It is, likewise, of course, not essential that the cassettes 11 be mounted on a carrier tray on edge, and may be stacked flat should this be appropriate in any specific application. Furthermore, the splitter housing may alternatively be used as a distribution or termination box at the user's choice.

Claims

CLAHWS

1. A cassette (11) for holding a plurality of optical fibre splitters (12, 13, 14) as herein defined, comprising a first part (15) having means (67-73) for receiving optical fibre splitters, first means (51, 52) for guiding optical fibres (45-48) to or from the splitters within the cassette, and a plurality of first ports (21-26) for optical fibres to enter or exit the cassette, and a second part (16) having second means (61-63) for guiding optical fibres to or from the splitters within the cassette and a plurality of second ports (64-66) for optical fibres to enter or exit the cassette.

2. A cassette as claimed in Claim 1, in which the first and second ports (21-26; 64-66) are adapted to receive respective connectors for connecting optical fibres (45-48) within the cassette to optical fibres outside the cassette.

3. A cassette as claimed in Claim 1 or Claim 2, in which the said second (16) part is hingedly connected to the said first part (15) along one edge thereof.

4. A cassette as claimed in Claim 1 or Claim 2, in which the said second part (16) is releasably connectable to the said first part (15).

5. A cassette as claimed in any preceding claim, in which the said first and second (21-26; 64-66) ports face in different directions.

6. A cassette as claimed in Claim 5, in which the said first and second ports (21-26; 64-66) face in opposite directions.

7. A cassette as claimed in any of Claims 2 to 6, in which the ports (21-26; 64-66) have a substantially rectangular cross section for receiving cooperatingly-shaped connectors, and the first and second ports are so orientated that their longer sides are orthogonal to one another.

8. A cassette as claimed in any preceding claim, in which the said two cassette parts (15, 16) are substantially planar and one said part (16) has an intermediate step in which the said second ports (64-66) are located.

9. A cassette as claimed in any preceding claim, in which the means (67-73) for receiving optical fibre splitters includes a resilient element (73) between a splitter (12-14) and the said first cassette part (15).

10. A cassette as claimed in any preceding claim, in which there are provided engagement means (74-77) on one or both cassette parts (15, 16) for engaging the cassette (11) to a support member (87) of a carrier tray (86).

11. An assembly comprising a plurality of cassettes (11) for optical fibre splitters as claimed in any preceding claim, and a carrier tray (86) having support members (87) for engaging the cassettes (11) and holding them in a predetermined orientation with respect to the tray.

12. An assembly as claimed in Claim 11, in which in the said predetermined orientation each cassette (11) lies with its major faces lying in a plane orthogonal to the major plane of the tray (86) and inclined at a non-zero angle to one side thereof.

13. An assembly as claimed in Claim 12, in which the said one side of the tray (86) is a shorter side thereof

14. An assembly as claimed in any of Claims 11 to 13, in which the said cassette support members (87) of the tray (86) comprise upstanding generally elongate or planar elements having respective elongate slots (91, 92) for receiving engagement means (74-77) of the cassette (11) whereby to locate and retain a cassette in a predetermined orientation.

15. An assembly as claimed in Claim 14, in which the said engagement means (74-77) of the cassettes (11) are studs projecting from at least one major face (31) of the cassette.

16. An assembly as claimed in Claim 14 or Claim 15, in which the said elongate slots (91, 92) of the cassette support members (87) extend in an orientation inclined at a non-zero angle to the plane of the carrier tray (86).

17. An assembly as claimed in any of claims 14 to 16, in which each said slot (91, 92) has a transverse branch (95-98) at or adjacent each end thereof whereby to receive and retain the engagement means (74-77) of a cassette (11) located thereby.

18. An assembly as claimed in Claim 17, in which each said branch slot (95-98) has a constriction (99) adjacent its end (100) remote from the said slot whereby to retain the engagement means (74-77) of a cassette (11) when introduced into the slot and moved to the end of the branch slot.