Optical fibres, even when"buffered"with protective coatings to guard against abrasion and impact, are fragile and susceptible to not just to fracture but to attenuation, degradation and even complete transmission failure from bending beyond a minimum radius. Where large optical fibre cables (in some cases containing hundreds of fibres) need to be jointed, correspondingly large numbers of fibres must be exposed, correctly routed, spliced, and throughout the process protected from excessive bending and more generally.

Further, spliced fibres need to be protected as far as possible from any bending or other hazard arising when work is done on other fibres.

In current practice, splices and spare loops of cable are accommodated in trays (also known as cassettes) which can be moved from a storage position in which they are compactly stacked together to an accessible position in which the fibres allocated to the tray can be spliced, re-routed or otherwise worked on, and fibres are routed to the respective trays through resilient plastics tubes of a stiffness sufficient to prevent excessive bending and give general protection. It is difficult to obtain the required bending and other characteristics over the whole temperature range in which installations may need to be made or maintained unless the tubes are at least about 5 mm in diameter, and this imposes a design constraint such that the stacking interval of the trays cannot be much less than about 8 mm.

The present invention provides a means of removing this constraint, and thereby enabling substantially more fibres to be spliced or otherwise managed in the same enclosure volume,

or the use of a smaller enclosure for the same number of fibres.

In accordance with the invention, a device for the management and splicing of multiple optical fibres comprises a stack of trays each capable of accommodating at least one fibre splice and/or at least one fibre loop, each tray being pivoted for movement in a plane parallel to its major surfaces between a storage position in which at least one of its major surfaces closely overlies a major face of another of the trays and an accessible position and flexible guides for protecting fibres adjacent to the trays and is characterised in that at least some of the flexible guides each comprise a series of guide members articulated together for limited relative movement.

The guide members may be, and preferably are, substantially rigid, since the movements required to allow the corresponding tray to be moved between its two positions are achieved by articulation, while the limited movement between adjacent guides ensures that the bending radius remains controlled.

In the storage position, the trays may be arranged in a conventional way with their overlying major surfaces perpendicular to the stacking direction; but we prefer that their major surfaces are substantially inclined to the stacking direction so that the area of the trays is substantially larger than the area of their"footprint" projection on a plane perpendicular to the stacking direction. Preferably the angle between the major surfaces of the trays and the stacking direction is in the range from 50 to 70°, with an optimum value about 60°. The resultant increase in stack height can often be accommodated without any change in the height of the enclosure in which the stack will normally be contained, because typical enclosures are domed and the space at the other end of the stack can be utilised. In favourable cases, this enables two stacks of

trays to be accommodated in an enclosure designed for a single stack of conventional trays.

Thus the invention may allow up to at least three times as many trays to be accommodated in the same size and design of enclosure.

The guide members could be of metal, but for ease of fabrication and freedom from corrosion, suitable plastics materials are preferred. These include, for example ABS (acrylonitrile-butadiene-styrene copolymer), high-density polyethylene, polypropylene, nylons (polyamides of several kinds) acetals, polycarbonates, PVC (polyvinyl chloride), modified (high-impact) polystyrenes and cellulose acetate. If required, stiffness can be increased by using a fibrous filler (for example chopped glass fibre).

The guide members may be open channels or closed tubes, or some of them one and some the other; open channel guide members may if desired be provided with closure members that can be positioned after the fibres are in place for additional protection.

The invention will be further described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view along the stacking direction of a double-stack fibre management device (a plan view, if it is assumed that the stacking direction is vertical and the cables enter from below, as drawn), for clarity showing only one tray in a storage position in one of the stacks and one in an accessible position in the other ; Figure 2 is a diagrammatic view in the direction of arrow 2 in Figure 1 (front view), showing all the trays present in storage position in one of the stacks but only one tray, in an accessible position, in the other; Figure 3 is a diagrammatic view in the direction of arrow 3 in Figure 1 (side view), showing only one of the two stacks of trays;

Figure 4 is an enlarged detail showing the structure a chain of articulated guide members forming part of the device; and Figure 5 shows a single guide member.

In Figures 1-3, minor parts that are unnecessary for the understanding of the invention have been omitted.

The device is designed to fit in a conventional enclosure (sketched at 4 in Figures 2 and 3) that closely approximates a cylinder with a domed"top"5 at the end opposite the cable entry 6 and to utilise almost all the space available within it.

Trays 7,8 are arranged in two stacks and when in the storage position (in which tray 7 is shown) each stack occupies nearly one half of the circular"plan"view ; the trays are inclined at about 30° to the plane of Figure 1, 60° to the"vertical"stacking direction 9, whereby their areas can be increased by about 1/cos 30° or 15% compared with their footprint areas projected onto the plane of Figure 1. In the storage position, the side 10 of the tray closest to the mid- line is highest and the side 11 closest to the wall of the enclosure is lowest; in the accessible position, the end 12 is highest and the end 13 lowest. The envelopes within which two of the trays move are shown at 14 and 15 in Figure 2. The trays are shaped so that the highest part of the topmost trays are accommodated in the domed end 5 of the enclosure.

Cables 16 entering at 6 are prepared, broadly in the usual way, to expose end portions of the fibre-enclosing tubes 17 (assuming a loose-tube type of cable) and of the optical fibres 18, but the tubes are terminated before reaching the level of the tray stack and the"bare"fibres (in practice"buffered"with protective coatings) are routed via fixed protective channels 19 (not shown in full detail) and, in accordance with the invention, are protected at their entry into the trays not by resilient tubes but by articulated chains 20 of guide members, the structure of which will be best understood from Figures 4 and 5.

The chains are made up of guide members (links) 21 moulded from ABS and all identical (except that, like the trays, they are mirror images in the two stacks).

The members are linked together by resilient spigots 22 snapping into sockets 23 ; equivalent fittings are provided on the tray and on the fixed member at the other end of the chain. Each guide member provides a portion of channel for receipt of the fibres entering the corresponding tray, bounded by a base 24, outside wall 25, inside wall 26 and a partial cover 27, and is freely rotatable with respect to the neighbouring guide members until the ends of the outside walls 25 abut (on curvature in the direction shown in Figure 4) or the heel 28 abuts the neighbouring guide member (on curvature in the opposite direction). The minimum radius of the channel, and so the minimum bending radius of the fibres is thus controlled.

In a practical design according to these drawings, the trays are 5 mm thick and have an area of 12,000 mm2, and 72 of them are accommodated in two stacks in an enclosure with an internal diameter of 204 mm and an axial length (measured into the dome) of 350 mm. This enclosure was designed to accept only a single stack 24 trays of about the same area aligned perpendicular to the stacking direction and each 8 mm thick.

Any discussion of the background to the invention herein is included to explain the context of the invention. Where any document or information is referred to as"known", it is admitted only that it was known to at least one member of the public somewhere prior to the date of this application.

Unless the content of the reference otherwise clearly indicates, no admission is made that such knowledge was available to the public or to experts in the art to which the invention relates in any particular country (whether a member-state of the PCT or not), nor that it was known or disclosed before the invention was made or prior to any

claimed date. Further, no admission is made that any document or information forms part of the common general knowledge of the art either on a world-wide basis or in any country and it is not believed that any of it does so, with the exception of the"current practice"described at page 1 lines 20-28.