GB2339480A

GB2339480A - Optic fibre guide

Info

Publication number: GB2339480A
Application number: GB9909542A
Authority: GB
Inventors: Peter John Whitesmith; Philip Nigel Karras
Original assignee: BICC PLC
Current assignee: Balfour Beatty PLC
Priority date: 1998-04-30
Filing date: 1999-04-27
Publication date: 2000-01-26
Also published as: GB9909542D0; GB9809129D0

Description

2339480 OPTICAL FIBRE GUIDE The present invention relates to a guide for

optical fibres, especially, although not exclusively, when used in 5 exchanges or similar environments.

When optical fibres (10) are re-routed, in small exchanges or routing enclosures, to different exit ports, the fibres have to cross over one another. Conventionally, the fibres are routed, from the entrance port of the exchange, vertically downwards, in a loop, and then vertically upwards onto a shelf or supporting rack (11). Ideally, the fibres should cross over one another in an orderly fashion, but because the fibres hang in loops, the fibres are liable to become tangled at the loops. In addition, the fibres may also become twisted around themselves, which can further exacerbate the tangle resulting from the crossover of the fibres. A so-called "rat's nestO of fibres can soon result. This is illustrated schematically in Figure 1. This tangling, as well as making maintenance difficult, makes the fibres prone to damage and breakage, as well as leading to an undesirable level of attenuation of the light being transmitted along the optical fibre.

According to the present invention, there is provided a guide for an optical fibre in a looped arrangement, the guide having a body with an arcuate recess provided thereon for receiving and guiding the fibre therein at the bottom of the loop, the guide including means for applying tension to the fibre as it is guided in the recess.

Because the guide allows individual fibres (or bundles or ribbons of fibres) to be kept apart from adjacent fibres, and under tension, the tendency for them to twist and twirl is significantly reduced, if not eliminated altogether. In this way, the fibres do not become tangled while in the looped arrangement - with all its attendant disadvantages - and the fibres cap be crossed over in an orderly manner in a way which also allows for easier maintenance.

2 Preferably the means for applying the tension comprises means for pulling the guide body downwards against the fibre in the recess to apply tension thereto, and may be no more than the weight of the guide body itself, or a weight incorporated therein. A mass between 30 and 500g is considered to be suitable; the least mass found effective is of course to be preferred.

Alternatively, the means for applying the tension may comprise means for pushing the guide body against the fibre in the recess to apply tension thereto.

The guide body may be made from a plastics material or metal and may comprise further guide means for assisting retention of the fibre in the recess.

The guide body itself may be constrained to move only in a pre-arranged vertical plane by suitable fixed guides, as an additional precaution against entanglement by one guide body passing over the top of a neigbour. Suitable fixed guides include vertical plates located between and parallel to neigbouring guide bodies so that they define a slot for each of the guide bodies. Preferably the depth of such slot is in the approximate range from half to three quarters of the width of the guide bodies, to provide sound guidance but not risk engagement of the fibres with the tops of the fixed guides.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is a schematic illustration of the prior art, in which a tangled optical fibre arrangement is present in an exchange; Figure 2 is a schematic perspective view of two looped optical fibres with a guide member provided in accordance with the invention in each loop; Figure 3 is a schematic top view of the guide, with fibres guided therein; Figure 4 is a schematic underside view of the guide, with fibres guided therein; 3 Figure 5 is a schematic cross-section of the guide, along the line V-V of Figure 3; Figure 6 is a schematic side view of an alternative embodiment of the invention; Figure 7 is a sketch of a cabinet showing part of another alternative embodiment of the invention; Figure 8 is an enlarged detail of part of that embodiment; and Figure 9 is a further enlarged perspective view of the guide body used in this embodiment.

Figure 2 illustrates a number of fibres 1 re-routed in an exchange. In this instance, only two fibres 1 are shown, for clarity, although, in practice, many more fibres would be present. Also for clarity, the entrance and exit ports of the exchange, as well as the exchange housing and all other apparatus commonly associated therewith are not illustrated. As these features are not directly associated with the present invention, and are well known to persons skilled in the art, they are not described in any further detail herein.

The fibres 1 are routed, in the exchange, to different exit ports than their input ports. As described above, in order to reach the respective exit port, the fibres 1 may have to cross over one another. As in conventional exchanges, and as described above, the fibres 1 hang vertically from the entrance port section of the exchange, and follow a loop 6 before being routed along an horizontally arranged rack 2, to the respective exit ports.

At the bottom of each individual fibre loop 6, a -free standing" guide member 3 is mounted, around which the individual fibre 1 is guided.

The guide 3 has a substantially U-shaped cross-section, with a V-shaped groove or recess 4 provided on its outer surface 5. The guide 3 is placed in the loop of fibre 1 such that the fibre 1 is then received in the recess 4. To maintain the guide 3 in the loop of fibre 1, as well as to keep the fibre 1 in the recess 4 and also to provide tension 4 to the fibre 1, the guide is suitably weighted. Gravity forces the guide 3 downwards in the direction of the arrow in Figure 2, thereby providing suitable tension to the optical fibre guided in the recess 4, as well as keeping the fibre i n the groove. The mass of the guide provides the required tension to the fibre 1. For a conventional optical fibre used in data and telecommunications transfer, in order to keep the fibres taut without straining a mass of around 100500g, and preferably, between 100-200g is required.

By providing each fibre 1 with a weighted guide 3 in the fibre loop 6, each individual fibre 1 is prevented from twisting around itself, and is also spaced, from other adjacent looped fibres. Each fibre 1 can then be routed upwards from the loop 6 towards the support rack 2 where the fibres 1 can be crossed over in an orderly fashion, for example, in the upward vertical plane, A, after the guide 3, and before they are routed along the horizontal rack 2, or on the rack 2 itself. The crossover in the fibres then be carried out in an orderly manner, thereby avoiding tangles, as well as allowing the engineer carrying out any re-routing work, easy access to the fibres to carry out the work.

The guide 3 is made of a smooth plastics material and, in order to provide the required weight, a metal insert is provided in the centre of the guide, for example, using a 4mm slice off a 50mm square mild steel rod.

The use of a smooth plastics material reduces friction between the fibre 1 and the recess 4, thereby allowing easier travel of the guide 3 along the fibre 1.

The radius of curvature of the recess 4, is selected to ensure that the fibres are looped without any light attenuation. For example, in the United Kingdom, the standard bend radius, in BT practice, is 30mm.

In order to improve the introduction of the fibre 1 into the recess 4, and to improve retention of the fibre 1 in the recess 4, fingers or other auxiliary guides (not shown) can be provided at the side of the recess 4, as generally as described below in connection with Figure 9.

As will be understood by a person skilled in the art, various modifications are possible within the scope of the present invention. For example, the weighted guide 3 can be of other shapes and configurations.

Figure 6 illustrates one other suitable embodiment. The guide 3, in this embodiment, is circular, with the recess 4 being provided circumferentially.

The recess 4 could be U-shaped, or any shape suitable to hold and guide the fibre 1. The guide 3 can be dimensioned and shaped to receive a single fibre, or a bundle or ribbon of fibres.

Rather than being "free-standingff, the guide 3 can be movably secured to the exchange housing. The tension can then alternatively be applied to the fibres through the guide 3 by either pushing or pulling the guide downwards, for example, using a spring, or other suitable means, connected to the guide. Alternatively, the guide 3 can be configured to move against the fibre, thereby applying the tension to the fibre, in a horizontal, or any other, direction. The guide 3 can be arranged to move up and down, to allow for differing levels of the horizontal support 2, as well as for tolerance. Minor back-and-forth movement may be allowed, for.

example to help with re-threading in the recesses.

The guide 3 could also be arranged to rotate (in the manner of a pulley wheel) as well as, or instead of, having a smooth recess surface to facilitate travel of the fibre 1 in the recess 4.

Figure 7 shows a telecommunication cabinet 12 in which fibres may be installed (in a generally conventional manner) so as to form loops each extending from a common upper offset shelf 13 to a selected one of lower aligned shelves 14; the bottom of each loop is controlled by a guide assembly 15 in accordance with te invention, which is shown in more detail in Figure S. It comprises 25 (or whatever number is required) 6 of guide bodies 16, but for clarity only one-of them and the components associated with it is shown. The guide body 16 is shown in Figure 9 in a perspecive view showing it in a position chosen to make its shape clear: in use the edge 17 forms the boundary between a visible vertical surface 18 and an invisible horizontal top surface. The guide body comprises a plastics moulding with a smooth U-shaped groove 19 for the reception of a fibre 20. Alternately- directed auxiliary guides 21 secure the fibre against accidental escape form the groove, without making insertion or intentional removal too difficult. Lobes 22 define an internal recess 23 dimesioned, in this example, to accept a 4-mm thick M32 plated steel washer as a snap fit, entering from the top, to weight the guide body.

The guide body is loosely located between guide plates 23 (returning to Figure 8) defining a slot 24 between them with a depth such that about 40% of the width of the guide body projects from it in the freely hanging position; it can be pulled out completely if and when required for threading or modification.

Claims

7 CLAIMS

1. A guide for an optical fibre in a looped arrangement, the guide having a body with an arcuate recess provided thereon for receiving and guiding the fibre therein at the bottom of the loop, the guide including means for applying tension to the fibre as it is guided in the recess.

2. A guide as claimed in claim 1, wherein the means for applying the tension comprises means for pulling the guide body downwards against the fibre in the recess to apply tension thereto.

3. A guide as claimed in claim 2, wherein the guide body includes a weight incorporated therein, whereby the guide body is pulled downwards under the influence of gravity, thereby acting on the fibre in the recess to apply tension thereto.

4. A guide according to claim 1, wherein the mass of the weighted guide is between 100 and 500g.

5. A guide as claimed in claim 1, wherein the means for applying the tension comprises means for pushing the guide body against the fibre in the recess to apply tension thereto.

6. A guide as claimed in any preceding claim, wherein the guide is made from a plastics material.

7. A guide according to any preceding claim, comprising further guide means for assisting retention of the fibre in the recess.

8. A guide for an optical fibre in a looped arrangement substantially as described with reference to Figures 2-5.

9. A guide for an optical fibre in a looped arrangement substantially as described with reference to Figure 9 A guide assembly comprising a plurality of guide bodies as claimed in any one of claims 1-9 and fixed guides for constraining them to move only in a pre-arranged vertical plane 11 A guide assembly as claimed in claim 10 in which the fixed guides are vertical plates located between and parallel 8 to neigbouring guide bodies so that they define a slot for each of the guide bodies. 12 A guide assembly as claimed in claim 11 in which the depth of such slot is in the approximate range from half to 5 three quarters of the width of the guide bodies. 13 A guide assembly for optical fibres substantially as described with reference to Figures 7-9.