Optical fibre manifold

[0001] The present invention relates to manifolds for optical fibres.

[0002] According to the present invention, there is provided an optical fibre manifold arranged to spread optical fibres from a single dimensional ribbon array to a two dimensional block array, wherein the fibre spacing in the block array is the same as the fibre spacing in the ribbon array.

[0003] A benefit of the invention is that each of the optical fibres of the ribbon array are only deflected in a single planar direction.

[0004] A further benefit is that a maximum dimension across the optical fibres in the block array is substantially the same as a dimension across the ribbon array parallel with said maximum dimension.

[0005] A benefit of the optical fibres being deflected only in the single planar direction is that it enables the device to scale in size without limit to accommodate any size of ribbon fibre with no additional impact on the optical performance due to the effects of scale.

[0006] A further benefit is that the device need only scale in size in one direction in order to accommodate all ribbon fibres of a given construction. This simplifies the tooling required to manufacture a range of different sizes.

[0007] Preferably the block array is comprised of a block arranged so that each optical fibre may pass through the block and into a flexible tube.

[0008] Preferably an end of each of the flexible tubes is mounted to the block.

[0009] A benefit of this that small diameter optical fibres may be separated out and fed through flexible tubes having a larger external diameter, and hence providing protection and improved ease of handling for each of the optical fibres.

[0010] Preferably the block array comprises holes through which the optical fibres may pass, arranged in rows.

[0011] A benefit of this is that the number of rows may be varied in a particular embodiment to accommodate a particular difference between the spacing of the optical fibres and an external diameter of the tubes.

[0012] Preferably the manifold is symmetrical about an axial plane.

[0013] A benefit of this is that the number of different components that are required to be manufactured may be minimised.

[0014] Preferably the manifold is provided with a strain relief to ensure that the ribbon array is located securely to the manifold.

[0015] A benefit of the strain relief is that optical fibres within the manifold may remain in an unstressed condition.

[0016] Preferably the manifold is provided with bend radius control at ribbon fibre input to prevent damage to the fibres and the ribbon coating or sheath.

[0017] Preferably the manifold is provided with bend radius control at the fibre exit to prevent damage to the individual fibres principally through the action of bend strain while under tension.

[0018] A benefit of bend radius control is that a risk of damage to the optical fibre is reduced.

[0019] Preferably the manifold is provided with a sleeve, through which the ribbon fibre passes prior to entering the body of the manifold. The sleeve is preferably made of a suitably sized flexible and compressible material.

[0020] A benefit of the sleeve is that it will provide padding and reduce the contact pressure due to irregularities between the fibres contained within the ribbon, the coating or sheathing material used to create the ribbon and the body of the manifold when the ribbon fibre is bent under tension by the manifold.

[0021] Preferably the sleeve is of sufficient length to cover the ribbon cable extending beyond the bend radius region.

[0022] A benefit of the sleeve extending along the ribbon cable is that the sleeve will effectively protect the fibres within the ribbon even if damage to the ribbon coating or sheath is incurred.

[0023] A further benefit is that the risk of damage to the ribbon construction is reduced and in the event of the ribbon construction failing the functionality of the device is maintained. A further benefit is that the operational life of the product is extended.

[0024] Preferably a support guide is provided within the manifold to closely support each optical fibre. More preferably the support guide is arranged to support each optical fibre such that the fibre follows a smoothly curving path through the manifold.

[0025] A benefit of this is that each of the optical fibres is routed through the manifold with no micro-bends that would cause damage to the optical fibres or reduce the transmission of light through the optical fibres.

[0026] A further benefit is that in use, any axial force on an optical fibre within a tube leaving the manifold is prevented from deflecting the fibre from the smoothly curving path. Hence, a risk of degradation of transmission of light in service may be avoided.

[0027] Specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

[0028] FIG. 1 is a perspective view of a first manifold according to the invention;

[0029] FIG. 2 is a perspective view of a block array of the manifold shown in FIG. 1;

[0030] FIG. 3 is an end view of the block array shown in FIG. 2 showing the layout of holes to receive tubes;

[0031] FIG. 4 is a longitudinal sectional view of part of the manifold of FIG. 1;

[0032] FIG. 5 is a perspective view of a support block for use with the manifold shown in FIG. 1;

[0033] FIG. 6 is a perspective view of a second manifold according to the invention;

[0034] FIG. 7 is a perspective sectional view of the second manifold; and

[0035] FIG. 8 is a further sectional view along a longitudinal axis of the second manifold.

[0036] From FIG. 1, a perspective view of a manifold 1 can be seen to comprise a housing 2 formed from two identical mouldings 3 and 4, and a block 210. A ribbon cable 20 enters the housing at an entry opening 22, and passes through a strain relief block 24 through a support 25 and then enters a fanout chamber 26 where individual optical fibres 31 to 42 inclusive are separated from each other and led to their respective holes 231 to 220 respectively. The ribbon cable 20 comprises twelve optical fibres arranged in a linear array. Each optical fibre is protected by a plastics coating, and attached along an axial joint line on the circumference of each optical fibre. Inserted into each hole from a direction of arrow A are tubes 51 to 62 inclusive, each of which tubes receive an optical fibre 31 to 42 respectively. The tubes provide protection to the optical fibres as they are led away from the manifold. Each tube is 0.9 mm in diameter, but may be as small as 0.6 mm or less. Each tube has a bore with a diameter of 0.4 mm to allow clearance between the optical fibre which has an external diameter of 0.25 mm.

[0037] The strain relief block 24 comprises an elastomeric tubular sleeve that conforms closely to an external profile of the ribbon array, and is retained securely to the ribbon array. A suitable method of retention would be to use an adhesive or compression applied by a clip or the body of the manifold.

[0038] The elastomeric tubular sleeve is securely retained in a recess within the housing when the housing is closed around the ribbon array. Means (not shown) are provided to securely fasten each of the mouldings 3 and 4 to each other when assembled, examples of suitable such means being by a snap fit arrangement, screws, clips or adhesives. Each of the mouldings is provided with a location peg and socket to receive the peg of the other moulding. Hence alignment of the two mouldings is ensured.

[0039] FIG. 2 shows a perspective view of the block array 210. Recess 240 is provided to co-operate with a protrusion on an internal surface of the housing to locate the block array within the housing. Preferably the block is symmetrical about a longitudinal axis parallel to an axis of a hole for an optical fibre. More preferably the block is also symmetrical about an axis perpendicular to said longitudinal axis.

[0040] From FIG. 3 an end view along arrow A of the block array 210 is shown with the layout of holes 231 to 220 to receive tubes 51 to 62 and optical fibres 31 to 42 respectively. Layout lines 205 are shown to illustrate the arrangement of the holes. Dimension x is equal to the pitch of the optical fibres in the one dimensional array of the ribbon cable, which in this embodiment is 0.25 mm, and dimension y is equal to three times the dimension x and hence dimension y is 0.75 mm and dimension z is equal to four times the dimension x, hence in this embodiment 1.0 mm. Block 210 has dimension a is 3.75 mm and dimension b is 3.90 mm and dimension c and d are each 6 mm and length of the housing is dimension e which is 25 mm.

[0041] The relationship between the dimensions x, y and z may be expressed as a general formula which would apply to other embodiments of the invention where because of a different ratio of tube diameter to pitch of the optical fibre ribbon array, a different number of rows of holes are required in the block array. Hence the general formula would be:

[0042] where:

[0043] n is the number of rows in the block array

[0044] x is the pitch of the optical fibres in the ribbon array

[0045] y is the dimension parallel to a transverse plane of the ribbon array between the centres of n holes

[0046] z is the dimension parallel to a transverse plane of the ribbon array between the centres of adjacent holes in the same row

[0047] The pitch of the optical fibres, shown as dimension X, is the spacing of the optical fibres in the one dimensional array of the ribbon cable, and is also the spacing of the optical fibres in the two dimensional array of the block array.

[0048] From FIG. 4 a section from a side of the manifold 1 showing four of the holes in the block array 210 in section. Support 25 has a radiused edge facing the chamber 26 to minimise a risk of damage to the optical fibres.

[0049] FIG. 5 shows a diagrammatic view of a support block 80, having four support channels 81, 82, 83 and 84 to support four optical fibres 85, 86, 87 and 88 respectively between the support 25 and the block 210. In use two identical support blocks 80 and 80 (shown in dotted line) are used facing each other to ensure that each of the optical fibres is guided along an optimum path with optimum bend radii along the path. For manifold 1, where the optical fibre ribbon array cable comprises 12 optical fibres, three support blocks are required below the cable and three support blocks are required above the cable.

[0050] In an alternative embodiment similar to that of manifold 1, the support block is formed as part of the housing moulding.

[0051] From FIG. 6 a perspective view of a second manifold 600 according to the invention. Manifold 600 comprises a housing 602 formed from two identical mouldings 603 and 604. The two mouldings are held together with a pair of identical clips 606 and 608 that locate in recesses 610 and 612. A ribbon cable 620 enters the housing at an entry opening 622, and passes through the manifold where individual optical fibres 631 to 654 inclusive are separated from each other leave the manifold at an exit opening 662. The ribbon cable comprises twenty-four optical fibres 631-654 arranged in a linear array at the entry to the manifold, the fibres being displaced in a single planar direction indicated by arrow 6P to spread the fibres to a two dimensional block array 664 at the exit from the manifold. The block array having a height 6H and a width 6W. The width 6W being the same as a width 6R of the ribbon cable.

[0052] FIGS. 7 and 8 are sectional views of the second manifold 600 and show strain relief means 614 for resisting an axial movement of the ribbon cable in the direction of arrow 6A, the strain relief means 614 being retained in recess 616 in the housings. The housings 603 and 604 are provided with an entry bend radius 624 at the entry opening 622. A dimension 6N of the entry bend radius is arranged to be sufficiently large so that when the ribbon cable is bent around the bend radius no damage will occur to the optical fibres 631 to 654, or to a ribbon coating or sheath 621. To further protect the ribbon cable an entry sleeve 626 is mounted over the ribbon cable 620. The entry sleeve preferably extends a length 6S along the ribbon cable such that support is provided to the ribbon cable should it be bent so as to contact edge 625 at an end of the entry bend radius 624.

[0053] The housings 603 and 604 are provided with an exit bend radius 684 at the exit opening 662. A dimension 8N of the exit bend radius is arranged to be sufficiently large so that when an optical fibre 631 to 654 is bent around the bend radius no damage will occur to the optical fibre. To further protect the optical fibres an exit sleeve 686 is mounted over each of the optical fibres 631 to 654. The exit sleeve preferably extends a length 6L along each of the optical fibres such that support is provided to each optical fibre should it be bent so as to contact edge 685 at an end of the exit bend radius 684. The exit sleeves are flexible tubes.

[0054] Mounted to the housings 603 and 604 is a block 690 having twenty-four parallel holes (only 691 labelled), each hole having a longitudinal axis parallel with a longitudinal axis 6X of the manifold. The holes are arranged so that the optical fibres are spread from the single dimensional array of the ribbon cable at the entry opening 622 to the two dimensional block array 664. Preferably the exit sleeves are retained to the block, for example by means of adhesive or another suitable method.

[0055] From FIG. 8, it can be seen that each optical fibre is displaced in a smooth curve at 8C within the manifold. Each optical fibre is only displaced in a single planar direction, the planar direction having a first axis parallel with the longitudinal axis 6X of the manifold 600. The planar direction has a second axis, perpendicular to the longitudinal axis, and in this embodiment, the second axis is in a direction shown by arrow 6Y and is parallel to an axis of the sectional view. In this embodiment the second axis is perpendicular to a transverse axis 6Z of the ribbon cable, the transverse axis passing through an axial centre-line of each of the optical fibres in the ribbon cable.

[0056] In an alternative embodiment, not shown in the Figures, the embodiment having a planar direction with a first and second axes similar to those described with reference to the embodiment 600, however in the alternative embodiment the second axis is at an angle other than 90 degrees to the transverse axis of the ribbon cable.