FIELD OF THE INVENTION 
   The present invention relates to optical fibres support and retaining devices, and in particular, manifolds for optical fibres. 
   SUMMARY OF THE INVENTION 
   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. 
   It is known to provide an optical fibre manifold arranged to spread optical fibres from a single dimensional ribbon array to a two-dimensional block array, such as is shown in JP-A-10,170,735 (Nippon Telegraph &amp; Telephone Corporation). However, a problem exists in manifolds where individual optical fibres change direction rapidly and this is known as “microbending”. In the Nippon Telegraph document, the optical fibres change direction quite sharply so that there is a change in direction in two dimensions, that is, at right angles to the ribbon plane and in the ribbon plane, causing a measurable twisting in the fibres. The spacing of the fibres overall is compressed in the Nippon Telegraph document. In a further document, namely JP-A-09,197,145 (Tatsuta Electric Wire &amp; Cable), the problem of degradation of signal is mentioned. However, the solution proposed is unclear but seems to reside in tightly bundling fibres from the ribbon array into a tight circular array, requiring again a sharp change of direction of the fibres from a single transverse plane in both directions towards the centre of the ribbon axis in one dimension, parallel with the transverse plane and also in a direction at right angles to the transverse ribbon plane. 
   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, adjacent fibres in the ribbon array being spaced apart a first distance in a transverse direction characterised in that the same adjacent fibres remain the same first distance apart in the transverse direction when in the block array although being spread apart to at least a second distance. 
   The resultant change in geometric alignment of the optical fibres in the manifold of the invention is that there is a minimum of angular displacement which reduces the signal degradation. 
   A benefit of the invention is that each of the optical fibres of the ribbon array are only deflected in a single planar direction. 
   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. 
   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. 
   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. 
   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. 
   Preferably an end of each of the flexible tubes is mounted to the block. 
   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. 
   Preferably the block array comprises holes through which the optical fibres may pass, arranged in rows. 
   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. 
   Preferably the manifold is symmetrical about an axial plane. 
   A benefit of this is that the number of different components that are required to be manufactured may be minimised. 
   Preferably the manifold is provided with a strain relief to ensure that the ribbon array is located securely to the manifold. 
   A benefit of the strain relief is that optical fibres within the manifold may remain in an unstressed condition. 
   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. 
   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 band strain while under tension. 
   A benefit of bend radius control is that a risk of damage to the optical fibre is reduced. 
   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. 
   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. 
   Preferably the sleeve is of sufficient length to cover the ribbon cable extending beyond the bond radius region. 
   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. 
   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. 
   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. 
   A benefit of this is that each of the optical fibres is routed through the manifold with no micro-bands that would cause damage to the optical fibres or reduce the transmission of light through the optical fibres. 
   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. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  is a perspective view of a first manifold according to the invention; 
       FIG. 2  is a perspective view of a block array of the manifold shown in  FIG. 1 ; 
       FIG. 3  is a diagrammatic end view of the block array shown in  FIG. 2  showing the layout of holes to receive tubes; 
       FIG. 4  is a longitudinal sectional view of part of the manifold of  FIG. 1 ; 
       FIG. 5  is a perspective view of a support block for use with the manifold shown in  FIG. 1 ; 
       FIG. 6  is a perspective view of a second manifold according to the invention; 
       FIG. 7  is a perspective sectional view of the second manifold; and 
       FIG. 8  is a further sectional view along a longitudinal axis of the second manifold. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   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. 
   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. 
   The elestomeric 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. 
     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. 
   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 nm and dimension c and d are each 6 mm and length of the housing is dimension a which is 25 mm. 
   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:—
 
 z=nx=y+x  
         where:—
           n is the number of rows in the block array   x is the pitch of the optical fibres in the ribbon army   y is the dimension parallel to a transverse plane of the ribbon array between the centres of n holes   z is the dimension parallel to a transverse plane of the ribbon array between the centres of adjacent holes in the same row.   
               

   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. 
   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  26  has a radiused edge facing the chamber  26  to minimise a risk of damage to the optical fibres. 
     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 bond 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. 
   In an alternative embodiment similar to that of manifold  1 , the support block is formed as part of the housing moulding. 
   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  6 P to spread the fibres to a two dimensional block array  664  at the exit from the manifold. The block array having a height  6 H and a width  6 W. The width  6 W being the same as a width  6 R of the ribbon cable. 
     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  6 A, 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  6 N 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  6 S 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 . 
   The housings  603  and  604  are provided with an exit bend radius  684  at the exit opening  662 . A dimension  8 N 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  6 L 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. 
   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  6 X 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. 
   From  FIG. 8 , it can be seen that each optical fibre is displaced in a smooth curve at  8 C 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  6 X 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  6 Y and is parallel to an axis of the sectional view. In this embodiment the second axis is perpendicular to a transverse axis  6 Z of the ribbon cable, the transverse axis passing through an axial centre-line of each of the optical fibres in the ribbon cable. 
   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.
An optical fiber manifold arrange to orientate a plurality of optical fibers from a single dimensional ribbon array to a two dimensional block array, wherein the fiber spacing (X) in the block array is the same as the fiber spacing in the ribbon array.