Abstract:
The invention relates to a fibre optic routing board for routing a plurality of fibre optic cables. The fibre optic routing board is provided with one or more optical conductors disposed between a first lower laminate layer and a first upper laminate layer, the one or more optical conductors being connected to at least one of the optical fibres in the plurality of fibre optic cables, wherein at least one of the first lower laminate layer or the first upper laminate layer is so constructed that it attaches at least one of a jacket over a first. Advantageously, the fibre optic routing board additionally comprises a second laminate layer positioned between the first upper or lower laminate layer and the optical conductors. The use of a two layer laminate allows each of the laminate layers to have different properties. Thus one layer might reduce transverse stresses on the connecting element and enclosed optical fibre whilst another layer might reduce longitudinal stresses on the connecting element and enclosed optical fibre.

Description:
FIELD OF THE INVENTION 
     The invention relates to a fibre optic routing system for routing a plurality of fibre optic cables. 
     PRIOR ART 
     Routing boards are known, for example, from U.S. Pat. No. 5,204,925 (Bonanni et al.), assigned to AT&amp;T Bell Laboratories, Murray Hill, N.J. It is known that optical fibres incorporated into such routing boards are very fragile and can be broken easily when put under stress. One weak link in such routing boards is the connection at the edge of the routing boards where the optical fibres are connected to the outside world. The connecting element is often placed under both lateral and transverse stresses and thus may be easily damaged. 
     From pending U.S. Ser. No. 08/880,965 filed Jun. 23, 1997 (Schricker) a laminate for use in opto-electronic devices is known which is compressible and also resistant to mechanical stresses. The use of the taught laminate for a routing board connecting element is, however, not disclosed in this patent. 
     Connectors for attachment to optical fibres are known from U.S. Pat. No. 4,678,264 (Bowen et al.) assigned to AMP Inc. and from U.S. Pat. No. 4,998,796 (Bonanni et al.) assigned to AT&amp;T Bell Laboratories. Neither of these document disclose, however, a connection to a routing board. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to improve the mechanical connection between a fibre optic routing board and a fibre optic cable. 
     A further object of the invention is to protect the optical fibres in the routing board from mechanical stress. 
     These and other objects of the invention are achieved by providing a fibre optic routing system with one or more optical conductors disposed between a first lower laminate layer and a first upper laminate layer, the one or more optical conductors being connected to at least one of the optical fibres in the plurality of fibre optic cables, wherein at least one of the first lower laminate layer or the first upper laminate layer is so constructed that it attaches at least one of a jacket over a first. By means of this construction, a mechanically strong bond is achieved between the laminate of the fibre optic routing board and the jacket of the fibre optic cable which reduces the risk that the fibre optic cable becomes separated from the fibre optic routing board when transverse or longitudinal stresses are applied to the fibre optic cable or the routing board. For the strongest joint, the jacket is preferably attached to both the first lower laminate layer and the first upper laminate layer. 
     Advantageously, the fibre optic routing board additionally comprises a second laminate layer positioned between the first upper or lower laminate layer and the optical conductors. The use of a two layer laminate allows each of the laminate layers to have different properties. Thus one layer might reduce transverse stresses on the connecting element and enclosed optical fibre whilst another layer might reduce longitudinal stresses on the connecting element and enclosed optical fibre. 
     In one embodiment of the invention, the jacket is attached to said second laminate layer over a second distance, thus additionally providing a mechanically strong bond between the fibre optic cable and the second laminate layer. 
     In another embodiment of the invention, an extension extends from the edge of said second laminate layer to a third distance within said jacket tube. This construction allows the second lamiante to be used to buffer the optical fibres within the fibre optic cable. It substantially improves the strength of the connection between the fibre optic cable and the fibre optic routing board since part of the routing board becomes part of the fibre optic cable. 
     The fibre optic cable has preferably reinforcement which is attached to said first upper laminate layer and/or said first lower laminate layer over a fifth distance and said second laminate layer over a sixth distance. This further improves the mechanical strength of the connection between the routing board and the fibre optic cable. 
     Preferably the fibre optic cable includes a buffering layer positioned between the reinforcement tube and the at least one of said optical conductors for buffering the optical conductors within the fibre optic cable. 
     In a preferred embodiment of the invention the first upper laminate layer and/or the first lower laminate layer and/or the second laminate layer comprise at least a first compressible layer and/or a mechanically resistant layer. The compressible layer is used to to improve the crush resistance of the routing board whilst the mechanically resistant layer improves the tolerance of the routing board to tensile forces. Preferably the compressible layer is made from expanded polytetrafluoroethylene (PTFE), foamed polyurethane, silicones and foamed polyethylene and the mechanically resistant layer is made from expanded PTFE, polyester, polyamide, or polyimide. 
     In a further embodiment of the invention a compressible layer is provided between the one or more optical conductors in order to protect the optical fibre conductors. 
     In one aspect, the routing system is a fibre optic routing system for routing a plurality of fibre optic cables comprising: 
     a plurality of fibre optic cable, each having at least one optical fibre surrounded by ajacket; and 
     a routing board with a first lower laminate layer situated below a first upper laminate layer, one or more optical conductors disposed between said first lower laminate layer and said first upper laminate layer, the one or more optical conductors being connected to at least one of the optical fibres in one of the plurality of fibre optic cables, wherein at least one of said first lower laminate layer or said first upper laminate layer is so constructed that it attaches at least one of the jacket over a first distance surrounding at least one of said optical fibres. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 a  &amp;  1   b  show perspective views of a fibre optic routing board according to the invention. 
     FIG. 2 shows a ruggedised connecting element between a fibre optic ribbon cable and a fibre optic routing board according to one embodiment of the invention. 
     FIG. 3 shows a ruggedised connecting element between a fibre optic ribbon cable and a fibre optic routing board according to a second embodiment of the invention. 
     FIGS. 4 a  &amp;  4   b  show a cross-sectional view through  4   a — 4   a  and  4   b — 4   b  of the fibre optic routing board of FIG. 1 a  and  1   b  respectively. 
     FIG. 5 shows a laminate which may be used as a laminate layer in the fibre optic routing board of the invention. 
     FIG. 6 shows a compressible layer positioned between the optical conductors on the routing board. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 a ,  1   b ,  4   a  and  4   b  show a routing board  5  having a plurality of incoming fibre optic cables  12 . Each fibre optic cable  12  has at least one optical fibre  11  positioned within it. The plurality of fibre optic conductors  10  are embedded within a first laminate layer  20  and a second laminate layer  50 . The routing board  5  is used for routing fibre optic conductors  10  between the optical fibres  11  in the fibre optic cables  12  and/or circuit packs (not shown) containing semiconductor components (not shown) and is described, for example, in U.S. Pat. No. 5,204,925 (Bonanni et al.), assigned to AT&amp;T Bell Laboratories, Murray Hill, N.J. 
     The first laminate layer  20  is preferably made from two polymer layers  22  and  26  laminated together as is shown in FIG. 5. A first one  22  of the two polymer layers is preferably a compressible polymer layer such as an expanded fluoroploymer. The first polymer layer  22  serves to buffer the fibre optic conductors  10  from damage caused by external forces on the surface of the routing board  5 . Most preferably the first polymer layer  22  is made from expanded polytetrafluoroethylene (ePTFE). In the preferred embodiment of the invention, the ePTFE has a density between 0.6 g/cm 3  and 1.8 g/cm 3  and thus a porosity between 18% and 73%. The expanded PTFE used is preferably that disclosed and described in U.S. Pat. No. 3,953,566, U.S. Pat. No. 3,962,153, U.S. Pat. No. 4,096,227 and U.S. Pat. No. 4,187,390. 
     The second one  26  of the two polymer layers is preferably a polymer which is chosen to provide the routing board  5  with high mechanical strength to resist damage to the enclosed fibre optic conductors  10  due to mechanical stress on the routing board  5 . Such mechanical stress may be caused by longitudinal forces exerted on the laminate by external influences. In order to provide sufficient mechanical strength, the second laminate layer  50  needs to have a high tensile strength. A tensile strength of 8000-15000 psi, preferably 12000 psi, is sufficient to provide adequate mechanical protection. A suitable polymer for use has been found to be polyester. However, other polymers, such as expanded PTFE, polyamide and polyimide, having the required properties can be also used. 
     The first polymer layer  22  and the second polymer layer  26  are laminated together by coating the first polymer layer  22  with a thermoplastic adhesive  24  and applying pressure and heat to the laminate. Suitable thermoplastic adhesives  24  can be selected from the group of adhesives containing polyester-based adhesives, polyurethane adhesives, fluorinated ethylene-propylene copolymers (FEP) adhesives, and perfluoroalkyl ethers of PTFE polymers. The temperature and pressure which have to be applied depend on the composition of the thermoplastic adhesives. 
     Alternatively, a pressure sensitive adhesive tape  24  could be used to laminate the first polymer layer  22  to the second polymer layer  26 . Examples of such tapes are manufactured by the 3M Corp. of St. Paul, Minn., and are made from a modified acrylic adhesive. They are sold under the brand name SCOTCH™. Alternatively silicone or rubber based adhesives may be used. In this method, a pressure-sensitive adhesive tape  24  is placed on one side of the first polymer layer  22 . On the pressure-sensitive adhesive tape  24 , the second polymer layer  26  is placed. Pressure is then applied to the surface of the second polymer layer  26  and the first polymer layer  22  and the first laminate layer  20  then become laminated together. 
     The manufacture of the first laminate layer  20  for the routing board  5  is described in more detail in co-pending U.S. Ser. No. 08/880,968 to the inventor herein, filed Jun. 23, 1997, incorporated by reference. 
     The second laminate layer  50  can either be constructed from two polymer layers as described above and depicted in FIG. 5 or it may merely consist of a single polymer layer which imparts high mechanical strength to the routing board  5 . In this case a polymer such as polyester would be chosen. As shown in FIG. 1, the area of the second laminate layer  50  is preferably greater than that of the first laminate layer  20  so as to protect the first laminate layer  20  from mechanical damage. 
     The connection of the fibre optic ribbon cables  12  to the routing board  5  will now be described. 
     A first embodiment of the invention is depicted in FIG. 1 a  and FIG. 4 a . It is shown in a longitudinal sectional view in FIG.  2 . In this embodiment of the invention, the optical conductors  10  from the conventional fibre optic cable  12  such as the FLEX-LITE™ fibre optic ribbon cable supplied by W. L. Gore &amp; Associates are to be connected to the routing board  5 . The fibre optic cable  12  includes a buffering layer  35  placed in immediate contact with the plurality of optical conductors  10  within the fibre optic cable  12  and a reinforcement layer  30  placed between the buffering layer  35  and an outer jacket  40 . The reinforcement  30  is used to provide mechanical strength for the fibre optic cable  12  and can be made of any material with high tensile strength. In the preferred embodiment of the invention, it is preferably made of aramide fibres, for example KEVLAR® braid or fibre. Alternatively it could be made from thin glass fibres, polymer coated thin glass fibres, RASTEX® fibres made from ePTFE and obtainable from by W. L. Gore &amp; Associates or DYNAR® fibres. The buffering layer  35  buffers the optical conductors  10  from the outside environment and is preferably made from expanded PTFE. 
     The outer jacket  40  serves to protect the reinforcing tube  30  from damage. The outer jacket can be made of any material suitable for such purpose such as polyvinylchloride (PVC), expanded PTFE such as GORE-TEX® laminate available from W. L. Gore &amp; Associates, PTFE, fluorinated ethylene/propylene(FEP), a co-polymer of TFE and perfluoropropylvinyletlier(PFA), PVDF, polyester, polyurethane or polyamide. 
     Referring to FIGS. 1 a  and  2 , to connect the fibre optic cable  12  to the routing board  5 , part of the outer jacket  40  is removed over at least a distance A to expose the reinforcement  30  over a distance J and part of the reinforcement  30  is also removed to expose the buffering layer  35  over a distance B. Naked, i.e. unprotected, optical fibres  11  protrude out of the end of the fibre optic cable  12 . The outer jacket  40  remains attached to the fibre optic cable  12  over a distance H. The fibre optic cable  12  is then laid on the bottom half of a routing board  5  which comprises the bottom second laminate layer  50   a  and the bottom first laminate layer  20   a  such that the outer jacket  40  extends at distance C over the bottom second laminate layer  50   a  and a distance D over the bottom first laminate layer  20   a  as is shown on FIG. 1 a . After placement of the fibre optic cable  12  on the routing board  5 , the fibre optic conductors  10  extending therefrom are routed to the required positions on the routing board  5 . These position may be to other fibre optic cables  12  or to opto-electronic components (not shown). Preferably the upper side of the bottom first laminate layer  20   a  is provided with fixation means in order to secure the fibre optic cable  12  and the fibre optic conductors  10  protruding therefrom during the manufacturing process. 
     The fixation means used may be a pressure sensitive adhesive or other adhesives such as those listed above for laminating the polymer layers  22  and  24  in the first laminate layer  20  or the second laminate layer  50 . 
     After all of the required fibre optic cables  12  are connected to and placed on the routing board  5  and the fibre optic conductors  10  are placed in their required positions, the top first laminate layer  20   b  is placed over the fibre optic cables  12  and fibre optic conductors  10  directly above the bottom first laminate layer  20   a . The bottom side of the top first laminate layer  20   b  is coated with an adhesive, similar to those listed above which bonds with the top side of the bottom first laminate layer  20   a  and with the outer jacket  40 , the reinforcement  30 , and the buffering layer  35  of the fibre optic cable  12 . The top second laminate layer  50   b  is then placed over the top first laminate layer  20   b  such that it is directly above the bottom second laminate layer  50   a . The bottom side of the top second laminate layer  50   b  is coated with an adhesive such that it adheres to the top side of the top first laminate layer  20   b , the top side of the bottom laminate layer  50   a  and the outerjacket  40  of the fibre optic cable  12 . 
     After any required curing treatment for the adhesives is carried out, an extremely strong connection is made between the fibre optic cable  12 , the fibre optic conductors  10  and the routing board  5  such that the routing board  5  and attached fibre optic cables  12  can withstand high tensile forces. 
     A second embodiment of the invention is shown in FIG. 1 b  and FIG. 4 b . It is shown as a longitudinal section in FIG.  3 . In this embodiment of the invention, conventional fibre optic ribbon cable is not used as the fibre optic cable  12 . Instead the fibre optic cable  12  is formed by an extension  80  from a main portion  75  of the first laminate layer  20  as a protrusion or finger from the edge  6  of the routing board  5 . This can be clearly seen in FIG. 3 by comparison with FIG.  2 . 
     In FIG. 3 it is shown that part of the first laminate layer  20  extends beyond a main body  75  of the first laminate layer  20  and beyond the edge of the routing board  5 . The extension  80  includes the fibre optic conductors  10  sandwiched by the first laminmate layer  20 . A reinforcement  30  is placed over the first laminate layer  20  over a distance F. The reinforcement  30  is disposed between an outer jacket  40  and the first laminate layer  20  over a distance E. In this embodiment of the invention, the extension  80  of the first laminate layer  20  within the fibre optic cable  12  buffers the fibre optic conductors  10  and there is thus no need for a separate buffering layer  35  as known from the first embodiment of the invention (FIG.  2 ). The outer jacket  40  and the reinforcement  30  according to this embodiment of the invention can be made from the same materials as those used in constructing the first embodiment of this invention. 
     Manufacture of the second embodiment of the invention is carried out as follows. In a first step, a first bottom and top first laminate layer  20   a ,  20   b  are cut to the required dimensions for the main body  75  of the routing board  5  and the extension  80 . The reinforcement is attached respectively to the bottom side of the extension  80  of the bottom first laminate layer  20   a  and the top side of the extension  80  of the top first laminate layer  20   b . In particular it should be noted that both the bottom first laminate layer  20   a  and the top first laminate layer  20   b  must be matched in form with extensions  80  of similar length. The main body  75  bottom first laminate layer  20   a  is placed on the bottom second laminate layer  50  such that the bottom second laminate layer  50   a  completely covers the main body  75  of the bottom first laminate layer  20   a  with only the extensions  80  extending beyond the edge  6  of the bottom second laminate layer  20   a.    
     The fibre optic conductors  10  are laid on the surface of the bottom first laminate layer  20   a  in the required routing configuration. The top first laminate layer  20   b  is then placed on the fibre optic conductors  10  exactly over the planar area of the bottom first laminate layer  20   a  such that the fibre optic conductors  10  are enclosed by the top first laminate layer  20   b  and the bottom first laminate layer  20   a.    
     The reinforcement  30  and the outer jacket  40  are then placed over the extensions  80 . Finally the top and bottom second laminate layers  50   a  and  50   b  are put in position over each other as described above. Fixation means such as adhesives are used to ensure bonding between the various components of the routing board  5  and the fibre optic cables  12 . After curing of the adhesives, an extremely strong bond is formed between the extensions  80  and the routing board  5  which protects the fibre optic conductors  10  from damage. 
     In the above description, it has been assumed that the fibre optic cables  12  are ribbon cables. However, round fibre optic cables could also be used. 
     In an additional embodiment of the invention as shown in FIG. 6, a compressible layer  18  is placed between the optical conductors  10  within the routing board  5 . This compressible layer  18  is made from the same materials as the polymer layer  22  and most preferably from expanded PTFE. This compressible layer serves to protect the optical conductors  10  from damaging each other and additionally serves to minimise any damage to the optical conductors  10  from mechanical damage from external influences. It is furthermore possible to use several compressible layers  18  between the optical conductors  10 . 
     Although a few exemplary embodiments of the present invention have been described in detail above, those skilled in the art readily appreciate that many modifications arc possible without materially departing from the novel teachings and advantages which are described herein. Accordingly, all such modifications are intended to be included within the scope of the present invention, as defined by the following claims.