Abstract:
A hybrid data communications cable includes optical fibers and insulated electrical conductors. The cable includes an elongated filler member having a central portion, walls extending radially from the central portion and a conduit running the length of the filler member. The optical fibers are enclosed within the conduit, and at least one insulated electrical conductor is separated from another insulated electrical conductor by one or more walls of the filler member. The cable further includes a jacket that encloses the filler member and the insulated electrical conductors.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to hybrid cables having both optical and electrical transmission media. 
     2. Discussion 
     Fiber optic cables are increasingly used to transmit video, voice, and data. Optical fiber offers advantages of small size, lightweight, large bandwidth and high transmission data rates. Unlike traditional metal wire, optical fiber is immune to electromagnetic interference, which adversely affects transmission quality. 
     Although optical fiber often performs better than traditional metallic media, the telecommunications industry continues to purchase metal wire for many reasons. For example, existing telecommunications hardware is often incapable of sending and receiving optical transmissions without costly modification. Furthermore, even as the telecommunication industry upgrades to equipment that can send and receive optical signals, it continues to use hardware that depends on metal wire for signal transmission. 
     Consequently, there is a need for cables that can transmit both electrical and optical signals. 
     SUMMARY OF THE INVENTION 
     The present invention provides a novel hybrid data communications cable that can be efficiently manufactured without compromising the quality of electrical and optical signals transmitted by the cable. 
     The hybrid data communications cable includes a filler member having a longitudinal axis, and a conduit embedded in the filler member approximately parallel to the longitudinal axis. The filler member includes a central portion and walls extending radially from the central portion. The filler member, which is typically reinforced with elongated strength members or fillers, includes one or more optical fibers. The cable also includes a first and second group of insulated conductors that are separated from each other by at least one of the walls. Furthermore, the cable includes a jacket for housing the elongated filler member and the insulated electrical conductors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a cross-sectional view of one embodiment of a hybrid cable. 
     FIG. 2 illustrates a cross-sectional view of another embodiment of a hybrid cable. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a cross-section of one embodiment of a hybrid cable  10 . The cable  10  comprises a filler member  14  that extends along a longitudinal axis of the cable  10 . The filler member  14  includes a central portion  18 , and walls  22  extending radially from the central portion  18 . The filler member  14  may be oriented such that the walls  22  remain in their respective planes along the longitudinal axis. Alternatively, the filler  14  member is either helically or SZ twisted along its longitudinal axis, which facilitates mid-span access of the cable  10 . The filler member  14  is typically made from one or more thermoplastic materials. Useful thermoplastics include, but are not limited to polyethylene, polypropylene, polyester, polystyrene, poly(ethylene terephthalate), poly(vinyl fluoride), poly(vinyl chloride), halogenated and non-halogenated poly(vinylidenes), polyamide, and polytetrafluoroethylene. Other useful filler member  14  materials include polymeric elastomers, cross-linked polymers, copolymers, ultraviolet light curable polymers, and the like. The filler member  14  may be formed by extrusion, pultrusion, or cut from solid polymer. 
     The filler member  14  may also include elongated strength members or discrete reinforcing particles. Strength members can include metal rods, or continuous fiber bundles of glass, nylon, graphite, oriented, liquid crystalline polymers or aramid (e.g. KEVLAR). In one embodiment, the filler member  14  may be extruded over one or more aramid fiber strength members such that the strength members extend along the longitudinal axis of the cable  10  within the central portion  18  or the walls  22  of the filler member  14 . In another embodiment, the strength members may be metal rods extending radially outward from the central portion  18  within the walls  22  of the filler member  14 . The filler member  14  may also comprise extruded oriented liquid crystalline polymers. Discrete reinforcing particles may also be used to add strength to the filler member  14 . These particles are typically dispersed throughout the filler member  14 . Useful reinforcing particles include metal shavings, glass fibers, aramid fibers, graphite fibers, carbon black, clays, and nucleators such as talc or sodium benzoate. 
     As shown in FIG. 1, a conduit  26  extends along the longitudinal axis of the cable  10  within the central portion  18  of the filler member  14 . The conduit  26  is generally cylindrical and is defined by a cylindrical surface  30 . Other conduits (not shown) may extend down the length of one of the walls  22 , generally parallel to the longitudinal axis of the cable. 
     The hybrid cable  10  also includes one or more optical fibers  34  enclosed in the conduit  26 . The optical fibers  34  may be loose fibers, tight buffered fibers, or fiber ribbons, and typically extend down the entire length of the filler member  14 . The optical fibers  34  may be single-mode, multi-mode or a mixture of optical fibers (glass or plastic) depending on their intended use and should have a protective coating. Furthermore, the optical fibers  34  may be color-coded for identification purposes. 
     The size and shape of the conduit  26  can vary depending on the size, number and shape of the optical fibers  34 . The conduit  26  should provide the optical fibers  34  with enough space to allow the cable  10  to bend without placing excessive stress on the optical fibers  34 . The inner surface  30  of the conduit  26  may contact the optical fibers  34  if the filler member  14  and the optical fibers  34  have similar coefficients of thermal expansion. If the coefficients of thermal expansion of the filler member  14  and the optical fibers  34  are dissimilar, a buffering material may be needed to separate the optical fibers  34  from the filler member  14  to avoid damage to the optical fibers  34 . Suitable materials include, but are not limited to powder, gel and aramid fibers. 
     The optical fibers  34  can be placed in the conduit  26  in several ways. For example, the filler member  14  may be extruded over the optical fibers  34  so that the conduit  26  surrounds the optical fibers  34 . Alternatively, the optical fibers  34  may be pulled through the conduit  26  after the filler member  14  is formed, or the optical fibers  34  may be placed in the conduit  26  through a slit in the wall of the conduit  26  that is later sealed using adhesives, welding or other suitable sealing techniques. 
     As shown in FIG. 1, the cable  10  also includes insulated conductors  38 . The conductors  38  are typically single or multi-stranded copper wires insulated with one or more polymeric layers. Useful polymeric insulations include thermoset, thermoplastic, and ultraviolet light curable polymers. Examples of these include, but are not limited to polyamide, polyamideimide, polyethylene, polyester, polyaryl sulfone, polyacrylates and the like. 
     The conductors  38  can be arranged in several configurations. For example, FIG. 1 shows twisted pairs  42  of insulated conductors  38  separated by the walls  22  of the filler member  14 . Each of the twisted pairs  42  is comprised of two insulated conductors  38 . The twisted pairs  42  are separated into zones  50 . Pairs of adjacent walls  22  and a portion of a cable jacket  50  define each of the zones  46 . In FIG. 1, there are four zones  46 , but the number of zones  46  can vary depending on the number of walls  22 . The walls  22  decrease cross talk between twisted pairs  42 . To further decrease cross talk, the walls  22  may be made of a semi-conductive filled or unfilled polymer. Useful semi-conductive filled polymers include polyethylene, polypropylene, polystyrene and the like containing conductive particles, such as carbon black, graphite fiber, barium ferrite, and metal flakes, fibers or powders. Other useful semi-conductive polymers include intrinsically conductive polymers such as polyacetylene and polyphtalocyanine doped with gallium or selenium. 
     The cable  10  shown in FIG. 1 has one twisted pair  42  in each of the zones  46 , but the zones may also contain many other arrangements of conductors. 
     FIG. 2 illustrates other possible arrangements of conductors within another hybrid cable  70 . For example, a first zone  74  has no conductors. A second zone  78  has a group of conductors comprised of four insulated conductors  82  twisted together to form a conductor bundle  86 . A third zone  90  contains two twisted pairs  94  of insulated conductors. A fourth zone  98  contains a twisted pair  102  and a conductor bundle  106 . A person of skill in the art will appreciate that many other arrangements are possible. The particular arrangement will depend on design criteria including signal to noise ratio and signal throughput. 
     Referring again to FIG. 1, the jacket  50 , which encloses the filler member  14  and the conductors  38 , is typically made of plastic material. Preferably, the plastic material is flame retardant. Suitable plastic materials include, but are not limited to polyethylene, polypropylene, polyvinyl chloride, or non-halogenated flame-retardant materials. The plastic material may be made and installed through any number of methods known in the art, including extrusion or tape wrapping. The jacket  46  may or may not contact the walls  22  along the length of cable  10 .