Abstract:
The present application discloses embodiments of a dropcable structure that includes one or more carbon nano tube (CNT) wires and one or more bores, the or each bore being adapted to receive a further cable installed by a blown cable installation process an electrical power supply.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is a National Phase entry of PCT Application No. PCT/GB2013/000179, filed Apr. 23, 2013, which claims priority to EP 12250100.0, filed Apr. 23, 2012, the contents of which are incorporated herein by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments relate to a dropcable and in particular to a dropcable for use in connecting domestic or commercial premises to a communications networks, for example via a telephone pole. 
       BACKGROUND 
       [0003]    Asymmetric digital subscriber line (ADSL) systems enable data to be transmitted over a pair of metallic twisted pair (usually copper) wires to customer premises. It is thought that the realistic maximum transmission performance that is likely to be obtained with modern variants of ADSL is a download data rate of 24 Mbps and an upload speed of about 3 Mbps at the expected nominal distance of a customer premises from an exchange in a telecommunications network. Such data rates are dependent on the length of the metallic twisted pair from the customer premises to the telephone exchange and thus many customers will receive services at significantly lower data rates. 
         [0004]    To improve data rates optical fiber has been installed into the access network. The greatest data rates are likely to be provided using fiber to the premises (FTTP) networks, such as passive optical networks (PONS) but there is a significant cost involved in providing fiber directly to customer premises. Fiber to the cabinet (FTTCab) and Fiber to the Distribution Point {FTTDP) networks are known to provide an attractive solution to providing customers with high data rate services without requiring as much investment as FTTP networks. Typically in FTTCab networks, very high bit-rate digital subscriber line (VDSL) systems are used to provide download data rates of 40 Mbps and higher over the metallic twisted pair cables. It is believed that improvements to VDSL systems may provide download data rates in excess of 100 Mbps. FTTP networks can provide almost unlimited bandwidth to customers and it is likely that commercial considerations rather than technical issues will limit that data rates that will be supplied to customers. One particular problem is the cost of installing optical fiber into customer premises. One approach is to install a hollow tube from a network node to the customer premises and to then install a bundle of optical fiber into the tube using a source of compressed. air and by pushing the bundle of fibers. 
         [0005]    Such blown fiber (sometimes referred to as blown cable) techniques were first described in EP-B-108 590. An example of the type of tubing used for blown fiber installation is described in EP-8-432 171; EP-B-521 710 discloses a cable structure suitable for a blown fiber installation. and EP-8-1 015 928 discloses a cable blowing apparatus. 
         [0006]    According to a first embodiment, there is provided a dropcable for use in a communications network, the dropcable comprising one or more carbon nano tube (CNT) wires and one or more bores, the or each bore being adapted to receive a further cable installed by a blown cable installation process. in one embodiment, the or each bore comprises an inner layer comprising materials which reduce the coefficient of friction during the installation of a further cable installed by a blown cable installation process. 
         [0007]    The dropcable may comprise one or more pairs of CNT wires configured to conduct an electrical signal, The electrical signal may comprise a data signal or a power signal. The dropcable may comprise one or more CNT wires configured to act as a reinforcing element. The CNT wires may comprise an external coating. The dropcable may comprise two bores adapted to receive a further cable installed by a blown cable installation process. 
         [0008]    In an embodiment, the dropcable is adapted to connect a node of a communications network to a customer premises. Furthermore, the dropcable may be adapted to be connected to the customer premises via a telephone pole. 
         [0009]    Such a dropcable may provide significant operational advantages to a network operator. A dropcable according to embodiments will support all of the different network architectures discussed above. It can be used to provide conventional PSTN/DSL services using the CNT wires to carry electrical telephony and data signals. If a customer elects to upgrade to FTTC-based, services then the data can still be sent over a pair of CNT wires. A further pair of CNT wires can be used to back-power FTTC equipment from the customer premises. If a customer decides to receive services delivered over FTTP then as the blowing tube is already present then the upgrade can be provided more readily as there is no need to install a dropcable comprising a blowing tube. Furthermore, if a customer decides to move back to conventional PSTN/DSL services then this can be achieved without needing to modify the network infrastructure further. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0011]      FIG. 1  shows a schematic depiction of a cable according to a first embodiment. 
           [0012]      FIGS. 2 to 4  show a schematic depiction of a variant of the cable shown in  FIG. 1 . 
           [0013]      FIG. 5  shows a schematic depiction of a cable according to a second embodiment. 
           [0014]      FIG. 6  shows a schematic depiction of a variant of the cable shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a schematic depiction of a cable  100  according to a first embodiment. The cable  100  comprises a body region  110  which has an annular shape such that it defines a central bore  120 . Contained within the body region  110  are a plurality of carbon nanotube (CNT) wires.  FIG. 1  shows that the cable comprises 4 CNT wires which are, for example, arranged in 2 pairs of CNT wires. It should be understood that the cable might comprise a greater number of CNT wires. Carbon nanotubes are an allotrope of carbon and they have a substantially cylindrical form. It is known to form wires from CNTs to take advantage of the electrical characteristics of CNTs such that electrical currents can be passed down the wires. See, for example, U.S. Pat. No. 7,993,620, W02004/043858 and Zhao et al “ Iodine doped carbon nanotube cables exceeding specific electrical conductivity of metals ”. Scientific Reports, |1:83| DO|: 10.1038/srep00083. 
         [0016]    It has been demonstrated that carbon nanotubes can be fabricated in large quantities and with specific diameters and chirality that means that they have the properties of metallic conductors, It is thought that significant advantages in electrical and physical characteristics can be realized for wires manufactured from such CNTs. For example, it is theoretically predicted that such CNT wires will have lower resistivity than copper or silver conductors and that they will not be subject to the skin effect that is present in copper conductors, which leads to a decreased performance as the frequency of an AC current passed through them increases. In addition it has been demonstrated that CNTs can be used for data transmission. Physically, CNT wires have been demonstrated to be highly flexible and extremely strong and therefore suited to fabrication into very fine but robust structures. 
         [0017]    The cable  100  can be used as a drop cable which can be used in a FTTP network, a MC network or a conventional PSTN network. If the network is a conventional PSTN network or a FTTC network then one (or more) of the pairs of CNT wires can be used to carry the electrical signals that are sent from the network to the customer premises (and also from the customer premises back to the communications network). If the network is a FTTP network then an optical fiber bundle can be blown through the bore  120  to provide the connection from the network to the customer premises. 
         [0018]    Regardless of the type of network that the cable is connected to, one or more of the pairs of CNT Wires may be used to provide an electrical power signal. This may be used to provide power from the customer premises to a network node such that optoelectronic equipment in the network can be powered. Alternatively, power may be supplied from a network node to power the customer premises equipment. Conventional telephone handsets can be powered by electrical signals sent over the PSTN so that even if electrical power is lost at the customer premises then it is still possible to provide telephony services. Providing back-up power for FTTP networks is conventionally implemented by installing batteries within the customer premises. The different CNT wires within the cable will be colored according to a predetermined color scheme such that they can be identified by an engineer. If required, the CNT wires may be coated with one or more outer layers that provides mechanical protection and/or electrical insulation. The color identification scheme may be applied to, or incorporated as a part of the outer layer(s). The CNT wires may be formed in the cable such that they are parallel to blowing bores but it is preferred in some embodiments that the CNT wires are stranded around the blowing bores. The stranding of the CNT wires provides a degree of strain relief When the cable experiences a longitudinal strain. 
         [0019]    By controlling the chirality of the CNTs it is possible to determine the characteristics of the CNT wires that are thereby formed.  FIG. 2  shows a variation of the cable  100  described above with respect to  FIG. 1  in which the cable comprises one pair of CNT wires  132  which have been configured to have improved electrical characteristics and one pair of CNT wires which have been configured to have improved mechanical characteristics, An additional color scheme or identifier may be provided such that the CNT wires configured to have improved electrical characteristics can be distinguished from the CNT wires configured to have improved mechanical characteristics. It will be understood that the cable shown in  FIG. 2  may comprise a greater number of CNT wires (or pairs of CNT wires) than those shown. 
         [0020]      FIG. 3  shows a further variation of the cable  100  described above with respect to  FIG. 1 . The blowing bore  120  is defined by an inner layer  122  which is received upon an outer layer  124 , The inner layer  122  preferably comprises materials which give a low friction during the blown installation of a cable or fiber bundle. Arranged around the outer layer  124  is the cable body  112 , within which is received a plurality of CNT wires  130 . The cable body is surrounded by a tape or layer  114 , which protects the cable body from water ingress into the cable. An external jacket  116  is located around the layer  114  to protect the cable from abrasion and/or mechanical damage. 
         [0021]      FIG. 4  shows a yet further variation of the cable  100  described above with respect to  FIG. 1 . In a similar manner to the cable variant described above with reference to  FIG. 3 , the blowing bore  120  is defined, by an inner layer  122  which is received upon an outer layer  124 . The CNT wires  130  are arranged around the outer layer  124  and are held in place by water barrier layer  114 . The interstices between the CNT wires are preferably filled to prevent longitudinal water protection, for example using a thixotropic gel. The water barrier layer  114  is covered with an external jacket  116 . 
         [0022]      FIG. 5  shows a schematic depiction of a cable  100 ′ according to a second embodiment in which the cable comprises two bores  120  into which a cable or fiber bundle may be blown. Each of the bores  120  is defined by an inner layer  122  which is received upon an outer layer  124 . Again, the inner layer  122  can comprise materials which give a low friction during the blown installation of a cable or fiber bundle. The cable  100 ′ has a cross-section which is substantially lozenge-shaped. In addition to the two bores the cable  100 ′ comprises a plurality of insulated CNT wires  136 . These CNT wires comprise external insulation  138  applied around the exterior of the CNT wires  130 . A first sub-set of the plurality of insulated CNT wires  136  may be associated with a first blowing bore and a second sub-set of the plurality of insulated CNT wires  136  may be associated with the other blowing bore.  FIG. 6  shows a variation of the cable  100 ′ described above with respect to  FIG. 5 ; cable  100 ″ has a cross-section which is normally referred to as ‘figure of eight’, with two lobes being connected by a narrower central section. As before, the cable  100 ″ comprises two blowing bores  120  and a plurality of insulated CNT wires  136 , such that a first sub-set of the plurality of insulated CNT wires  136  may be associated with a first blowing bore and a second sub-set of the plurality of insulated CNT wires  136  may be associated with the other blowing bore. 
         [0023]    It will be readily and immediately apparent to those skilled in the art of cable design and manufacture that a great number of variants of these cables may be produced without departing from the teachings of embodiments of the present invention. It will be understood that additional cable elements and materials that are not described above or shown in  FIGS. 1-6  may be added into a cable according to various embodiments. 
         [0024]    One of the limitations of a dropcable is that they are normally installed from telegraph poles to customer premises and thus are at risk of being struck by vehicles if the cables. For this reason, dropwires and droprables are normally designed to break in the event of a vehicle strike to minimize the risk that the telegraph pole supporting the dropcable is damaged or broken. The person skilled in the art of cable design and manufacture will be aware of this design limitation and will be able to produce an appropriate dropcable design which complies with it. 
         [0025]    Another known allotrope of carbon is graphene. It is known to spin graphene oxide flakes into fibers several meters in length (see Z Xu &amp; C Gao, ‘ Graphene chiral liquid crystals and macroscopic assembled fibres ’ Nature Communications 2, 571 (2011)). These graphene fibers are electrically conductive and could be used in place of CNT wires in cables according to embodiments. 
         [0026]    In summary, embodiments relate to a new and inventive cable structure which comprises: a bore for receiving a blown fiber cable or bundle; one or more carbon nano tube wires for transmitting data signals; and/or one or more carbon nano tube wires for transmitting an electrical power supply.