Abstract:
Micromodule cables include subunit, tether cables having both electrical conductors and optical fibers. The subunits can be stranded within the micromodule cable jacket so that the subunits can be accessed from the micromodule cable at various axial locations along the cable without using excessive force. Each subunit can include two electrical conductors so that more power can be provided to electrical devices connected to the subunit.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/US11/34315 filed Apr. 28, 2011, which claims the benefit of priority to U.S. Application No. 61/330,057, filed Apr. 30, 2010, both applications being incorporated herein by reference. 
         [0002]    This application is related to U.S. application Ser. No. 11/891,008, filed Aug. 8, 2007, now U.S. Pat. No. 7,627,218, and to PCT/US09/66401, filed Dec. 2, 2009, the entire contents of which are hereby incorporated by reference. 
     
    
     SUMMARY 
       [0003]    According to a first embodiment a micromodule cable comprises a cable jacket and at least three subunit cables surrounded by and in contact with the cable jacket and SZ stranded together. Each subunit cable comprises a subunit jacket having a cavity; a micromodule cable disposed within the subunit jacket, the micromodule cable comprising a plurality of optical fibers surrounded by a micromodule jacket; a longitudinally extending strength member disposed within the jacket; a first electrical conductor disposed within the jacket; and a second electrical conductor disposed within the jacket. 
         [0004]    The micromodule cable can be accessed by cutting the micromodule cable jacket at a first location; severing a first subunit cable at the first location; cutting the cable jacket at a second location a distance of at least 0.7 meter from the first location; and pulling the first subunit cable out of the cable jacket. The first subunit cable can then serve as a “tether” and provide electrical and optical data connectivity to a remote device located along the length of the micromodule cable. Each subunit cable can be accessed at a different axial location along the micromodule cable and connected to remote devices. Alternatively, multiple subunit cables can be accessed at the same location to connect to multiple devices. 
         [0005]    According to one aspect, each subunit includes a pair of electrical conductors so that additional power can be provided to remote devices. The micromodule cable, including the subunit cables, can be constructed of selected materials and in selected dimensions so that the micromodule cable passes selected burn and voltage requirements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system/assembly components and/or method steps, as appropriate, and in which: 
           [0007]      FIG. 1  is cross-sectional view of a hybrid subunit cable according to a first embodiment. 
           [0008]      FIG. 2  is cross-sectional view of a micromodule cable including multiple subunit cables as shown in  FIG. 1 . 
           [0009]      FIG. 3  illustrates a method of accessing the subunit cables within the micromodule cable of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  is a cross-sectional view of a subunit or “tether” cable  10  according to a present embodiment. The subunit cable, or simply “subunit”  10  includes a polymer cable jacket  20  surrounding a pair of insulated conductors  30 , and a micromodule cable, or simply “micromodule”  40 . The insulated conductors  30  each include a metallic conductor  32  surrounded by insulation  36 . The micromodule  40  includes a plurality of optical fibers  42  surrounded by a polymer jacket  46 . A tensile strength member  50 , such as one or more longitudinally extending aramid yarns, can be included in the cavity of the jacket  20 . The jackets  30 ,  46  can be formed primarily from polymer materials, and can be generally referred to as “polymeric.” In this specification, the term “polymer” includes materials such as, for example, copolymers, and polymer materials including additives such as fillers. 
         [0011]    The exemplary subunit  10  has a jacket  20  with a wall thickness T 1  in the range of 0.3-0.5 mm, such as about 0.4 mm, and is constructed of plenum PVC which is adequate to pass NFPA-262 testing and to meet ICEA-596 mechanical requirements. A thin riser PVC is used for the insulation  36  of the conductors  30 . Thin wall insulation  36 , with a thickness in the range of 0.007-0.013 mm, facilitates passing burn tests. The exemplary insulation  36  has a thickness of about 0.010 mm. A thicker jacket  20  may be utilized to make the cable  10  more robust and to account for thicker insulation on the conductors  30 . The aramid yarn  50  serves to prevent jacket to conductor tacking and also provides tensile strength. The diameter D 1  of the subunit  10  can be in the range of 4-4.5 mm, the diameter D 2  of the micromodules  40  can be in the range of 1.3-1.7 mm, and the diameter D 3  of the conductors  30  can be in the range of 1.3-1.7 mm. The conductors  30  can be from 18-22 AWG. In the exemplary embodiment, the diameter D 1  is about 4.25 mm, the diameter D 2  is about 1.5 mm, and the diameter D 3  is about 1.5 mm. 
         [0012]      FIG. 2  is a cross-sectional view of a micromodule or “array” cable  100  that includes a plurality of the subunits  10 . The exemplary micromodule cable  100  includes a cable jacket  120  surrounding three subunits  10 , although additional subunits  10  could be incorporated into the micromodule cable  100 . 
         [0013]    According to one application, the micromodule cable  100  can be used to provide power and data to multiple remote antenna units (RAU) in a radio-over-fiber (RoF) system. Other electronic devices could also be connected by the cable  100 . The micromodule cable  100  can be plenum-rated, with the subunits  10  including four optical fibers  42  for transmitting data and two, 20 AWG conductors  30  for transmitting electrical power, and data, if desired. The number of optical fibers can be increased or decreased in the micromodules. Multiple pairs of conductors  30  can be included in each subunit  10  to power additional devices. The jacket  120  of the micromodule cable  100  and the jackets  20  of the subunits  10  can be made from fire-retardant materials, such as, for example, highly-filled PVC. Use of fire-retardant materials can be selected so that the micromodule cable  100  can pass the National Fire Protection Association (NFPA) 262 burn test so as to achieve plenum burn rating. Zero halogen materials can alternatively be used. The exemplary micromodule cable  100  is Class 2 Plenum Cable (CL2P) Rated for low voltage applications, which allows the cable  100  to be installed with less stringent installation procedures. 
         [0014]    Within the subunits  10 , the micromodules  40  can be SZ stranded with the conductors  30 . The subunits  10  can then be helically or SZ stranded within the micromodule cable jacket  120 . A layer of talc may be applied over the subunits  10  to reduce friction when accessing the subunits  10  in the cable  100 . The micromodule cable  100  can be constructed for use in parallel optics systems and having low skew within the subunits  10 . The micromodule cable  100  can have an outside diameter D 4  in the range of 10.5-11.6 mm, and an inside diameter D 5  in the range of 8.7-9.5 mm. The exemplary cable  110  has an outside diameter D 4  of about 11.15 mm and an inside diameter D 5  of about 9.15 mm. 
         [0015]      FIG. 3  is a longitudinal cross-section illustrating a method of accessing individual subunits or “tether” cables  10  in the cable  100 . According to one aspect of the present embodiment, a cut can be made in the jacket  120  at a first location (to the right in  FIG. 3 ) where the desired subunit  10  that needs to be accessed can be severed. The cable jacket  120  can be cut a second location (to the left in  FIG. 3 ) a distance L from the first location, where the subunit  10  can be pulled from the cable jacket  120 . The subunits  10  can be color-coded so that the severed subunit  10  can be easily identified. The severed subunit  10  may then be pulled out a distance approximately equal to the distance L and terminated to a remote antenna unit or some other remote electronic device. The cable  100  is constructed so that at a length L of least 0.7 m, a subunit  10  can be removed when stranded at a 450 mm pitch using a tensile force of ≦20 N. Longer lengths may also be removed with up to 2.0 m being accessed at higher tensile forces. 
         [0016]    The subunits  10  can be broken out of the micromodule cable  100  for connection to external electronics, such as remote antenna units. In this context, the micromodule cable  100  is commonly referred to as an “array” or “tail” cable. The subunits  10  are referred to as “tether” cables. If the distance from the micromodule cable  100  to a remote device such as an RAU is too great, a subunit  10  may be connected to a separate tether cable of longer length that is used to connect to the RAU. The separate tether cable may be of identical construction to the subunits  10 . Tether cables can be used to extend the distance the RAUs are positioned from the array cable  100  by a typical distance of 1-10 m. 
         [0017]    The remaining subunits  10  can be accessed using the same procedure at different longitudinal positions along the micromodule cable  100 . The subunits can each be connected to one or more electronic devices. 
         [0018]    As disclosed, the micromodule cable  100  can satisfy scalable power and optical data connectivity to one or more remote RAUs, using one or more power supply units for DC power. A single cable  100  can connect to multiple RAUs arranged in series, avoiding the need to pull multiple array cables. The cable  100  allows easy access to the micromodules  40  and to the conductors  30 , with each conductor  30  being individually accessible at any access point. A significant length (e.g., 0.7 m or more) of each subunit  10  can be accessed, as shown in  FIG. 3 , to allow significant optical  42  fiber and power conductors  30  for termination—either directly to a remote device, or to a separate tether cable. If the RAU is close enough to the array cable  100 , a subunit  10  accessed from the cable  100  may connect directly to the RAU. 
         [0019]    Bend enhanced optical fibers can be utilized to allow smaller lighter tether and subunit  10  designs to meet ICEA-596 requirements for crush. Examples of suitable optical fibers for use in the cables disclosed in this application include single and multi-mode optical fibers, such as optical fibers available from Corning Incorporated under the trademarks InfiniCor®, SMF-28®, Vascade®, SMF-28e®, ClearCurve®, and LEAF®. 
         [0020]    Although the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.