Abstract:
A fiber optic cable has at least two round strength members, at least one fiber optic element, with the strength members and the fiber optic element forms a core. A jacket surrounds the core elements. The strength members are arranged side by side within the jacket such that the inside diameter of the jacket is substantially equal to the combined diameters of the two round strength members and where within the jacket there are two voids not filled by the round strength members. The at least one fiber optic element is positioned in one of the voids the round strength members is dimensioned such that when the fiber optic element is within the void, it does not reach the inside surface of the jacket.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This application relates to cables. More particularly, this application relates to a fiber optic aerial drop cable. 
         [0003]    2. Related Art 
         [0004]    In the area of aerial drop cables, when a cable is to be dropped after splicing from a larger line to a terminus point, such as a house or business building, the aerial drop cables typically have both a signal component and a strength component. The strength component bears the weight of the line tension to the terminus point. 
         [0005]    Typically aerial drop cables, as shown in  FIG. 1 , have a flat arrangement, with two GRPs (Glass Reinforced Polymers) on either side of the fiber element, enclosed within a jacket. When such a cable is connected, a wedge clamp is used. These wedge clamps, although effective tend to be of a slighter design and occasionally exhibit mechanical failure. 
         [0006]    Aside from the flat drop aerial cables of  FIG. 1 , using a special wedge clamp, the flat design is atypical relative to other (round) cables and thus requires special handling. For instance, owing to the flat design, it is difficult to bend in various directions, particularly in the plane of the strength members. This makes the cable design difficult to install. An ordinary round cable has a preferred geometry for bending and other mechanical considerations (overall robustness of design) but they can not be used in a wedge clamp. 
         [0007]    Separately, a different form of connection joint may be employed for round type aerial drop cable designs (power, signal, etc . . . ) using a dead end connection, particularly a helical type dead end pictured in prior art  FIG. 2 . A dead end connector typically uses helically wrapped metal wires W that clamp to the end of the cable C and form a loop L to connect to a terminus point. 
         [0008]    To attach the clamp to a wire/cable, various strands of pre-wound spiral wires from the end of the dead end are each wrapped around the outer jacket of the cable to be clamped until there is an overall tight fit on the cable. The friction and grip force against the jacket hold the cable within the connector. 
         [0009]    However, these pre-wound spiral wires tend to compress against the round outer jacket of the cable until the components within the jacket resist the compression force. Such a connection type can not be used on flat cable designs. And, although such connection styles may be used on round power/copper cables they can not be used on existing round fiber optic cables as the compression force necessary to clamp the dead end to the jacket causes too much compression on the fibers within, resulting in increased chances for attenuation or other such damage to those fibers. 
       OBJECTS AND SUMMARY 
       [0010]    The present application addresses the issues of the prior art and provides a round style fiber cable, for use in aerial drop applications, that is arranged so that the fiber component is not crushed during a dead end type termination. Such an arrangement allows for the use of preferred round style cables in an aerial drop situation, utilizing a typical round cable connector such as a dead end. 
         [0011]    To this end, a fiber optic cable is provided with at least two round members, such as strength members, metallic wires, or insulated copper conductors and at least one fiber optic element, where the strength members and the fiber optic element form a core. A jacket surrounds the core elements. The strength members, metallic wires or insulated copper conductors are arranged side by side within the jacket such that the inside diameter of the jacket is substantially equal to the combined diameters of the two round strength members. Within the jacket there are two voids, not filled by the round strength members. The at least one fiber optic element is positioned in one of the voids. The round strength members are dimensioned such that when the fiber optic element is within the void, it does not reach the inside surface of the jacket. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention can be best understood through the following description and accompanying drawings, wherein: 
           [0013]      FIG. 1  is a prior art illustration of an aerial drop fiber optic cable; 
           [0014]      FIG. 2  is a prior art illustration of an aerial drop dead-end type connection; 
           [0015]      FIG. 3  illustrates the internal components of an aerial drop fiber optic cable, in accordance with one embodiment; 
           [0016]      FIG. 4  illustrates a circle schematic of the core components of the cable, in accordance with one embodiment; 
           [0017]      FIG. 5  illustrates an aerial drop fiber optic cable with a jacket, in accordance with one embodiment; and 
           [0018]      FIGS. 6 and 7  illustrate the aerial drop fiber optic cable of  FIG. 4  inside of the helical wrap of a dead-end type connection, in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    In one arrangement, as shown in  FIG. 3 , three components are combined to form a core  10  of an aerial drop cable  2 . Two GRP (Glass Reinforced Polymers)  12  are arranged in a side by side manner. Both above and below GRPs  12 , tight buffer type optical fiber elements  14  are arranged. 
         [0020]    It is noted that fiber elements  14  are described herein as tight buffer optical fibers (typically 900 micro outer diameter) however this is for illustration purposes through this specification. In another embodiment, fiber elements  14  may be replaced with loose tube fiber element arrangements with a substantially similarly diametered buffer tube with fibers arranged loosely therein. Additionally, fiber elements may be bare 250 micron coated UV fibers without a loose buffer tube if the environmental conditions for the use of cable  2  support such an arrangement. 
         [0021]    Separately, for the purposes of illustrating the salient features of the present invention, the two large elements within core  12  are described as GRPs  12 . However, GRPs  12  may be substituted with either bare metallic wires or insulated conductors or a combination of the two depending on the needs of the particular implementation of cable  2 . Such bare metallic wires or insulated conductors, would, within the scope of the description below, be dimensioned with substantially similar dimensions to the GRPs  12  discussed in detail below. 
         [0022]    It is noted that when any two round elements are wound together to form a larger hypothetical outer circumference, they generate a bundle diameter (circumference) with 2 voids. If a third hypothetical circle were to be placed in either one of those two voids so that it touches the outer circumference of both round elements as well as the inner circumference of the larger hypothetical circle, that third circle would have a circumference of about ⅔ the diameter of either one of the two round elements. This is illustrated schematically in  FIG. 4 . The elements (circular) of GRPS  12  and fiber elements  14  are arranged in such a manner in core  10  of cable  2 . 
         [0023]    However, according to one embodiment as shown in  FIGS. 3  and  FIG. 5  (circle diagram), GRP  12  elements are sized at approximately 2.1 mm diameter. According to the notes indicated above, such diameters, when stranded in core  10 , creates two voids (one above and one below), where each void would create enough space to contain another circle of a diameter of about 1.4 mm (2.1mm×0.67). 
         [0024]    However, as noted above, the elements to be placed in these voids are the tight buffer fiber optic elements  14 , which are only 0.9 mm. 
         [0025]    As a result, when the 0.9 mm optic elements  14  are placed within the voids created by GRPs  12 , they only fill about 67% of the available space in this void or in other words are about 33% smaller than they could be before they would contact the hypothetical circle formed by two twisted 2.1 mm GRPs  12 . 
         [0000]      2.1 mm×0.67=1.4
 
         [0000]      1.4/0.9 mm=1.5 
         [0000]      1.5 (1/ x )=0.67 
         [0000]    or thus the 0.9 mm tight buffers are 33-34% smaller than the hypothetically available 1.4 mm. 
         [0026]    Thus, as shown in  FIGS. 3 and 5 , the oversized GRPs  12  create a buffer of approximately 33-34% to protect tight buffer fiber elements  14  during compression of cable  2 . 
         [0027]    Also, as shown in  FIG. 3 , in addition to GRPs  12  and tight buffer fiber elements  14 , core  10  may also include additional water swellable yarns, water swellable powder (with or without yarns) or strength yarns  16 . For example, in the arrangement shown in  FIG. 3 , each of the tight buffer fiber optic elements  12  has three compressible (cushioned) water swellable yarns  16 . Compressible yarns  16 , like GRPs  14 , allow additional space for the diameter of cable  2 , under clamping stress, to restrict and tighten down with the pressure being better transferred to GRPs  12  but not to tight buffer fiber optic elements  14 . 
         [0028]    In one arrangement, yarns are typically 0.15-0.25 mm thick by about 2-2.5 mm wide. It is noted that the yarns are fibrous and thus these dimensions are approximate as the fibers making the yarn may shift/bunch during application. Under the compression of a dead end clamp, yarns  16  may additionally compress to a thickness of 0.10 to 0.15 mm thickness. 
         [0029]    It is understood that the sizing of individual yarns  16  may result in more or less than three yarns  16  being used for each fiber optic element  14 . Likewise, yarns  16  of different size or compressibility may also be used. 
         [0030]    When yarns  16  are placed on top of fiber elements  14  or within the intercies between GRPs  12  and tight buffer fibers  14 , they do not significantly decrease the buffer space between the fibers  14 /yarns  16  and the inner diameter of the jacket. 
         [0031]    For example, 1.407 (hypothetical allowed diameter before touching the inside surface of the jacket/1.05 mm (size of 0.9 mm fiber with 0.15 mm yarn)=about 30-35% additional spacing. 
         [0032]    In one arrangement, the elements of core  10 , assembled as outlined above, are helically stranded or stranded in an SZ manner in order to provide better flexibility to cable  2 . It is understood that the elements of core  10  may be un-stranded if desired, but for the purposes of illustration, the elements of core  10  are helically stranded. 
         [0033]    As shown in  FIG. 5 , once the elements of core  10  are prepared (arranged and stranded) a jacket  20  is extruded thereover forming the completed aerial drop cable design. Jacket  20  may be formed of any desired polymer, such as Polyethylene, PVC or other common jacketing materials. 
         [0034]    The outer jacket in one arrangement is about 1.27 mm thick resulting in an OD (Outside diameter of about) 6.74 mm (jacket plus two GRPs  12 ). 
         [0035]    Turning to  FIGS. 6  (cross section) and  7  (perspective view), cable  2  is shown within a dead end type clamp, such as that shown in the prior art  FIG. 1 . In  FIG. 5 , the various helically wrapped strands of the metal clamp C are shown constricting downward (centrifugally) onto the outer surface of jacket  20 , compressing the components of core  10 . As shown in  FIG. 6 , this compression occurs over the entire distance of cable  10  within the dead-end type clamp C. 
         [0036]    In one example, the dead end clamp has a pre-spun inner diameter of about 5.5-6 mm. Such a dead end is applied in approximately a quantity of four three-component units at a time by hand wrapping them onto jacket  20  of cable  10 . As pre-spun strands go to their pre-spun inner diameter around jacket  20 , it causes a compression friction fit. The compression is stopped by the resistance of GRPs  12  and jacket  20 . 
         [0037]    The resultant increased diameter of GRPs  12  and the consequent oversizing of the voids by about 30-34% over tight buffer fiber optic elements  14  prevents the helical wrap of dead-end from crushing the fiber element. For example as shown in  FIGS. 6 and 7 , the inner diameter of compressed jacket  20  still does not directly press against the outsides of fiber elements  14 . The dimensions described above are based on the standard size for dead end connectors. Alternative dimensions for the elements of core  10  and jacket  20  may be used for different sized dead ends. 
         [0038]    In one arrangement, it is noted that the various components, particularly yarns  16  and GRPs  12  are helically stranded. Ideally, when the metallic ends of the dead end are wrapped onto jacket  20  the coils should be in an opposite helical lay to the underlying core  10  elements in order to better provide for crush resistance. In any event, the lay is different to such an extent that the GRPs cross the dead end wires in such a way as to provide the anti-compressive structural support. 
         [0039]    While only certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes or equivalents will now occur to those skilled in the art. It is therefore, to be understood that this application is intended to cover all such modifications and changes that fall within the true spirit of the invention.