Abstract:
Armored fiber optic cables and methods for making are disclosed that include an armor layer generally surrounding a fiber optic cable that includes at least one optical waveguide and a cable jacket. The cable jacket has an outer diameter and armor layer has an inner surface, wherein a gap exists between the outer diameter of the cable jacket and the inner surface of the armor layer. The armored fiber optic cable further includes a centering element disposed in the gap between the fiber optic cable and the armor layer. The centering element generally inhibits the fiber optic cable from moving away from a middle of the armored fiber optic cable towards the inner surface of the armor layer during winding of the armored fiber optic cable, thereby inhibiting wavy armor and/or preserving the optical performance of the at least one optical waveguide.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to an armored fiber optic cable and methods for making the same. More particularly, the present invention relates to armored fiber optic cables having a centering element for keeping the cable in the middle of the armor during manufacturing.  
       BACKGROUND OF THE INVENTION  
       [0002]     Communication networks are used to transport a variety of signals such as voice, video, data transmission, and the like. As communication applications required greater bandwidth, communication networks switched to cables having optical fibers since they are capable of transmitting an extremely large amount of bandwidth compared with a copper conductor. Moreover, a fiber optic cable is much lighter and smaller compared with a copper cable having the same bandwidth capacity.  
         [0003]     Consequently, fiber optic cables are used in a wide variety of applications and must meet specific criteria for the given application while preserving optical performance. For instance, fiber optic cables may be used in indoor, outdoor, or indoor/outdoor applications. These different applications have different requirements for satisfying the operating conditions for the fiber optic cable and/or preserving optical performance. By way of example, indoor fiber optic cables require meeting minimum standards for flame and/or smoke propagation since they are intended for use within a building. Similarly, outdoor applications expose fiber optic cables to environmental effects such as temperature variations and/or water. In other applications, fiber optic cables may require a robust covering for protecting the fiber optic cable from open flames and/or mechanical forces such as tensile or crush forces.  
         [0004]     One known way for protecting a fiber optic cable from open flames and/or mechanical forces is by using a rugged armor layer disposed about the fiber optic cable for protecting the same. Generally speaking, an armor layer inhibits open flames from directly reaching the fiber optic cable and may delay the production of smoke from the cable when exposed to open flames if the armor layer is the outside layer. Additionally, the armor layer generally increases the ability of the fiber optic cable to withstand crush and/or tensile forces.  
         [0005]     However, manufacturing fiber optic cables with an armored layer can present certain challenges for preserving optical performance. For instance, one armored fiber optic cable design uses an interlocking armor loosely disposed about the fiber optic cable so the interlocking armor may be easily removed if desired. Because the interlocking armor is loosely disposed about the fiber optic cable the interlocking armor can have a length that is different from the fiber optic cable, thereby causing the formation of wavy armor along the longitudinal length thereof. In order to inhibit the formation of wavy armor during manufacturing, relatively high processing tensions are used. But using relatively high processing tensions can cause other problems during manufacturing. By way of example, the optical fibers of the armored fiber optic cable may have relatively high optical attenuation due to the application of relatively high processing tensions. Usually, after a period of time the optical fibers relax from the application of relatively high processing tensions and the optical attenuation values return to acceptable levels, but some of the cables may need to be temperature cycled in order to relax the optic fibers, thereby relieving the process induced strain. The present invention addresses the problems associated with manufacturing armored fiber optic cables where the armor is loosely disposed about the fiber optic cable.  
       SUMMARY OF THE INVENTION  
       [0006]     One aspect of the present invention is directed to an armored fiber optic cable having a fiber optic cable having at least one optical waveguide and a cable jacket and an armor layer generally surrounds the fiber optic cable with a centering element therebetween. The cable jacket has an outer diameter and armored layer has an inner surface, wherein a gap exists between the outer diameter of the cable jacket and the inner surface of the armor layer. The centering element is disposed in the gap between the fiber optic cable and the armor layer for inhibiting the fiber optic cable from moving away from a middle of the armored fiber optic cable towards the inner surface of the armor layer during winding of the armored fiber optic cable. Consequently, the optical performance of the at least one optical waveguide is preserved by inhibiting the strain placed on the optical fiber(s) during manufacturing.  
         [0007]     Another aspect of the present invention is an armored fiber optic cable having a fiber optic cable, a centering element, and an armor layer. The centering element is disposed in a gap between an outer diameter of the fiber optic cable and an inner surface of the armor layer. The centering element surrounds less than an entire circumference of the fiber optic cable, wherein the centering element generally inhibits the fiber optic cable from moving away from a middle of the armored fiber optic cable towards the inner surface of the armor layer during winding of the armored fiber optic cable, thereby preserving the optical performance of the at least one optical waveguide.  
         [0008]     Yet another aspect of the present invention is directed to an armored fiber optic cable having a fiber optic cable having at least one optical waveguide, at least one strength element and a cable jacket and an interlocking armor layer generally surrounds the fiber optic cable with a centering element therebetween. The cable jacket has an outer diameter and armored layer has an inner surface, wherein a gap exists between the outer diameter of the cable jacket and the inner surface of the armor layer. The centering element is disposed in the gap between the fiber optic cable and the armor layer for inhibiting the fiber optic cable from moving away from a middle of the armored fiber optic cable towards the inner surface of the armor layer during winding of the armored fiber optic cable, thereby preserving the optical performance of the at least one optical waveguide.  
         [0009]     It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principals and operations of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view of a conventional armored fiber optic cable.  
         [0011]      FIG. 2  is a partial cut-away schematic representation of the conventional armored fiber optic cable of  FIG. 1  being bent over a capstan during the manufacturing process.  
         [0012]      FIG. 3  is a cross-sectional view of the conventional fiber optic cable on the capstan of  FIG. 2  taken along the line  3 - 3 .  
         [0013]      FIG. 4  is a cross-sectional view of an armored fiber optic cable according to the present invention.  
         [0014]      FIG. 5  is a cross-sectional view of the armor fiber optic cable of  FIG. 4  disposed a capstan during the manufacturing process.  
         [0015]      FIG. 6  is a cross-sectional view of the centering element of the fiber optic cable of  FIG. 4 .  
         [0016]      FIG. 7  is a cross-sectional view of another armored fiber optic cable according to the present invention.  
         [0017]      FIG. 8  is a flowchart showing exemplary steps for manufacturing a fiber optic cable according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.  FIG. 1  depicts a perspective view of a conventional armored fiber optic cable  10  (hereinafter armored cable  10 ) having a fiber optic cable  17  and an interlocking armor layer  18  therearound for providing additional protection to fiber optic cable  17 . Fiber optic cable  17  includes a central strength member  11  having a plurality of optical waveguides such as optical fibers  12  having a buffer layer (not numbered) stranded therearound, a plurality of strength elements  13 , and a cable jacket  16 . As shown, a gap G exists between an outer diameter (not numbered) of the cable jacket  16  and an inner surface  18   a  of the interlocking armor layer  18 . Using gap G between fiber optic cable  17  and interlocking armor layer  18  eases the removal of relatively long lengths of interlocking armor layer from fiber optic cable  17 . In other words, the armor layer  17  is not bound to a portion of fiber optic cable  17  so it can easily be removed if desired. However, gap G also allows fiber optic cable  17  to move radially within the interlocking armor layer  18  such as during manufacturing.  
         [0019]     More specifically,  FIG. 2  depicts a partial cut-away schematic representation of conventional armored fiber optic cable  10  being bent over, for instance, an exemplary capstan  22  during the manufacturing process. Moreover, similar effects occur using other cable manufacturing equipment that places the fiber optic cable in a bend such as caterpuller, reel, or the like. As shown, gap G allows fiber optic cable  17  to move toward the inside surface  18   a  of interlocking armor layer  18  when relatively high tensions are applied so that the bending radii of the fiber optic cable  17  and interlocking armor layer  18  are different. Stated another way, a bending radius of the interlocking armor layer r a  is greater than a bending radius of the fiber optic cable r c . This difference in bending radii is also depicted in  FIG. 3 , which shows a cross-sectional view taken along line  3 - 3  of the conventional armored fiber optic cable  10  on capstan  22 . Consequently, the different bending radii between interlocking armor layer  18  and fiber optic cable  17  can cause a length difference between the interlocking armor layer and fiber optic cable  17  (i.e., the length of fiber optic cable  17  is shorter than interlocking armor layer  18 ), thereby allowing the formation of wavy armor when the armor fiber optic cable is unspooled from the reel. Stated another way, since fiber optic cable  17  and interlocking armor layer  18  are not coupled together fiber optic cable  17  they can travel at different speeds to cause wavy armor.  
         [0020]     The present invention solves the problems of wavy armor and/or optical attenuation issues caused by loosely forming the armor layer about the fiber optic cable with a gap therebetween. More specifically, the present invention uses a centering element disposed between the fiber optic cable and the armor layer for inhibiting fiber optic cable from moving away from the middle of the armor layer disposed therearound. In other words, the centering element inhibits the fiber optic cable from moving away from the middle of the armor layer while still allowing a gap between the armor layer and the fiber optic cable so that the armor layer can be easily removed.  
         [0021]      FIG. 4  is a cross-sectional view of an armored fiber optic cable  40  according to the present invention. As shown, armored fiber optic cable  40  includes fiber optic cable  17 , a centering element  45 , and an armor layer  18 . Centering element  45  is disposed between fiber optic cable  17  and armor layer  18  for inhibiting fiber optic cable  17  from moving toward an inner surface  18   a  of armor layer  18 . Centering element may also have different orientations within the armor layer such as being relatively straight or helically wrapped about fiber optic cable  40  with a suitable pitch. By way of example,  FIG. 5  depicts a cross-sectional view of armor fiber optic cable  40  disposed on capstan  22  such as during manufacturing of the same. As depicted, the bending radii of armor layer  18  and fiber optic cable  17  are the same or nearly equal so that they travel at the same speed about the capstan. Consequently, the formation of wavy armor and/or optical attenuation issues are advantageously inhibited since fiber optic cable  17  is inhibited from moving towards inner surface  18   a  of armor layer  18 .  
         [0022]      FIG. 6  is a cross-sectional view of centering element  45  of armored fiber optic cable  40 . Centering element  45  may be formed from any suitable material such as a polymer, metal, paper, or the like formed into a longitudinal tape. For instance, suitable polymers include polyethylene, polypropylene, polyvinylchloride, PVDF, mylar, blends thereof, or the like. In other embodiments, centering element  45  may be formed from a metal tape such as steel, aluminum, etc. Centering element  45  is shown laid out flat and has a width W and a height H. Height H is selected so that fiber optic cable is maintained at or near the center of armor layer  48 . Illustratively, if gap G is about 5 millimeters, then height H of centering element is selected so that it is about 5 millimeters. In one embodiment, width W of centering element  45  is selected so that it surrounds less than an entire circumference of fiber optic cable  17  such as about 1/10 of the circumference of the fiber optic cable to reduce the amount of material used, thereby reducing expense. However, any suitable width of centering element is possible using the concepts of the present invention.  
         [0023]     In one embodiment, fiber optic cable  17  is flame-retardant so it is suitable for indoor use such as plenum, riser, and/or LSZH (low smoke zero halogen) applications. Fiber optic cable  17  is made flame-retardant by, for example, using suitable combinations of polymers for the buffer layer disposed about each individual optical fiber and/or the cable jacket. By way of example, the buffer layer about the individual optical fiber is PVC and the cable jacket is also formed of a PVC; however, other suitable materials may be used to create a flame-retardant cable. Likewise, the centering element may also be formed of a flame-retardant material such as a PVC or the like.  
         [0024]     As depicted, armored fiber optic cable  40  uses an interlocking armor for armored layer  18 , but any suitable armor layer may be used. The interlocking armor layer is spirally wrapped about fiber optic cable  17  and successive wraps of the armor attach to the previous wrap, thereby making a relatively flexible armor layer, while inhibiting over-bending of the same since the interlocking armor has a minimum bending radius. Suitable metal tapes for forming interlocking armor is available from Alcan of Canada.  
         [0025]      FIG. 7  is a cross-sectional view of armored fiber optic cable  70  according to another embodiment of the present invention. Armored fiber optic cable  70  includes a fiber optic cable  71 , a centering element  75 , an armor layer  78 , and a second jacket  79  disposed radially outward of armor layer  18 . In this embodiment, cable  71  includes a plurality of optical fibers  12  that exclude a buffer layer therearound. In other words, optical fibers  12  are the coatings thereof to contact each other. The plurality of optical fibers  12  are arranged in a bundle and secured with a binder (not visible) such as a thread, paper tape, or the like. A plurality of strength members  73  such as aramid or fiberglass are stranded about the bundle for providing tensile strength to fiber optic cable  71  so that some of the optical fibers  12  may contact some of the strength members  73 . A cable jacket  74  is disposed about the plurality of strength members  73  for providing protection for fiber optic cable  71 .  
         [0026]     In this embodiment, the width W of centering element  75  is selected to so that contacts a larger arc of the fiber optic cable than the embodiment shown in  FIG. 4 . In other words, the width W of centering element  75  is selected to contact slightly less than have of the periphery of fiber optic cable  71 . Additionally, armored fiber optic cable  70  includes a second jacket disposed radially outward of armor layer  18 . Likewise, other embodiments of the present invention may include a second jacket radially outward of the armor layer.  
         [0027]     Exemplary steps for making a fiber optic cable according to the present invention are shown in  FIG. 8 . Manufacturing process  80  includes a step  82  of paying off a fiber optic cable, a step  84  of placing a centering element adjacent to the fiber optic cable, and a step  86  of forming an armor layer about the fiber optic cable and the centering element. Optional steps may include a step  88  of forming a cable jacket radially outward of the armor layer or a step of having a larger tension on the centering element than the cable when paying off. Keeping a higher tension on the centering element maintains the position of the centering element against the armor during manufacturing.  
         [0028]     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention. For instance, the concepts described herein can be applied to any suitable fiber optic cable designs. Likewise, fiber optic cables may include other suitable cable components such as ripcords. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.