Abstract:
This invention is a method and system for addressing structural weaknesses and geometric differentials introduced to a cable when splicing optic fibers. The apparatus and method utilize structurally integrated layers of protective polymers and bonding materials selected for strength and flexibility relative to their thickness. This results in an apparatus having a minimally increased circumference compared to the cable. The method and apparatus include one or more strengthening layers which allow the repaired cable substantially similar flexibility compared to the cable, but prevent formation of sharp bends or kinks. The strengthening layers also allow the repaired cable a resistance to tension similar to the original cable. The method and apparatus further include an outer layer having a geometric configuration which includes sloped terminating ends designed to prevent the reinforced area of the cable from being damaged by the force of objects or substances in contact with cable.

Description:
FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
       [0001]    This invention is assigned to the United States Government. Licensing inquiries may be directed to Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif., 92152; telephone (619) 553-5118; email: ssc_pac_t2@navy.mil. Reference Navy Case No. 102146. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    This invention relates to the field of optical waveguide repair, and more specifically, to a multi-layered apparatus and system for addressing structural differentials introduced when optical cables are spliced. 
         [0004]    2. Background 
         [0005]    Optical fiber cables, known for their high speed and bandwidth, are brittle glass or polymer fibers surrounded by a protective layer. Fiber optic cables can include large numbers of signal-carrying fibers, each fiber having a diameter of less than a human hair. The fiber-optic “bundle” is protected by an outer cable casing. 
         [0006]    Fiber optic cables are often buried or submersed, and effectively under high pressure below ground or under water. They may need to be removed and redeployed which can include being rewound on reels. They may also be subjected to pulling forces (“tension”) when the cable is being deployed. 
         [0007]    The thin filament fibers within a cable may break when the outer housing of a cable is pierced, bent sharply (“kinked”) or crushed. When a breakage in the fibers occurs, each fiber must be spliced back together. Two fiber segments are positioned end-to-end and heat fused to form a single optical fiber. 
         [0008]    It is well known in the art that once the cable is repaired, the repaired cable is at a high risk of subsequent breakage due to several specific factors known in the art that contribute to this risk. 
         [0009]    First, there is increased vulnerability because the original protective layers of the cable must be stripped during the repair process. It is a problem known the art that after a repair, when the structural layers are not restored, the cable is substantially weakened and does not have the same resistance to tension, bending or the original conditions which caused the cable to break prior to the repair. 
         [0010]    Second, the splicing operation and/or makeshift strengthening and protecting measures result in geometric abnormalities and protuberances on the outer surface of cable which may cause the repaired cable to catch or snag objects moving across its surface. This may cause damage to the cable when moving or respooling. 
         [0011]    Third, many repair processes result in rigid cable segments which are vulnerable to breakage because they cannot curve gently. This subjects the cable to kinking at a sharp angle at each end of the rigid segment. 
         [0012]    Many attempts have been made in the prior art to reinforce fiber optic cable after a repair operation has been completed. For example, U.S. Pat. No. 5,884,003 A to Randy G. Cloud et al. (Cloud &#39;003) teaches the use of a rigid case for enclosing and storing optical cable splices. While the Cloud &#39;003 device may protect the splice, it creates problems associated with the storage and transportation of fiber optic cable. Use of this prior art device, and others like it, results in large, rigid segments of cable that cannot be easily wound on a spooling device for storage. Furthermore, the cable is vulnerable to kinking at each end of the rigid case. 
         [0013]    Current repair methods and kits do not restore the structure of the original layers, focusing instead on providing a portable sleeve that can be used to rapidly cover the splice. The shrink-wrapped covering provides a simple mechanical interface but does not provide multiple layers of protection. Commercially available kits often comprise a single type of fusion splice sleeve for use after a fusion splicing operation. These kits may be a good on-site solution, but alone it has been shown in the art that they are inadequate to assure continued, reliable communications after a repair. 
         [0014]    It is desirable to have a multi-layered splice protection apparatus or system which retains near to the original diameter of the cable, avoids creating a rigid segment, approaches the stiffness of the original cable, and continues to hold the same tension as the original cable in service. 
       SUMMARY OF THE INVENTION 
       [0015]    This invention is a method and system for addressing structural weaknesses and geometric differentials introduced to a cable when splicing optic fibers. The apparatus and method for fiber optic cable repair utilize structurally integrated layers of protective polymers and bonding materials selected for strength and flexibility relative to their thickness. This results in an apparatus having a circumference that is minimally increased over that of the fiber optic cable. The method and apparatus include one or more polymer strengthening layers which allow the repaired cable sufficient flexibility, but prevent formation of sharp bends which are characteristic of spliced areas. The method and apparatus further include an outer layer having a geometric configuration which includes sloped terminating ends designed to prevent the reinforced area of the fiber optic cable from being damaged by the force of objects or substances in contact with cable. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIGS. 1   a  and  1   b  illustrate a side view and a cross-sectional view, respectively, of an exemplary layered optical fiber splice protection system. 
           [0017]      FIGS. 2   a  through  2   e  separately illustrate the structural properties of each layer of an exemplary layered optical fiber splice protection system. 
           [0018]      FIG. 3  illustrates an exemplary method for applying a layered optical fiber splice protection system. 
       
    
    
     TERMS OF ART 
       [0019]    As used herein, the term “bending modulus E” means a value of the tendency for a material to bend. Bending modulus is measured as force per unit area. 
         [0020]    As used herein, the term “plurality” means a quantity of two or more. 
         [0021]    As used herein, the term “tension modulus K” means a value of the maximum pulling force that a material can withstand before breaking. Tension modulus is measured as force per unit area. 
         [0022]    As used herein, the term “substantially” means all or partially in a manner to effect function, operation or results. 
       DETAILED DESCRIPTION OF INVENTION 
       [0023]      FIGS. 1   a  and  1   b  illustrate a side view and a cross-sectional view, respectively, of an exemplary layered optical fiber splice protection system. 
         [0024]    The exemplary layered optical fiber splice protection system  100  of  FIGS. 1   a  and  1   b  has an optical cable  10 , an optical fiber  15  having an outer surface  17 , a splice contact tube  20  with an inner surface  22  and an outer surface  24 , a retaining tube  30  with a retaining tube inner surface  32 , a retaining tube outer surface  34 , and an adhesive moisture barrier layer  35 , strengthening tube  40  with an internal tube surface  42 , an optional longitudinal slit  43 , an external tube surface  44 , a tube adhesive layer  45 , at least one structural reinforcement component  47  and first and second terminating outer rims  49   a  and  49   b , an optional curable layer  50 , an outer sleeve  60  with an internal sleeve surface  62 , a tubular center section  64 , a sleeve adhesive layer  65  and first and second sloped terminating ends  69   a  and  69   b , and at least two optional securing components  70   a  and  70   b  each having an inner pressure surface  72   a  and  72   b , respectively. 
         [0025]      FIGS. 2   a  through  2   c  illustrate the structural alteration which occurs during each step of the prior art repair process.  FIG. 2   a  shows the optical cable  10  having an external cable diameter CD. Optical cable  10  is made up of an optical fiber  15  typically surrounded by protective components such as cladding, a coating, a buffer, armored cladding, an aramid synthetic fiber sheath, or a cable jacket. During splicing, all of these protective components are stripped back from optical fiber  15  to permit performance of a splicing connection operation on optical fiber  15 .  FIG. 2   b  illustrates the structural properties of an exemplary first layer of an optical fiber splicing system. A reinforced splice contact tube  20  placed over the optical fiber  15  structurally conforms to the outer surface  17  of optical fiber  15 .  FIG. 2   c  illustrates the structural properties of an exemplary second layer of an optical fiber splicing system. Retaining tube  30  is located over the splice contact tube  20  and structurally conformed to the splice contact tube  20 . An adhesive moisture barrier layer  35  disposed on the retaining tube inner surface  32  bonds with the outer surface  24  of splice contact tube  20  to prevent moisture intrusion ( FIG. 1   b ). In various embodiments, splice contact tube  20  and retaining tube  30  may lack reinforcement or adhesive layers or have a reduced wall thickness. These alternate embodiments reduce the overall profile of the layered optical fiber splice protection system  100 . 
         [0026]      FIG. 2   d  illustrates the structural properties of an exemplary third protective layer of an optical fiber splice protection system. Strengthening tube  40  is located over retaining tube  30 . Tube adhesive layer  45  ( FIG. 1   b ) seals it to optical cable  10 . Optional curable layer  50 , injectable through the longitudinal slit  43  ( FIG. 1   b ) into the volume between internal tube surface  42  and retaining tube  30 , prevents kinking or splitting of the strengthening tube  40 . Optionally, at least two securing components  70   a  and  70   b  clamp around strengthening tube  40 . 
         [0027]    Strengthening tube  40  is has an internal tube diameter TD 1  and an external tube diameter TD 2 . Optionally, strengthening tube  40  has an embedded structural reinforcement component  47  ( FIG. 1   b ). Strengthening tube  40  may also have a longitudinal slit  43  ( FIG. 1   b ) for ease of application. The tube adhesive layer  45  on an internal tube surface  42  will adhere strengthening tube  40  to optical cable  10  and prevent strengthening tube  40  from splitting or slipping. Strengthening tube  40  is can be made from materials including, but not limited to polymers, natural or synthetic fiber braid, natural or synthetic rubber tubing, or other solid materials such as flexible metal tube, metal braid, or springs. Strengthening tube  40  may be a clear polymer to permit proper positioning of strengthening tube  40  and visualization of curable layer  50 . 
         [0028]    The internal tube diameter TD 1  of the strengthening tube  40  is greater than the external cable diameter CD of optical cable  10  to enable strengthening tube  40  to be applied around optical cable  10 . The strength modulus K s  of strengthening tube  40  is equal to or greater than the strength modulus K o  of optical cable  10  along the axis of the cable. Thus, two or more of the optional securing components  70   a  and  70   b  will be required if the adhesive shear strength of the sleeve adhesive layer  45  is insufficient to carry the tension of optical cable  10 . The bending modulus E s  of strengthening tube  40  when added to the optical cable  10  is within about ten percent above or below the bending modulus E o  of optical cable  10 . This prevents excessive bending from being exerted on the optical fiber  15  and prevents optical cable  10  from kinking over first and second terminating outer rims  49   a  and  49   b.    
         [0029]    The structural reinforcement component  47  is an optional component which increases the tension modulus K s  of strengthening tube  40 . In embodiments where the tension modulus K s  of strengthening tube  40  alone would not be a sufficient match to the tension modulus K o  of optical cable  10 , structural reinforcement component  47  can be utilized by strengthening tube  40 . The structural reinforcement component  47  may be shaped as, but not limited to, at least one band, braid, helix, mesh, sheet or strip. The structural reinforcement component  47  ( FIG. 1   b ) may be fabricated from materials such as, but not limited to, aramid, carbon, metallic and nylon materials. 
         [0030]    Optional curable layer  50  may be, but is not limited to, a silicone, epoxy, silicone composite or epoxy composite material. Curable layer  50  is generally a fluid, injectable material which cures in situ to a solid to prevent kinking or splitting the strengthening tube  40 . 
         [0031]    The at least two optional securing components  70   a  and  70   b  may be, but are not limited to, a first ring-shaped pressure component  70   a  and a second ring-shaped pressure component  70   b . These securing components  70   a  and  70   b  may be added in pairs placed a first distance D 1  and a second distance D 2 , respectively, from the first and second terminating outer rims  49   a  and  49   b . Respective inner pressure surfaces  72   a  and  72   b  ( FIG. 1   a ) provide pressure on the strengthening tube  40  when applied. 
         [0032]      FIG. 2   e  illustrates the structural properties of an exemplary fourth layer of an optical fiber splice protection system. The outer sleeve  60  is located over strengthening tube  40  and sealed to strengthening tube  40  and optical cable  10 . The sleeve adhesive layer  65  on internal sleeve surface  62  prevents outer sleeve  60  from slipping from position. Outer sleeve  60  has a strength modulus K c  and a bending modulus E c . 
         [0033]    Outer sleeve  60  is fabricated from a heat-shrinkable material, a mechanically expanded polymer material which shrinks in one plane when heated. A tube of heat-shrinkable material shrinks in diameter when heated and activates sleeve adhesive layer  65  upon heating. Heat-shrinking outer sleeve  60  results in a tubular center section  64  having a first internal sleeve diameter SD 1  approximately equal to external tube diameter TD 2 . Furthermore, first and second sloped terminating ends  69   a  and  69   b  have maximum internal diameters MD 1  approximately equal to internal diameter SD 1  which gradually slope down to minimum internal diameters MD 2  approximately equal to external cable diameter CD. This provides a smoother, more continuous surface over first and second terminating outer rims  49   a  and  49   b  of strengthening tube  40 , preventing them from catching and causing damage to strengthening tube  40 . 
         [0034]    Outer sleeve  60  once installed may have an external sleeve diameter SD 2  in the range of about 10% to about 100% of the external cable diameter CD of optical cable  10 . External sleeve diameter SD 2  must be minimized to prevent the outer diameter of system  100  from significantly exceeding the outer diameter of optical cable  10 . Outer sleeve  60  substantially encloses strengthening tube  40 . 
         [0035]    In another exemplary embodiment of optical fiber splice protection system  100 , the outer sleeve  60  is provided as a single unit layered with the strengthening tube  40 . In this exemplary embodiment, both strengthening tube  40  and outer sleeve  60  are applied to optical cable  10  simultaneously. Heat-shrinking outer sleeve  60  simultaneously applies pressure to seal the tube adhesive layer  45  to optical cable  10 . 
         [0036]    In an alternate embodiment, outer sleeve  60  may be added directly over the optional curable layer  50  if its tension modulus K c  and bending modulus E c  are a sufficient match to the tension modulus K o  and bending modulus E o  of optical cable  10 . 
         [0037]      FIG. 3  illustrates an exemplary method for applying a layered optical fiber splice protection system. 
         [0038]    In Step  301 , a user strips back protective components of optical cable  10  to expose the severed optical fiber  15  and positions the splice contact tube  20 , retaining tube  30 , strengthening tube  40  and outer sleeve  60  on optical cable  10 . At Step  302 , the user performs a splicing connection operation on optical fiber  15 . At Step  303 , the user positions the splice contact tube  20  over the now-spliced optical fiber  15  and shrinks splice contact tube  20  using applied heat. At Step  304 , the user positions the retaining tube  30  over splice contact tube  20  and shrinks retaining tube  30  using applied heat. At Step  305 , the user moves strengthening tube  40  over retaining tube  30 . At Step  306 , the user applies pressure to strengthening tube  40  to seal tube adhesive layer  45  to optical cable  10 . At optional Step  307 , the user injects curable layer  50  through the longitudinal slit  43  of strengthening tube  40  into a volume between internal tube surface  42  and retaining tube  30 . At optional Step  308 , the user clamps strengthening tube  40  to optical cable  10  with at least two securing components  70   a  and  70   b . Finally, at Step  309 , the user positions the outer sleeve  60  over strengthening tube  40  and shrinks outer sleeve  60  using applied heat. 
         [0039]    It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated to explain the nature of the invention, may be made by those skilled in the art within the principal and scope of the invention as expressed in the appended claims.