Abstract:
An armored cable termination/fiber-optic seal which connects a fiber optic cable—the fiber optic cable including one or more armor wires and one or more cable tubes—to a pressure housing, the armored cable termination/fiber-optic seal including: an armored termination which locks the one or more armor wires in a conical cavity; sealing paths which block water from traveling in the interstitial space between the one or more armor wires and the one or more cable tubes into the pressure housing; and fiber feed-through tubes which block water from traveling in the interior of the one or more cable tubes into the pressure housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/539,081, filed on Sep. 26, 2011, in the United States Patent and Trademark Office, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    This application relates to termination of a subsea fiber optic cable, specifically a small form-factor armored cable termination/fiber-optic seal which facilitates a connection between a subsea fiber optic cable and a pressure housing in an environment with a pressure gradient between the external environment and the pressure housing interior. 
         [0004]    2. Description of Related Art 
         [0005]    One of the key challenges in subsea system design is to provide a high-reliability, redundant penetration into 1-atmosphere pressure housings. This task is more difficult in subsea optical systems where a fiber optic cable must be cut to allow for interconnection within a pressure housing. The termination going into this housing should ideally seal the cable tubes and fibers to prevent leakage into the pressure housing, while maintaining the original cable break-strength. 
         [0006]    Several related art methods exist for cable termination and tube and fiber seals, each of which have their own disadvantages. 
         [0007]    Wedge cones, cable compression fittings, and epoxy cones may all be used to terminate various cable types. A wedge cone may be used to terminate armored cable. While wedge cones have sufficiently high strength, wedge cones and housings are specific to their cable type and are labor intensive to terminate. A cable compression fitting which grips cable may be installed with relative ease, but provides relatively lower strength. Epoxy cones—cable tubes and armor wires glued in a cone—can be applied to many cable geometries, but the epoxy used degrades over time and effectiveness is dependent on manufacturing process repeatability. 
         [0008]    Methods for tube and fiber seals include Morrison seals, boot seals, epoxy glands, and ferrule based penetrators. Morrison seals provide bi-directional tube sealing while boot seals are limited to single direction sealing. Because Morrison seals and boot seals only block leakage around a cable tube, they are ineffective in the event of a cable tube breach and leakage with in the cable tube. Epoxy glands—wherein an epoxy seals a fiber tube to form a water tight barrier—may be applied to many cable geometries and provide seals for both tubes and fibers. The fibers and tubes are not individually isolated, however, and may allow pressurized water to leak from tube to tube. Ferrule-based penetrators—where ferrule is soldered onto fiber—provides hermetic seal, but are expensive to deploy and requires additional splices in optical system. 
         [0009]      FIG. 4  illustrates one example of a fiber optic cable  11 . Referring to  FIG. 4 , cable  11  may include a stainless steel central tube  54  containing one or more optical fibers  55  and one or more armor wires  52  wrapped around the central tube  54 . Additional stainless steel cable tubes  53  containing one or more optical fibers  55  may be interspersed in the cable armor wire layers. Cable  11  is jacketed with a cable sheath  51  (for example, polyethylene, thermoplastic polyurethane, hytrel, etc.). While  FIG. 4  illustrates one exemplary embodiment of fiber optic cable  11 , one of ordinary skill in the art would recognize that fiber optic cable  11  may be realized using other configurations. 
       SUMMARY 
       [0010]    According to aspects of exemplary embodiments, there is provided: A small form-factor armored cable termination/fiber-optic seal which connects a fiber optic cable—including one or more armor wires and one or more cable tubes—to a pressure or splice housing, the armored cable termination/fiber-optic seal including: an armored termination which locks the one or more armor wires in a conical cavity; sealing paths which block water from traveling in the interstitial space between the one or more armor wires and the one or more cable tubes into the pressure housing; and fiber feed-through tubes which block water from traveling in the interior of the one or more cable tubes into the pressure housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Aspects of exemplary embodiments will be described in detail with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  illustrates a pressure housing with two armored cable termination/fiber-optic seal with overmold according to exemplary embodiments; 
           [0013]      FIG. 2  illustrates an isometric view of an armored cable termination/fiber-optic seal according to exemplary embodiments; 
           [0014]      FIG. 3  illustrates a cross-sectional view of armored cable termination/fiber-optic seal according to exemplary embodiments; 
           [0015]      FIG. 4  illustrates a fiber optic cable; 
           [0016]      FIG. 5  is a flow-chart illustrating a method of connecting cable  11  to pressure housing  10  of  FIG. 1  using armored cable termination/fiber-optic seal  12  of  FIGS. 2 and 3  according to exemplary embodiments. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0017]    Hereinafter, exemplary embodiments will be described in greater detail with reference to the accompanying drawings. 
         [0018]    In the following description, same reference numerals are used for the same elements when they are depicted in different drawings. Elements are described in detail in order to assist in an understanding of exemplary embodiments. Thus, it is apparent that exemplary embodiments may be carried out without those specifically-defined elements. Detailed descriptions of known elements are omitted. 
         [0019]      FIG. 1  illustrates a cable  11  connected to a pressure housing  10  according to exemplary embodiments. 
         [0020]    Referring to  FIG. 1 , cable  11  is cut to form cable  11  and cable  11 ′ each of which join pressure housing  10  on opposite ends of pressure housing  10  to form an in-line connection. Cable  11  is joined to pressure housing  10  by armored cable termination/fiber-optic seal  12 , the exterior portion of which may be covered by overmold  13 . Similarly, cable  11 ′ is joined to pressure housing  10  by armored cable termination/fiber-optic seal  12 ′, the exterior portion of which may be covered by overmold  13 ′. 
         [0021]      FIG. 1  shows an in-line installation where armored cable termination/fiber-optic seals  12  and  12 ′ are terminated onto cables  11  and  11 ′, respectively, and armored cable termination/fiber-optic seals  12  and  12 ′ are installed on opposite ends of pressure housing  10 . Depending on system design, however, other configurations are possible. For example, pressure housing  10  may accommodate more than one armored cable termination/fiber-optic seal  12  on one or more sides. 
         [0022]    Additionally, while  FIG. 1  shows overmolds  13  and  13 ′ covering armored cable termination/fiber-optic seals  12  and  12 ′, other configurations are again possible depending on system design. For example, one overmold  13  may cover cable  11 ′, cable termination/fiber-optic seal  12 ′, pressure housing  10 , and cable termination/fiber-optic seals  12 , and cable  11 . 
         [0023]    Overmold  13  may be, for example, polyurethane or polyethylene. Overmold  13  relieves the strain on cable  11  as it exits the bond with armored cable termination/fiber-optic seal  12 . Overmold  13  may also provide a water barrier at the point where cable  11  enters armored cable termination/fiber-optic seal  12  and/or where cable termination/fiber-optic seal  12  is affixed to pressure housing  10 . To maintain a strong bond and an effective water barrier, cable termination/fiber-optic seal  12  and/or pressure housing  10  may be covered in an adhesive (for example, an epoxy) before being covered by overmold  13  as described in more detail below. 
         [0024]      FIG. 2  illustrates an isometric view of armored cable termination/fiber-optic seal  12  according to exemplary embodiments. 
         [0025]    Referring to  FIG. 2 , an armored cable termination/fiber-optic seal  12  may include housing  20  which comprises interior barrel  21  and exterior barrel  22  separated by flange  23 . Armored cable termination/fiber-optic seal  12  may further include one or more fiber feed-through tubes  24 , retaining ring  25 , termination body  26 , O-ring grooves  27 , ribs  28 , helium leak test port  29 , and cable entry opening  30 . In this view, cable  11  and the overmold  12  are not shown. 
         [0026]    When armored cable termination/fiber-optic seal  12  is connected to pressure housing  10 , interior barrel  21  and the one or more fiber feed-through tubes  24  may be inserted inside pressure housing  10 . Flange  23  is used to mount armored cable termination/fiber-optic seal  12  onto the pressure housing  10  exterior. There are several possible O-ring seals between housing  20  of armored cable termination/fiber-optic seal  12  and the pressure housing  10 . One or more additional O-ring grooves may be machined into the flange  23  mating surface or machined into the pressure housing  10  mating surface. A crush O-ring (not pictured) may be added between the intersection of flange  23  and interior barrel  21 . The crush O-ring will be crushed as armored cable termination/fiber-optic seal  12  is secured onto pressure housing  10 . One or more barrel O-rings (not pictured) may be added to interior barrel  21  of the armored cable termination/fiber-optic seal  12 . These O-rings will be crushed as interior barrel  21  is installed in a pass through channel of pressure housing  10 . One or more ribs  28  (or knurls) are added to exterior barrel  22  to improve the shear strength between overmold  13  and pressure housing  10 . 
         [0027]      FIG. 3  is a cross-sectional view of armored cable termination/fiber-optic seal  12  according to exemplary embodiments. 
         [0028]    Referring to  FIG. 3 , armored cable termination/fiber-optic seal  12  may include termination body  26 , O-rings  31   a  and  31   b,  one or more of Morrison seals  32 , spacer  33  and  33 ′, and ground lug terminal  34 . Inside housing  20  is a conical-shaped void space referred to herein as conical cavity  35 . Inside conical cavity  35  sits wedge cone  36  which may include one or more tube paths  37  through which center tube  54  and one or more cables  53  may pass through. The exterior barrel  22  may include additional void spaces referred to herein as adhesive torsional lock feature keys  38  and cable entry shear features  39 . O-rings  31   a  and/or  31   b  may include back-up rings. 
         [0029]    Referring to  FIGS. 2 through 4 , fiber feed-through tubes  24  may be secured into termination body  26 . Each fiber feed-through tube  24  may be connected to termination body  26  using a Society of Automotive Engineers (SAE) seal. In an SAE seal, an O-ring is applied to the fiber feed-through tube  24 , which is threaded into termination body  26 . The fiber feed-through tubes  24  may be removably connected to termination body  26  to allows access to window strip cladding from optical fibers  55  during assembly of the armored cable termination/fiber-optic seal  12 . Fiber feed-through tubes  24  may include a 90-degree angled bevel  43  which allows for prevents shear strain and optical loss on optical fibers  55 . Retaining ring  25  may have a threaded collar to secure retaining ring  25  to interior barrel  21  of housing  20 . Retaining ring  25  may secure termination body  26  within interior barrel  21  of housing  20 . 
         [0030]    Fiber feed-through tube  24  may be filled with a water-resistant adhesive (for example, an epoxy such as a two-part urethane-based epoxy). Fiber feed-through tubes  24  eliminate any pressure differential on active optical fibers  55  and provides a barrier to stop water from entering pressure housing  10 . Fiber feed-through tubes  24  may be optimized with a 45-degree interior wall and the adhesive may be recessed inside fiber feed-through tube  24  to balance the shear and tensile properties of the adhesive. 
         [0031]    Cable  11  enters cable entry opening  30 . With cable sheath  51  removed, cable tubes  53  and  54  may be routed through tube paths  37 . One armor wire  52  is connected to ground lug terminal  34  to provide electrical continuity between armor wires  52 , pressure housing  10  and housing  20  of armored cable termination/fiber-optic seal  12 . 
         [0032]    The remaining armor wires  52  are straightened wrapped over the exterior of wedge cone  36 . 
         [0033]    An adhesive (for example, an epoxy such as ITW Socketfast or Hysol) may be used to lock wedge cone  36  and armor wires  52  in place (and form what is referred to herein as the “armor-wire-adhesive composite”). The taper angle of conical cavity  35  is designed to provide equal pressure along the wedge length against the armor-wire-adhesive composite. For example, the taper angle of conical cavity  35  may be equal to or greater than the taper angle of the armor-wire-adhesive composite. Therefore, when cable  11  is tensioned, force exerted by the armor-wire-adhesive composite on the conical cavity  35  (and vice versa) is distributed in a substantially equal manner. The armor-wire-adhesive composite provides a cable tension splice lock that exceeds the break strength of cable  11 . When cable  11  is tensioned, the armor-wire-adhesive composite prevents the armored cable termination/fiber-optic seal  12  from being the weakest link in the cable system. 
         [0034]    The roll-over geometry  42  of wedge cone  36  may reduce the length of wedge cone  36  without a reduction in strength. 
         [0035]    Adhesive torsional lock feature keys  38  and cable entry shear features  39  provide channels which are filled by the adhesive. These channels reduce the potential for rotation of the armor-wire-adhesive composite and cable. 
         [0036]    Cable tubes  53  and  54  are also routed through holes in the spacer  33  (also known as a tube guide). Spacer  33  is seated on the interior of housing  20  forming a void space between spacer  33  and the armor-wire-adhesive composite. This void space may be filled with an adhesive (for example, an epoxy such as polyurethane). Spacer  33  may include a cap portion  33 ′ made of a material known to bond to polyurethane (for example, Peek or Ultem). 
         [0037]    Elastomeric tubing may be applied over cable tubes  53  and  54  to form a band seal  41  which may be subsequently encapsulated when the void space is filled with an adhesive. Individual Morrison seals  32  provide a seal surrounding each cable tube  53  and  54 . O-rings  31   a  and  31   b  are located in O-ring grooves  27  and provide a redundant seal between armored cable termination/fiber-optic seal  12  and pressure housing  10 . Helium test port  29  allows for testing Morrison seals  32  and O-ring  31   a  during assembly. 
         [0038]    Termination body  26  provides an area in which the end of each cable tube  53  and  54  is separated from the water-resistant adhesive in fiber feed-through tube  24 . 
         [0039]    An adhesive (for example, an epoxy) may be applied to the exterior of housing  20  to prevent delamination of overmold  13  and housing  20  (similarly, if overmold  13  is applied over pressure housing  10 , an adhesive may be applied to the exterior of pressure housing  10  as well). The adhesive enters ribs  28 , which provide additional protection against shearing forces. Potting flow channels  40  may allow the adhesive applied to the exterior of housing  20  to enter housing  20  and provide an additional barrier against water entering pressure housing  10  and/or may allow the adhesive which forms the armor-wire-adhesive composite to enter the channel and provide additional torsional resistance. 
         [0040]    In the event that a cable sheath  51  is breached allowing water to bypass overmold  13 , water wicks past wedge cone  36  and the adhesive and band seals  41  form an additional barrier against water entering pressure housing  10 . In the event of a tube seal failure in the area of the adhesive and band seals  41 , Morisson seals  32  form a secondary barrier against water entering pressure housing  10 . In the event of a single tube failure without a breach of cable sheath  51 , each individual Morrison seal  32  acts to contain leakage, adhesive within fiber feed-through tubes  24  forms a barrier against water traveling in the interior of a tube into pressure housing  10  and O-ring  31   b  forms a barrier against water bypassing Morrison seals  32  and entering pressure housing  10 . In the event that one or more Morrison seal  32  fails, adhesive within fiber feed-through tubes  24  forms a barrier against water entering pressure housing  10 . In the event of a breach to cable sheath  51  and one of the cable tubes  53 , adhesive within fiber feed-through tubes  24  forms a barrier against water entering pressure housing  10  through the cable tube  53 . 
         [0041]    In the event that one of a plurality of cable tubes  53  and  54  is breached, the increased pressure causes any optical fibers  55  within the breached tube to experience optical degradation. Armored cable termination/fiber-optic seal  12 , however, may isolate each of the plurality of cable tubes  53  and  54  to prevent pressure increases and optical degradation within an unbreached cable tube  53  and  54 . 
         [0042]    The armored cable termination/fiber-optic seal  12  may be scalable to accommodate cable tubes  53  and  54  of varying diameters. 
         [0043]    Armored cable termination/fiber-optic seal  12  also provides an ability for cable tension testing, hydrostatic testing, and optical continuity testing before integration into a system. 
         [0044]      FIG. 5  is a flow-chart illustrating a method of connecting cable  11  of  FIG. 4  to housing  10  of  FIG. 1  through armored cable termination/fiber-optic seal  12  of  FIGS. 2 and 3  according to exemplary embodiments. 
         [0045]    Cable  11  is cut in operation S 1 . The end of cable  11  is prepared by removing a section of cable sheath  51  in operation S 2  and unwinding and straightening armor wires  52  and cable tubes  53  in operation S 3 . Central tube  54  of cable  11  is fed through tube path  42  of wedge cone  36  in operation S 4 . Wedge cone  36  and housing  20  is slid down cable  11  to a desired point in operation S 5 . 
         [0046]    In operation S 6 , the straightened armor wires  52  are wrapped over the exterior of wedge cone  36 . Armor wires  52  are cut in operation S 7 . One armor wire  52 , however, may be looped for future connection to housing  20  via ground lug terminal  34 . (Cable tubes  53  are left uncut.) 
         [0047]    In operation S 8 , housing  20  is slid up to wedge cone  36 . A capstan or press may be used to seat the armor wires  52  and wedge cone  36  inside housing  20 . An adhesive (for example, an epoxy such as ITW Socketfast or Hysol) may be used to lock wedge cone  36  and the composite of armor wires  52  and adhesive. The looped armor wire  52  is screwed into the ground lug terminal  38  in operation S 9 . 
         [0048]    In operation S 10 , a section of elastomeric tubing is applied over central tube  54  and cable tubes  53  to form a band seal  41 . Cable tubes  54  and  53  are routed through holes in the spacer/tube guide  33  which is seated on the interior of housing  20  to form a void space in operation S 11 . This void space is filled with an adhesive (for example, an epoxy such as polyurethane) in operation S  12 . This adhesive and the band seal  41  around the cable tubes  54  and  53  form a barrier against high pressure water if a leak develops at cable entry opening  30 . 
         [0049]    Cable tubes  53  and  54  are cut to length in operation S 13  and Morrison seals  32  comprising washers and elastomeric tubing is applied to cable tubes  53  and  54  in operation S 14 . Termination body  26  is pressed into housing  20  in operation S 15  and retaining ring  25  is used to locate and secure termination body  26  in operation S 16 . 
         [0050]    Fiber feed-through tubes  24  are applied to the assembly. The optical fibers  55  exiting the cut cable tubes  53  in termination body  26  are window stripped at a point corresponding to intersection of the fiber feed-through tube capillary and the  45  degree expansion in operation S 17 . Each fiber feed-through tube  24  is threaded into termination body  26  with an O-ring in operation S 18 . Fiber feed-through tube  24  is filled with an adhesive (for example, an epoxy) in operation S 19 . Armored cable termination/fiber-optic seal  12  is then connected to pressure housing  10  in operation S 20 . 
         [0051]    The foregoing description of the exemplary embodiments is intended to be illustrative. Many alternatives, modifications, and variations will be apparent to those skilled in the art. Descriptions and features listed in relation to the foregoing exemplary embodiments are not to be construed as limiting the present inventive concept, the scope of which is defined by the following claims.