Abstract:
A furcation tube for an optical fiber cable comprising a plurality of channels for receiving a plurality of optical fiber strands that allows for the breakout of multiple fiber groups without the need for marking individual fibers. For example, a 24 fiber cable can be broken out into two, 12-fiber groups within the same furcation tube for connectorization. This improves the sortabilility of the optical fiber strands and eliminates the extra bulk of using multiple furcation tubes. The furcation tube includes strength members disposed therein for strain relief.

Description:
RELATED APPLICATIONS 
       [0001]    This application is related to U.S. Provisional App. No. 61/318,966, filed Mar. 30, 2010, and entitled “Multiple Channel Optical Fiber Furcation Tube and Cable Assembly Using Same.” 
     
    
     FIELD 
       [0002]    The present invention relates to a protective casing for containing optical fiber strands, and more particularly, a furcation tube comprising multiple cavities that allow optical fiber strands to be routed into, through, and stored in smaller spaces. The protective casing allows optical fiber strands to fit therein while maintaining a relatively small footprint that can readily fit to select optical fiber connectors, providing the strength needed to protect the optical fiber strands, and allows forming of relatively small bend radii and winding on a reel without kinking and damaging the optical fibers. 
       BACKGROUND 
       [0003]    Optical fibers are widely used in a variety of applications, most notably in telecommunications, where optical fibers revolutionized the industry. Optical fibers are typically carried in fiber optic cables which range from one to as many as hundreds of optical fibers per cable. Normally, the fiber optic cable contains optical fiber strands in buffer tubes, either loose or in ribbon form. If a cable is to be joined to another cable or hardware in the field by connectors, it is common to attach the connectors to the cable at the factory before the cable is shipped to the installation site. This process is called “connectorization.” 
         [0004]    Fiber optic cable connectorization can be a very labor intensive process because the fiber optic connector is usually attached to each optical fiber in the fiber optic cable manually, one at a time. The manual process involves breaking out or “furcating” the optical fiber strands housed in the buffer tube or tubes inside the fiber optic cable using a buffer tube fanout insert assembly. For example, U.S. Pat. No. 5,231,688 discloses a furcation kit used to furcate the individual fibers from a cable for connectorization. After furcation, a connector is installed that requires precise techniques to insure quality. 
         [0005]    Optical cables comprising 12-strand groups have typically been used for connectivity in data centers. The optical fiber strands of a particular 12-strand group can be furcated using a single-channel furcation tube and thereby routed to a 12 fiber connector where the individual optical fibers are terminated in the connector. Typically, the connector is configured to receive the furcation tube and is coupled thereto. With the migration from 10 GbE systems to 40 GbE and 100 GbE systems there will be a need to transition to 24 fiber connectors for data transmission over parallel optics. Since standardized color coding provides for only 12 colors (without resorting to stripes, bands or additional indicia), using a conventional single-cavity furcation tube to accommodate 24 optical fiber strands will require 12 of the 24 strands to be separately marked so they can be sorted at the connector end. Moreover, using two single-cavity furcation tubes and feeding them into the back of the 24 fiber connector would be bulky and cumbersome, and is not a commercially attractive option. Thus, there is a need for a furcation tube sized to fit properly into the back of a conventional 24-strand connector that avoids the disadvantages of one or two single-cavity furcation tubes. 
       SUMMARY 
       [0006]    Furcation tubes are useful for the fanout of optical fiber strands from an optical fiber cable, allowing, among other things, for the connectorization of a cable length prior to shipping from the factory or warehouse to an end user. Prior art furcation tubes have been single channel tubes. Where an optical fiber cable contains optical fiber strands utilizing only 12 standard colors for coding, difficulties can arise when attempting to connectorize the cable with an optical fiber connector that accepts more than 12 colors. Whereas individual 12-strand color groups can be segregated within the cable via individual buffer tubes (e.g. one buffer tube for each group of twelve strands), if, for example, 24 optical fiber strands must be used with a single connector, the 24 strands utilizing 12 colors must be co-mingled within the same conventional single channel furcation tube to transition to the connector. This requires additional demarcation of the optical fiber strands to prevent confusion, or the use of several furcation tubes, one tube for each 12-strand group. Both approaches can be awkward. For example, the several single channel furcation tubes may not fit within the back side of the optical fiber connector. 
         [0007]    To overcome these difficulties, a furcation tube comprising multiple channels for loosely receiving a plurality of optical fiber strands is disclosed. By loosely receive what is meant is that the optical fiber strands contained within each channel of the furcation tube are free to move within that channel. Additionally, the furcation tube includes one or more additional channels that hold strength members for relieving strain on the optical fiber strands when the strands are connectorized. The strength members may comprise, for example, a polymeric yarn like aramid. 
         [0008]    In accordance with one embodiment, a furcation tube for connectorizing an optical fiber cable is described, the furcation tube comprising a first end and a second end, and further comprising a partition member, a protective jacket disposed about the partition member, and wherein the partition member defines a plurality of longitudinal fiber channels extending from the first end to the second end of the furcation tube, each of the fiber channels sized to loosely receive at least twelve optical fiber strands having an individual outside diameter of at least about 235 μm each, and wherein the partition member further defines a plurality of longitudinal strength member channels extending from the first end to the second end, each strength member channel including one or more strength members disposed loosely therein. The furcation tube is sized to accommodate at least two optical fiber channels having a cross sectional area that is at least 1 mm 2  each. For example, the furcation tube may have an outside diameter in the range between about 2.8 mm and 5.6 mm, preferably in the range between about 2.8 mm and 3.3 mm. 
         [0009]    The strength members preferably comprise a polymeric yarn. In some embodiments the partition member comprises web portions, wherein an intersection between adjacent web portions forms a radius. The web portions may be, for example, substantially planar walls or fins. The partition member may comprise two V-shaped web portions connected to and separated by a central web portion. In some embodiments an angle between substantially planar web portions bounding a strength member channel is in a range between about 60 degrees and about 90 degrees. Preferably a cross sectional shape of the furcation tube is substantially circular. 
         [0010]    In another embodiment a connectorized optical fiber cable assembly is disclosed comprising an optical fiber cable comprising a plurality of optical fiber strands, a furcation tube having a first end and a second end, the furcation tube comprising a partition member and the first end being coupled to a free end of the optical fiber cable and. The partition member forms a plurality of longitudinal fiber channels extending from the first end of the furcation tube to the second end of the furcation tube, each of the fiber channels loosely containing at least twelve optical fiber strands from the optical fiber cable, the optical fiber strands having an individual outside diameter of at least 235 μm each, and wherein the partition member further forms at least one longitudinal strength member channel extending from the first end of the furcation tube to the second end of the furcation tube. The at least one strength member channel includes one or more strength members disposed loosely therein. The one or more strength members may comprise, for example, a polymeric yarn. The partition member can include substantially planar web portions. An intersection between adjacent web portions can be manufactured to form a radius. The partition member may comprise two V-shaped web portions connected to and separated by a central web portion. An angle between substantially planar web portions bounding a strength member channel is preferably in a range between about 60 degrees and about 90 degrees. 
         [0011]    A cross sectional area of each fiber channel is at least 1 mm 2 . 
         [0012]    An optical fiber connector is coupled to the second end of the furcation tube. In some embodiments a protective jacket is disposed about the partition member. Preferably, a cross sectional shape of the furcation tube is substantially circular. An outside diameter of the furcation tube can be in the range between about 2.8 mm and 5.6 mm, preferably between about 2.8 and 3.3 mm. 
         [0013]    In certain embodiments the furcation tube is un-jacketed, and the plurality of fiber channels are enclosed within the partition member along a length of the partition member. That is, each fiber channel is embedded within the partition member and is open only at the furcation tube ends. The partition member may further include a plurality of strength member channels, each strength member channel being enclosed within the partition member along a length of the partition member. 
         [0014]    Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. It is to be understood that the various features of the invention disclosed in this specification and in the drawings can be used in any and all combinations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a perspective view of a furcation tube according to an embodiment of the present invention; 
           [0016]      FIG. 2  is a cross sectional view of an exemplary optical fiber strand; 
           [0017]      FIG. 3  is a cross sectional view of a furcation tube according to an embodiment of the present invention; 
           [0018]      FIG. 4  is a cross sectional view of a furcation tube according to another embodiment of the present invention; 
           [0019]      FIG. 5  is a cross sectional view of a furcation tube according to another embodiment of the present invention; 
           [0020]      FIG. 6  is a cross sectional view of a furcation tube according to another embodiment of the present invention; 
           [0021]      FIG. 7  is a cross sectional view of a furcation tube according to another embodiment of the present invention; 
           [0022]      FIG. 8  is a cross sectional view of a furcation tube according to another embodiment of the present invention; 
           [0023]      FIG. 9  is a cross sectional view of a furcation tube according to another embodiment of the present invention; 
           [0024]      FIG. 10  is a cross sectional view of a furcation tube according to another embodiment of the present invention; 
           [0025]      FIG. 11  is a cross sectional view of a furcation tube according to another embodiment of the present invention; 
           [0026]      FIG. 12  is a cross sectional view of an exemplary optical fiber cable; 
           [0027]      FIG. 13  is a side view of a connectorized optical fiber cable assembly according to an embodiment of the present invention. 
           [0028]      FIG. 14  is a side view of a connectorized optical fiber cable assembly having more than one furcation tube coupled to the optical fiber cable according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to one having ordinary skill in the art, having had the benefit of the present disclosure, that the present invention may be practiced in other embodiments that depart from the specific details disclosed herein. Moreover, descriptions of well-known devices, methods and materials may be omitted so as not to obscure the description of the present invention. Finally, wherever applicable, like reference numerals refer to like elements. 
         [0030]      FIGS. 1 and 2  depict an embodiment of furcation tube  10  comprising protective jacket  12  and a plurality of cavities or channels formed by partition member  14 . For example, furcation tube  10  may comprise at least two channels  16   a  and  16   b  that extend along the length of the furcation tube, the channels being sized to loosely receive multiple optical fiber strands. That is, channels  16   a  and  16   b  are sized so the optical fiber strands can move freely with respect to protective jacket  12  and partition member  14 . For example, each channel  16   a  and  16   b  can be sized to loosely contain at least twelve optical fiber strands having an outside diameter of between 235 and 265 μm, nominally between about 245 μm to about 255 μm. Thus, the cross sectional area of each channel  16   a  and  16   b  in a plane perpendicular to the longitudinal axis of furcation tube  10  should be at least about 1 mm 2 , but in any case should provide for a packing density in a single channel (i.e. channel  16   a  or channel  16   b ) of approximately 60% when the channel contains twelve optical fiber strands having a nominal outside diameter of up to 265 μm. Consequently, at least a portion of the volume of each channel  16   a ,  16   b  is not filled by the optical fiber strands. 
         [0031]    An outside diameter OD of the furcation tube (see  FIG. 4 ) is preferably in the range between about 2.8 mm and 5.6 mm, more preferably between about 2.8 mm and about 3.3 mm. A nominal protective jacket thickness t is preferably between about 0.25 mm and about 0.35 mm, with a typical protective jacket thickness of about 0.3 mm. To aid in maintaining a small outside diameter of furcation tube  10 , the protective jacket preferably consists of only a single jacket layer, however additional layers can be used if desired. The small outside diameter of the furcation tube helps alleviate congestion within an equipment rack. Additionally, furcation tube  10  is preferably substantially circular to more easily facilitate coupling of the furcation tube to a connector, but can be formed to have other shapes if desired. 
         [0032]    An exemplary cross sectional illustration of an optical fiber strand  18  that can be used with the present furcation tube is shown in  FIG. 3 . Optical fiber strand  18  comprises an optical fiber  20  including core portion  22  and cladding portion  24 . Optical fiber  20  is preferably coated with one or more layers of a polymeric protective coating material such as an acrylate. As shown in  FIG. 3 , optical fiber  20  is coated with a soft polymeric inner primary coating  26  and a harder polymeric outer secondary coating  28 . Optical fiber  20  may be plastic or glass but is more commonly glass. Thus, core portion  22  and cladding portion  24  are preferably glass. However, in some embodiments core portion  22  and cladding portion  24  may be formed from plastic, and in certain other embodiments, core portion  22  may be glass and cladding portion  24  may be formed from plastic. As described, the outside diameter of optical fiber strand  18  is typically at least about 235 μm, and preferably in the range from about 235 μm to about 265 μm. A typical outside diameter can be, for example, about 250 μm. 
         [0033]    Furcation tube  10  may further comprise one or more additional channels that extend along the length of the furcation tube, the additional channels being sized to receive strength members. For example, according to the embodiment of  FIG. 4  depicting a cross sectional view of a furcation tube  10 , the furcation tube comprises two channels  16   a  and  16   b  sized to loosely receive a plurality of optical fiber strands, and two additional channels  30   a  and  30   b  sized to receive one or more strength members  32 , such as polymeric yarns. The yarns may, for instance, be aramid yarns, but may also be formed from any other suitable material such as fiberglass or polyester. The yarns may have a denier in the range from about 250 to about 3000. A typical denier is about 1420. According to the present embodiment and as shown in  FIG. 4 , two strength member, e.g. yarns, are included in each of channels  30   a  and  30   b . Each yarn may comprise hundreds of individual filaments. Strength members  32  provide longitudinal strength to the furcation tube, and may also serve as anchoring points to relieve strain on the jacket and/or partition member, and in particular the optical fiber strands. Since threading strength yarns from the cable to be connectorized through the furcation tube can be difficult, the yarns are preferably deposited in additional channels  30   a  and  30   b  when the furcation tube is formed, e.g. during an extrusion process. 
         [0034]    As also indicated in  FIG. 4 , channels  16   a ,  16   b  and  30   a ,  30   b  are defined by partition member  14  within the interior space of defined by jacket  12 . Partition member  14  is an extruded member formed from a suitable thermoplastic. Suitable materials include, but are not limited to PVC, PE, PP, PBT, FRPE, FEP, ETFE and PTFE. Preferably the material from which the partition member is formed has a low surface friction to allow the optical fibers to slide easily through the channels. Method of extruding complex polymeric shapes are well known and will not be covered here. 
         [0035]    As shown in  FIG. 4 , partition member  14  may, in some embodiments, be generally in the shape of an “X” (cruciform). For example, the partition member of  FIG. 4  has an “X” shape formed by intersecting web portions  38   a - 38   d . As shown, web portions  38   a - 38   d  intersect each other at sharp angles. The web portions have a nominal thickness of about 0.2 mm. In some embodiments, the web portions are substantially planar. However, it should be recognized that the web portions can be formed into different shapes, such as curved, or having multiple segments. In other embodiments, such as the embodiment shown in  FIG. 5 , the web portions may have a radius formed at their intersection points. A radius of between about 0.2 and 0.3 mm has been found to be adequate. For example, a nominal radius of 0.25 can be used. In still other embodiments, such as the embodiment of  FIG. 6 , the partition member includes central web portion  38   e  separating fiber channels  16   a  and  16   b . In this instance, web portions  38   a - 38   d  extend outward from ends of the central web  38   e  to the inside surface of the furcation tube jacket. 
         [0036]    In still another embodiment illustrated in  FIG. 7 , furcation tube  10  comprises channels  16   a  and  16   b  for loosely receiving a plurality of optical fiber strands  18 , and a single channel  30  containing one or more strength members  32  formed by a “Y” shaped partition member  14 . In the orientation depicted, the “Y” is formed by one web portion forming the downward leg of the “Y”, and two additional web portions in the form of a “V” that intersect with the downward leg. As in the previous embodiments, partition member  14  and strength members  32  are surrounded by jacket  12 . 
         [0037]    In accordance with the embodiment shown in  FIG. 8 , partition member  14  is formed without web portions, and is instead a generally solid body with the exception that the one or more channels containing strength members  32  extend longitudinally through the partition member. In cross sectional aspect, the partition member according to the present embodiment appears as a filled in or solid “X” shape (with the exception of the strength member channels). In contrast to the previous embodiments, strength member channels  30   a  and  30   b  according to the embodiment of  FIG. 8  are not open along their longitudinal extent, but instead are contained entirely within the partition member, having openings only at the ends of the furcation tube. However, similar to the previous embodiments, channels  16   a  and  16   b  for loosely receiving a plurality of optical fiber strands are formed between the partition body and jacket  12 . 
         [0038]    In still other embodiments, furcation tube  10  may be formed without jacket  12 , and include only partition member  14 . In the embodiments of  FIGS. 9-11 , partition member  14  defines a pair of channels or cavities  16   a ,  16   b  for loosely receiving a plurality of optical fiber strands, and at least one channel containing one or more strength members.  FIG. 9 , for example, depicts furcation tube  10  comprising channels  16   a  and  16   b  for loosely receiving a plurality of optical fiber strands, for example at least 12 optical fiber strands per channel, and a single channel  30  containing at least one strength member  32 , and in this instance a plurality of strength members (e.g. four). Partition member  14  includes a substantially circular cross section in a plane perpendicular to the longitudinal dimension of the partition member. In the embodiment of  FIG. 10 , partition member  14  includes two channels  30   a  and  30   b  containing at least one strength member  32  each, and in this instance, two strength members  32  each. The embodiment according to  FIG. 11  is identical to the embodiment of  FIG. 10  except that a cross sectional shape of the partition member is non-circular (e.g. oval) rather than substantially circular. 
         [0039]    Furcation tube  10  may be used by itself or as a part of a cable  40  or other assembly. A cross sectional view of an exemplary optical fiber cable is shown in  FIG. 12 , the optical fiber cable comprising an inner buffer tube  42  forming interior cavity  44  and containing a plurality of optical fiber strands  18 , one or more cable strength members  46 , and a cable sheath  48  that provides mechanical protection to buffer tube  42  and the optical fiber strands within. In the exemplary optical fiber cable of  FIG. 12 , optical fiber cable strength member  46  is shown as polymer yarns or filaments disposed between buffer tube  42  and cable sheath  48 . It should be understood however that the furcation tubes disclosed herein may be used with a myriad of different cable designs, and the exemplary optical fiber cable of  FIG. 12  should not be viewed is limiting in this respect. 
         [0040]    Typically, furcation tubes  10  are attached to an optical fiber cable, such as the cable of  FIG. 12 , to break out and transition the optical fiber strands therein to a connector. That is, the furcation tube is used to connectorize the cable.  FIG. 13  depicts furcation tube  10  used for such a purpose, wherein a first end  50  (see  FIG. 1 ) of furcation tube  10  is affixed to optical cable  40  via plug  52 . To appropriately route the optical fibers from the fiber optic cable to the connectors, plug  52  may be used to control and manage the one or more furcation tube containing the optical fiber strands. The plug may be a pre-molded article having specific holes for inserting one or more furcation tubes, such as an injection molded article formed from a thermoplastic, or the plug may be a customized article formed at the time the optical fiber cable is connectorized with one or more connectors by filling a disposable mold with an epoxy adhesive. Plug  52  affixes the one or more furcation tubes to the cable, anchors the furcation tube strength members  32  at the cable end, and protects the optical fiber strands at the transition from cable buffer tube  42  to furcation tube  10 . 
         [0041]      FIG. 13  illustrates one embodiment of plug  52  formed using an epoxy adhesive. While  FIG. 13  shows only a single furcation tube, it should be understood that multiple furcation tubes may be embedded within the plug. To form the assembly shown in  FIG. 13 , a length of cable sheath  48  is removed from cable  40 , exposing any buffer tubes (e.g. buffer tube  42 ) that contain optical fiber strands and cable strength members  46  contained within the cable. Lengths of the cable buffer tubes are also removed, leaving the optical fiber strands exposed at the end of the cable. The cable sheath removal length and cable buffer tube lengths required at the end of the cable are based on the specific installation requirements. The cable strength members are removed as close as necessary to the cable sheath end. To ensure adequate stress relief of the cable at the epoxy, the strength members  46  of the cable may be exposed, and fanned out and back around the cable jacket so the ends of strength members  46  are embedded within the epoxy plug when it cures. 
         [0042]    A length of flexible tubing (not shown) that serves as a mold, such as vinyl heat shrink tube, is slid over the end of the cable from which the sheath was removed, and the optical fiber strands are threaded through the appropriate channels or cavities  16   a ,  16   b  of furcation tube  10  with the first end of the furcation tube within the vinyl molding tube. The vinyl molding tube is clamped to the cable sheath at the far end of the vinyl molding tube (farthest from the cable end to be connectorized), such as by a hose clamp, and the cavity formed by the vinyl tube filled with an epoxy adhesive. When the epoxy is cured, the vinyl molding tube is sliced open and removed, leaving furcation tube  10  anchored within the thus formed epoxy plug  52 . To ensure adequate stress relief of the optical fiber connector attached to the second end of the furcation tube, the strength members  32  of the furcation tube may be exposed at the first end  50  of furcation tube  10 , and fanned out and back around furcation tube end so the ends of strength members  32  are embedded within the epoxy plug when it cures. Following attachment of furcation tube  10  to cable  40  via plug  52 , optical fiber connector  54  (e.g. a multi-fiber optical connector) is attached to second end  56  of furcation tube  10  according to conventional methods, and anchored thereto via the furcation tube strength members. For example, furcation tube  10  can be threaded through connector boot  58  and secured to connector  54  via a crimp ring (not shown) that crimps the furcation tube (and the strength members) to the connector. 
         [0043]      FIG. 14  depicts a fiber optic cable assembly comprising a plurality of furcation tubes  10 . 
         [0044]    It should be emphasized that the above-described embodiments of the present invention, particularly any “preferred” embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.