Patent Publication Number: US-9891397-B2

Title: Multi-fiber, fiber optic cables and cable assemblies providing constrained optical fibers within an optical fiber sub-unit

Description:
PRIORITY APPLICATIONS 
     This application is a continuation under 35 U.S.C. § 120 of U.S. patent application Ser. No. 14/494,851, filed on Sep. 24, 2014, which is a continuation of U.S. patent application Ser. No. 13/165,974, filed on Jun. 22, 2011. The content of each of these applications is relied upon and incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Field of the Disclosure 
     The technology of the disclosure relates to multi-fiber, fiber optic cables, and related fiber optic components and assemblies. 
     Technical Background 
     Benefits of optical fiber use include extremely wide bandwidth and low noise operation. Because of these advantages, optical fiber is increasingly being used for a variety of applications, including but not limited to broadband voice, video, and data transmission. As a result, fiber optic communications networks include a number of interconnection points at which multiple optical fibers are interconnected. Fiber optic communications networks also include a number of connection terminals, examples of which include, but are not limited to, network access point (NAP) enclosures, aerial closures, below grade closures, pedestals, optical network terminals (ONTs), and network interface devices (NIDs). In certain instances, the connection terminals include connector ports, typically opening through an external wall of the connection terminal. The connection terminals are used to establish optical connections between optical fibers terminated from the distribution cable and respective optical fibers of one or more pre-connectorized drop cables, extended distribution cables, tether cables or branch cables, collectively referred to herein as “drop cables.” The connection terminals are used to readily extend fiber optic communications services to a subscriber. In this regard, fiber optic networks are being developed that deliver “fiber-to-the-curb” (FTTC), “fiber-to-the-business” (FTTB), “fiber-to-the-home” (FTTH) and “fiber-to-the-premises” (FTTP), referred to generically as “FTTx.” 
     Use of multi-fiber distribution cables in a fiber optic communications network can present certain challenges. For example, excessive optical skew or delay can cause transmission errors. Optical fibers in multi-fiber distribution cables can be damaged if the cable is subject to excessive bending. To prevent or reduce excessive bending, cable strength members may be disposed within a cable jacket of the fiber optic cable along with the optical fibers. However, the optical fibers may engage and become entangled with the strength members thereby bending the optical fibers inside the cable jacket and attenuating the optical signals carried on the optical fibers. Further, a terminated end of the distribution cable often times must be pulled to a desired location during installation, such as to a connection terminal (e.g., a fiber distribution hub (FDH)) or to another distribution cable, through relatively small diameter conduits. Accordingly, a terminated end of the distribution cable can be provided within a pulling grip. When pulled, the pulling grip is capable of transferring a tensile load (e.g., a pulling load) to the cable jacket and/or strength members of the fiber optic cable. However, a portion of the pulling load may be transferred to the optical fibers within the fiber optic cable. Transferring excessive load to optical fibers disposed in a fiber optic cable can damage the optical fibers. 
     SUMMARY 
     Embodiments disclosed in the detailed description include multi-fiber, fiber optic cables providing constrained optical fibers within an optical fiber sub-unit disposed in a cable jacket. Related fiber optic components and fiber optic assemblies are also disclosed. In one embodiment, one or more optical fiber sub-units can be provided that each comprises a plurality of optical fibers disposed adjacent one or more sub-unit strength members within a sub-unit jacket. Movement of optical fibers within a sub-unit jacket is constrained by an interior wall of the sub-unit jacket and/or the sub-unit strength members disposed in the sub-unit jacket. In this manner as a non-limiting example, optical fibers disposed in an optical fiber sub-unit can be held together as a unit within the optical fiber sub-unit. By providing the optical fibers constrained as a unit in optical fiber sub-units, the optical fiber sub-units may be constrained in a furcation assembly without having to expose the optical fibers within the optical fiber sub-units, thereby reducing complexity in fiber optic cable assembly preparations. Avoiding exposing optical fibers in a furcation assembly may also reduce the risk of damaging the optical fibers during furcation assembly preparations. Constraining the optical fibers within the optical fiber sub-units may also, as non-limiting examples, provide low optical skew, may reduce or eliminate entanglement between the optical fibers and the cable strength members to reduce or avoid optical attenuation, and/or may allow the optical fibers to act as anti-buckling components within the fiber optic cable. 
     As one non-limiting option, the optical fiber sub-units may be disposed adjacent to the cable strength members within the cable jacket in a manner that allows movement between the optical fiber sub-units and the cable strength members within the cable jacket. In this manner, the one or more optical fiber sub-units can freely move within the cable jacket in this embodiment. As a result in one non-limiting example, entanglements between the cable strength member and the optical fiber sub-units that may cause optical attenuation or broken fibers may be avoided. Stranding can cause a bend to be disposed in the optical fiber sub-units thereby attenuating optical signals carried by the optical fibers in the optical fiber sub-units. 
     In this regard in one embodiment, a fiber optic cable assembly is disclosed. This fiber optic cable assembly comprises a fiber optic cable comprising a cable jacket, one or more cable strength members disposed within the cable jacket, and one or more optical fiber sub-units disposed within the cable jacket. This fiber optic cable assembly also comprises an end portion of the fiber optic cable comprising end portions of optical fiber sub-units and end portions of the cable strength members both exposed from an end portion of the cable jacket. This fiber optic cable assembly also comprises a furcation assembly receiving the end portion of the fiber optic cable at a first end of the furcation assembly. The furcation assembly terminates the end portion of the cable jacket and the end portions of the cable strength members. The end portions of the optical fiber sub-units extending through and from a second end of the furcation assembly. Additionally, each of the optical fiber sub-units may comprise a plurality of optical fibers and one or more sub-unit strength members disposed adjacent to each other in a sub-unit jacket. In this regard, movement of the optical fibers within the sub-unit jacket is constrained by an interior wall of the sub-unit jacket and the sub-unit strength members. 
     In this embodiment, the one or more cable strength members are disposed within the cable jacket in a first length, and the one or more optical fiber sub-units are disposed within the cable jacket in a second length, the second length greater than the first length. In this manner as a non-limiting example, a tensile load (e.g., a pulling load) placed on the furcation assembly is directed more to the one or more cable strength members to avoid or reduce stress placed on the optical fibers. As a non-limiting option in this embodiment, the optical fiber sub-units are disposed adjacent to the cable strength members within the cable jacket that allows movement between the one or more optical fiber sub-units and the one or more cable strength members within the cable jacket. As another non-limiting example, the optical fiber sub-units can include tight buffered optical fibers that are disposed adjacent to strength members disposed within the sub-unit jackets, wherein movement between is allowed between the optical fiber sub-units and the one or more cable strength members within the cable jacket of the fiber optic cable. 
     In another embodiment, a method of assembling a fiber optic cable is disclosed. This method comprises disposing one or more cable strength members within a cable jacket of a fiber optic cable in a first length. This method also comprises disposing one or more optical fiber sub-units within the cable jacket in a second length, the second length greater than the first length, and each optical fiber sub-unit including a sub-unit jacket and a plurality of optical fibers disposed within the sub-unit jacket. This method also comprises exposing end portions of the one or more optical fiber sub-units and end portions of the one or more cable strength members from an end portion of the cable jacket. This method also comprises receiving the end portion of the fiber optic cable at a first end of a furcation assembly. This method also comprises terminating the end portion of the cable jacket and the end portions of the one or more cable strength members in the furcation assembly. 
     In another embodiment, a fiber optic cable is disclosed. This fiber optic cable comprises a cable jacket. This fiber optic cable also comprises one or more cable strength members disposed within the cable jacket in a first length. This fiber optic cable also comprises one or more optical fiber sub-units disposed within the cable jacket in a second length, the second length greater than the first length. Each of the optical fiber sub-units comprises a plurality of optical fibers and one or more sub-unit strength members disposed adjacent to each other in a sub-unit jacket. In this regard, movement of the optical fibers within the sub-unit jacket is radially constrained by an interior wall of the sub-unit jacket and the sub-unit strength members, and the plurality of optical fibers are in friction contact with the one or more sub-unit strength members constraining relative longitudinal movement of the plurality of optical fibers within the sub-unit jacket. The optical fiber sub-units are disposed adjacent to the cable strength members within the cable jacket. The one or more optical fiber sub-units are disposed within the cable jacket adjacent to the one or more cable strength members to allow movement between the one or more optical fiber sub-units and the one or more cable strength members within the cable. 
     In any of the embodiments disclosed herein, the optical fiber sub-units can be tight buffered optical fibers without the inclusion of strength members provided within the optical fiber sub-unit(s), if desired. 
     Additional features and advantages will be 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 embodiments as described herein, including the detailed description that follows, the claims, as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is an end view of a cross-section of an exemplary multi-fiber, fiber optic cable comprised of a plurality of optical fiber sub-units disposed within a cable jacket, each of the plurality of optical fiber sub-units comprising a plurality of optical fibers and one or more sub-unit strength members disposed in a sub-unit jacket; 
         FIG. 2  is an end view of a cross-section of one optical fiber sub-unit disposed inside the cable jacket of the fiber optic cable in  FIG. 1 ; 
         FIG. 3  is a top perspective view of an exemplary fiber optic cable assembly comprised of a portion of end portions of the optical fiber sub-units (“optical fiber sub-unit end portions”) and a portion of end portions of cable strength member(s) (“cable strength member end portion(s)”) exposed from the cable jacket of an end portion of the fiber optic cable of  FIG. 1  secured inside a furcation plug of a furcation assembly; 
         FIG. 4  illustrates an end portion of the fiber optic cable in  FIG. 1  cut to a desired length with a portion of an end portion of the cable jacket removed to expose the optical fiber sub-unit end portions and cable strength member end portions from the end portion of the cable jacket to prepare for providing the furcation assembly, including the furcation plug in  FIG. 3 ; 
         FIG. 5  is a schematic side view of a cross-section of the fiber optic cable assembly in  FIG. 3  illustrating the optical fiber sub-units disposed in the cable jacket of the fiber optic cable adjacent to the one or more cable strength members to allow movement between the one or more optical fiber sub-units and the one or more cable strength members within the cable jacket; 
         FIG. 6  is a schematic side view of a cross-section of the fiber optic cable assembly of  FIG. 3  illustrating an optional exemplary strain relief member and optional exemplary spiral-wound tubing securing the optical fiber sub-units; 
         FIG. 7  is a top perspective view of the fiber optic cable assembly in  FIG. 3 , wherein the furcation plug is arranged to be enclosed with an exemplary pulling grip sub-assembly for pulling the fiber optic cable; 
         FIG. 8  illustrates the fiber optic cable assembly in  FIG. 7  with the furcation plug enclosed in the pulling grip sub-assembly and enclosed in an exemplary pulling bag for pulling the fiber optic cable; 
         FIG. 9  is a top perspective view of the fiber optic cable assembly of  FIG. 3  with an alternative exemplary furcation plug; 
         FIG. 10A  illustrates an alternative fiber optic cable assembly comprised of optical fiber sub-unit end portions and cable strength member end portion(s) exposed from the cable jacket of an end portion of the fiber optic cable of  FIG. 1 , wherein a cable strength member pulling loop is formed from disposing and securing a loop disposed in the cable strength member end portion on the cable jacket; 
         FIG. 10B  illustrates the fiber optic cable assembly in  FIG. 10A  with the cable strength member pulling loop fully assembled; 
         FIG. 11  illustrates the fiber optic cable assembly in  FIGS. 10A and 10B , wherein the cable strength member pulling loop is not disposed in a strength member tube; 
         FIG. 12  illustrates an alternate exemplary fiber optic cable assembly comprised of a cable strength member pulling loop formed by disposing the cable strength member end portion through first and second heat shrink tubes and looping the end of the cable strength member end portion back through the first heat shrink tube adjacent to the cable jacket; 
         FIG. 13  illustrates the cable strength member pulling loop of the fiber optic cable assembly in  FIG. 12  with the exposed cable strength member end portion trimmed and fanned around the cable jacket of the fiber optic cable; 
         FIG. 14  illustrates disposing a cable jacket heat shrink tube over the cable strength member pulling loop in the fiber optic cable assembly in  FIG. 13  to form an exemplary cable strength member pulling loop; and 
         FIG. 15  illustrates the cable strength member pulling loop in the fiber optic cable assembly in  FIG. 14  after exposing the cable jacket heat shrink tube to secure the cable strength member pulling loop to the cable jacket. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the concepts may be embodied in many different forms and should not be construed as limiting herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts. 
     Embodiments disclosed in the detailed description include multi-fiber, fiber optic cables providing constrained optical fibers within an optical fiber sub-unit disposed in a cable jacket. Related fiber optic components and fiber optic assemblies are also disclosed. In one embodiment, one or more optical fiber sub-units can be provided that each comprises a plurality of optical fibers disposed adjacent one or more sub-unit strength members within a sub-unit jacket. Movement of optical fibers within a sub-unit jacket is constrained by an interior wall of the sub-unit jacket and/or the sub-unit strength members disposed in the sub-unit jacket. In this manner as a non-limiting example, optical fibers disposed in an optical fiber sub-unit can be held together as a unit within the optical fiber sub-unit. By providing the optical fibers constrained as a unit in optical fiber sub-units, the optical fiber sub-units may be constrained in a furcation assembly without having to expose the optical fibers within the optical fiber sub-units, thereby reducing complexity in fiber optic cable assembly preparations. Avoiding exposing optical fibers in a furcation assembly may also reduce the risk of damaging the optical fibers during furcation assembly preparations. Constraining the optical fibers within the optical fiber sub-units may also, as non-limiting examples, provide low optical skew, may reduce or eliminate entanglement between the optical fibers and the cable strength members to reduce or avoid optical attenuation, and/or may allow the optical fibers to act as anti-buckling components within the fiber optic cable. 
     In this regard,  FIG. 1  is an end view of a cross-section of one exemplary multi-fiber, fiber optic cable  10 . The fiber optic cable  10  may be used as a distribution cable or drop cable as non-limiting examples. With continuing reference to  FIG. 1 , the fiber optic cable  10  is comprised of a plurality of optical fiber sub-units  12  disposed longitudinally within a cable jacket  14 .  FIG. 2  is an end view of a cross-section of one optical fiber sub-unit  12  disposed inside the cable jacket  14  of the fiber optic cable  10  in  FIG. 1 . With reference back to  FIG. 1 , the plurality of optical fiber sub-units  12  are disposed in the cable jacket  14 , but only one optical fiber sub-unit  12  could be disposed in the cable jacket  14  if desired as well. Each optical fiber sub-unit  12  disposed in the cable jacket  14  of the fiber optic cable  10  in this embodiment includes a plurality of optical fibers  16  disposed within a sub-unit jacket  18 . The optical fibers  16  may be buffered or not buffered. As a non-limiting example, twelve (12) optical fibers  16  may be disposed within each sub-unit jacket  18  of each optical fiber sub-unit  12  to provide multi-fibered optical fiber sub-units  12 . Any number of the optical fibers  16  may be disposed in each optical fiber sub-unit  12 . Further, different optical fiber sub-units  12  may contain different counts of optical fibers  16 , if desired. As will be discussed in more detail below, end portions of the optical fibers  16  may be connectorized or pre-connectorized with fiber optic connectors for establishing fiber optic connections with the optical fibers  16  in the fiber optic cable  10 . 
     With continuing reference to  FIG. 1 , a cable strength member  20  is also disposed longitudinally inside the cable jacket  14  adjacent to the optical fiber sub-units  12 . The cable strength member  20  provides strength support in the fiber optic cable  10  to resist excessive elongation to prevent or reduce the risk of damage to the optical fibers  16  and/or to reduce or avoid optical attenuation. One or more cable strength members  20  may be disposed inside the cable jacket  14 . As a non-limiting example, the cable strength member  20  may be provided as one or more tensile yarns. As another non-limiting example, the cable strength member  20  may be manufactured from aramid, such as Kevlar®. Other examples of materials that may be employed for the cable strength member  20  include, but are not limited to fiberglass, ultra high molecular weight polyethylene (UHMWPE) such as Dyneema® for example, paraaramid copolymers such as Technora® for example, or other such tensile yarns. 
     With continuing reference to  FIG. 1 , in this embodiment, the optical fiber sub-units  12  are optionally loosely disposed in the cable jacket  14  adjacent to the cable strength member  20 . In this manner, the optical fiber sub-units  12  can move between each other and with respect to the cable strength member  20  and the cable jacket  14 . In one embodiment, the optical fiber sub-units  12  may be exposed from the cable jacket  14  to provide furcation legs from the fiber optic cable  10 . Disposing the optical fiber sub-units  12  loosely in the cable jacket  14  can allow for a furcation assembly that directs a tensile load (e.g., a pulling load) primarily to the cable strength member  20  and/or the cable jacket  14  as opposed to the optical fiber sub-units  12  to protect the optical fibers  16  from damage. As another non-limiting example, disposing the optical fiber sub-units  12  loosely within the cable jacket  14  may also avoid the need for stranding between the optical fiber sub-units  12  and the cable strength member  20 , which can reduce manufacturing complexity. Stranding may also cause the cable strength members  20  to be longer than the optical fiber sub-units  12  such that tensile loads applied to the fiber optic cable  10  are firstly or primarily borne by the optical fiber sub-units  12  and then secondly or secondarily by the cable strength member  20 . The cable strength member  20  may also be disposed loosely within the cable jacket  14  to allow further freedom of relative movement between the optical fiber sub-units  12  and the cable strength member  20  within the cable jacket  14 . 
     With continuing reference to  FIG. 1 , an inner diameter ID 1  of the cable jacket  14  may be greater than an outer diameter OD 1  of the collective grouping of the optical fiber sub-units  12  and cable strength member  20  disposed inside the cable jacket  14  to allow relative freedom of movement between the optical fiber sub-units  12 , and the cable strength member  20  and/or the cable jacket  14 . As one non-limiting example, the inner diameter ID 1  of the cable jacket  14  may be 3.0 mm to 12.5 mm depending on the number optical fiber sub-units  12  included in the fiber optic cable  10 . As other non-limiting examples, as illustrated in  FIG. 2 , an outer diameter OD 2  of the optical fiber sub-unit  12  may be less than 3.1 millimeters (mm), and may be 3.0 mm, 2.0 mm, or 1.6 mm as examples. As another non-limiting example, the inner diameter ID 1  of the cable jacket  14  may be at least 0.5 mm greater than the collective outer diameter OD 1  of the optical fiber sub-units  12  and cable strength member  20 . 
     With reference back to  FIG. 1 , the optical fiber sub-units  12  may be disposed loosely inside the cable jacket  14  over the entire longitudinal length of the fiber optic cable  10 . Alternatively or in addition, the optical fiber sub-units  12  may be disposed at an end portion of the fiber optic cable  10 . If the optical fiber sub-units  12  are disposed loosely over the entire longitudinal length of the fiber optic cable  10 , this disposition may be accomplished during manufacturing of the fiber optic cable  10 . If the optical fiber sub-units  12  are disposed loosely at an end portion of the fiber optic cable  10 , this disposition may be accomplished post manufacturing of the fiber optic cable  10 . Examples of these techniques will be discussed in more detail below. 
     With continuing reference to  FIGS. 1 and 2 , the optical fiber sub-units  12  disposed in the fiber optic cable  10  also have the feature of constraining movement of the optical fibers  16  disposed therein. In this regard with reference to  FIG. 2 , the optical fibers  16  are disposed within the sub-unit jacket  18  of the optical fiber sub-unit  12 . One or more sub-unit strength members  22  are also disposed within the sub-unit jacket  18  adjacent the optical fibers  16 . The sub-unit strength members  22  may be manufactured from the same or different material than the cable strength member  20 . Also, the optical fibers  16  could be tight buffered within the sub-unit jackets  18  either adjacent to one or more sub-unit strength members  22  also provide within a sub-unit jacket  18  or in a sub-unit jacket  18  that does not include the sub-unit strength member  22 . 
     The quantity of strength members can be described by axial rigidity, which is the modulus of elasticity times the cross sectional area of a material. For a composite material such as a cable, the axial rigidity is the sum of the axial rigidity of the individual elements of the cable. For each component of a cable, the axial rigidity can be the load bearing area times the modulus of elasticity for the material. In this regard with reference to  FIG. 1 , the total axial rigidity of the fiber optic cable  10  may be the sum of the axial rigidity of the optical fiber sub-units  12 , the cable strength members  20 , the cable jacket  14 , and any other components of the fiber optic cable  10 . Likewise, the axial rigidity of each of the optical fiber sub-units  12  would be the sum of the axial rigidity of the sub-unit strength members  22 , the sub-unit jacket  18 , and any other components of the optical fiber sub-unit  12 . The total axial rigidity of the optical fiber sub-units  12  would be the sum of the axial rigidity of all the individual optical fiber sub-units  12 . In one embodiment, the strength of the optical fibers  16  is not included in the total axial rigidity of each of the optical fiber sub-units  12 , because the fiber optic cable  10  is designed to reduce the strain on the optical fibers  16 . In another embodiment, the strength of the optical fibers  16  can be included in the total axial rigidity of each of the optical fiber sub-units  12 . Further, the axial rigidity of the cable jacket  14  and the sub-unit jackets  18  as well as any fiber coatings on the optical fibers  16  may be insignificant enough to be ignored in an axial rigidity calculation. 
     As a non-limiting example, axial rigidity may be calculated as follows: 
               Axial_Rigidity   =       ∑   i     ⁢       E   i     ⁢     A   i           ,         
where:
         E i  is the elastic modulus of material i; and   A i  is the load bearing area of component i.       

     As an example, for a 380 grams denier (i.e., gram weight for 9000 meters) aramid yarn strength member, the sum of EA may be 3.33 kiloNewtons (kN). For a 1420 grams denier aramid yarn strength member, the EA may be 12.63 kN. In one embodiment, each optical fiber sub-units  12  may have four (4) 380 grams denier aramid yarns strength members  22 , providing for the total axial rigidity (i.e., ΣEA) of the sub-unit strength members  22  to be 4×3.33 kN=13.32 kN. The amount of cable strength member  20  provided in the fiber optic cable  10  located outside the sub-unit jackets  18  may vary based on the total optical fiber  16  count provided in the fiber optic cable  10 . The following table provides exemplary calculations for the axial rigidity of cable strength members  20  and the sub-unit strength members  22  of various possible fiber optic cable  10  designs in accordance with embodiments disclosed herein. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
               
               
                   
                   
                   
                 Number of 
                   
                   
                   
                   
               
               
                   
                   
                   
                 1420 
                   
                   
                   
                   
               
               
                   
                   
                   
                 grams 
                   
                   
                 % total 
                 % total 
               
               
                   
                 Number 
                 Sum of 
                 denier 
                 EA 
                   
                 EA in 
                 EA  
               
               
                   
                 of  
                 optical 
                 aramid 
                 outside 
                   
                 one 
                 in all 
               
               
                   
                 optical  
                 fiber  
                 yarns (200 
                 optical 
                   
                 optical 
                 optical 
               
               
                 Fiber 
                 fiber 
                 sub- 
                 outside 
                 fiber  
                   
                 fiber  
                 fiber  
               
               
                 optic 
                 sub- 
                 unit  
                 optical 
                 sub- 
                   
                 sub- 
                 sub- 
               
               
                 cable 
                 units  
                 (12) 
                 fiber sub- 
                 units  
                 Total  
                 unit  
                 units  
               
               
                 (10) 
                 (12) 
                 EA 
                 units (12) 
                 (12)  
                 EA 
                 (12) 
                 (12) 
               
               
                   
               
             
            
               
                  12 f 
                  1 
                  13.3 
                  8 
                 101.0 
                 114.4 
                 11.6% 
                 12% 
               
               
                  24 f 
                  2 
                  26.6 
                 12 
                 151.6 
                 178.2 
                  7.5% 
                 15% 
               
               
                  48 f 
                  4 
                  53.3 
                 12 
                 151.6 
                 204.8 
                  6.5% 
                 26% 
               
               
                  72 f 
                  6 
                  79.9 
                 16 
                 202.1 
                 282.0 
                  4.7% 
                 28% 
               
               
                  96 f 
                  8 
                 106.6 
                 16 
                 202.1 
                 308.6 
                  4.3% 
                 35% 
               
               
                 144 f 
                 12 
                 159.8 
                 16 
                 202.1 
                 361.9 
                  3.7% 
                 44% 
               
               
                   
               
            
           
         
       
     
     The same non-limiting examples provided above with regard to the cable strength member  20  are also applicable as non-limiting examples for the sub-unit strength members  22 . As additional non-limiting examples, the axial rigidity of each of the optical fiber sub-units  12  can be less than fifteen percent (15%) of the total axial rigidity of the one or more cable strength members  20  and the sub-unit strength members  22  of the fiber optic cable  10 . The combined axial rigidity of all of the sub-unit strength members  22  of the optical fiber sub-units  12  can be less than fifty percent (50%) of the total axial rigidity of the cable strength members  20  and the sub-unit strength members  22  of the fiber optic cable  10 . 
     With continuing reference to  FIG. 2 , the sub-unit strength members  22  are disposed longitudinally adjacent to the optical fibers  16  along the length of the optical fiber sub-units  12 . The optical fibers  16  are disposed inside the sub-unit jacket  18  such that movement of the optical fibers  16  is contained by an interior wall  24  of the sub-unit jacket  18  and/or the sub-unit strength members  22 . The optical fibers  16  may be constrained by friction themselves, which constrains the relative longitudinal movement of the optical fibers  16  relative to each other. For example, the group of optical fibers  16  inside each sub-unit jacket  18  may have an effective diameter of 1.0 mm inside a 1.4 mm inner diameter sub-unit jacket  18 . The sub-unit strength members  22  may be about 0.1 mm in thickness as an example. Thus, the optical fiber  16  to optical fiber  16  contact is provided by the limited free space within the optical fiber sub-unit  12  that enables the friction between the optical fibers  16  to limit relative longitudinal movement between the optical fibers  16 . The ability to produce low skew optical fiber sub-units  12  can be determined in the ability to limit the relative longitudinal movement of the individual optical fibers  16  within an optical fiber sub-unit  12 . 
     Constraining the optical fibers  16  within the optical fiber sub-units  12  may allow the optical fibers  16  disposed within a given optical fiber sub-unit  12  to be held together as a unit within the optical fiber sub-unit  12 . As will be discussed in more detail below, by providing the optical fibers constrained as a unit in optical fiber sub-units, the optical fiber sub-units may be exposed and constrained in a furcation assembly without exposing the optical fibers contained in the optical fiber sub-units. This feature may reduce complexity and labor costs in furcation assembly preparations. Further, the optical fibers may be subjected to less risk of damage if not exposed in a furcation assembly. 
     Constraining the optical fibers  16  within the optical fiber sub-units  12  may also provide low optical skew of the fiber optic cable  10  acting as a parallel optic system with multiple optical fibers  16  disposed in each optical fiber sub-unit  12 . As non-limiting examples, constraining the optical fibers  16  in the optical fiber sub-units  12  may provide an optical skew less than 6.1 picoseconds (ps) per meter (m) (ps/m). As another non-limiting example, constraining the optical fibers  16  in the optical fiber sub-units  12  may provide an optical skew less than 3.6 ps/m. As non-limiting examples, constraining the optical fibers  16  in the optical fiber sub-units  12  may also allow the optical fibers  16  within each optical fiber sub-unit  12  to act as anti-buckling components within the fiber optic cable  10  to resist bending and avoid optical attenuation that would result from such bending. 
     The fiber optic cable  10  in  FIG. 1  can be furcated to expose the optical fiber sub-units as furcation legs for connecting the optical fibers to other connectors, adapters, or fiber optic equipment. In this regard,  FIG. 3  illustrates a top perspective view of an exemplary fiber optic cable assembly  26  that includes the fiber optic cable  10  in  FIG. 1 . As illustrated in  FIG. 3 , the fiber optic cable assembly  26  includes a furcation assembly  28 . In this embodiment, the furcation assembly  28  is a furcation plug  30 , but the furcation assembly  28  may be comprised of alternative furcation assemblies as will be discussed in more detail below. End portions  32  of the optical fiber sub-units  12  extend from the furcation plug  30  to provide furcated legs. The optical fiber sub-units  12  can provide furcated legs without the need for additional furcation tubing. The optical fiber sub-units  12  in this embodiment do not have preferential bend. As a non-limiting example, this may allow the optical fiber sub-units  12  acting as furcated legs to be about 2.0 mm to 3.0 mm in outer diameter, which may reduce congestion of furcated legs in fiber optic equipment. The end portions  32  of the optical fiber sub-units  12  are connectorized with fiber optic connectors  34  to provide connection access to the optical fibers  16  contained in the optical fiber sub-units  12 . For example, the fiber optic connectors may be multi-fiber termination push-on (MTP) style fiber optic connectors, but other fiber optic connector types are also possible, including but not limited to SC, FC, LC, ST, and duplex connectors. 
     As will be discussed in more detail below, providing the optical fibers  16  constrained in the optical fiber sub-units  12  while providing for movement of the optical fiber sub-units  12  within the cable jacket  14  relative to the cable jacket  14  and/or the cable strength member  20  can provide certain non-limiting advantages. One advantage includes the furcation assembly  28  directing tensile load (e.g., a pulling load) away from the optical fibers  16  and to the cable jacket  14  and/or the cable strength member  20 . Another advantage includes not having to expose the optical fibers  16  from within the sub-unit jacket  18  in the furcation assembly  28  to secure the optical fibers  16  therein. Because the optical fibers  16  are constrained within the sub-unit jacket  18 , constraining of the sub-unit jackets  18  can provide sufficient securing of the optical fibers  16  in the furcation assembly  28 . The process of exposing optical fibers  16  within a sub-unit jacket  18  can be more costly in terms of time and labor costs than the ability to secure the sub-unit jackets  18  in the furcation assembly  28  without having to expose the optical fibers  16 . 
     Prior to providing the furcation assembly  28  in  FIG. 3 , the fiber optic cable  10  undergoes certain preparations. In this regard,  FIG. 4  is provided.  FIG. 4  illustrates an end portion  36  of the fiber optic cable  10  in  FIG. 1 . The end portion  36  of the fiber optic cable  10  is cut to a desired length. Thereafter, a portion of the cable jacket  14  is windowed or removed to expose end portions  32  of the optical fiber sub-units  12  and an end portion  38  of the cable strength member  20 . As a result, a transition interface  42  is provided between an end  44  of the cable jacket  14  and the optical fiber sub-units  12  and cable strength member  20 . The end portion  38  of the cable strength member  20  may be optionally twisted, as illustrated in  FIG. 4 , prior to preparing a furcation assembly in the end portion  36  of the fiber optic cable  10  to enhance the strength of the cable strength member  20  when disposed in a furcation assembly. To retain the twist in the end portion  38  of the cable strength member  20 , tape  48  or other securing means may be disposed around an end  46  of the cable strength member  20 . 
       FIG. 5  is a side view of a cross-section of the fiber optic cable assembly  26  in  FIG. 3  illustrating the optical fiber sub-units  12  and cable strength member  20  disposed in the furcation plug  30  to provide the furcation assembly  28 . The end portions  32  of the optical fiber sub-units  12  are disposed through a first end  50  of the furcation plug  30 , into an interior chamber  51  of the furcation plug  30 , and extend out from a second end  52  of the furcation plug  30 . Note that optical fibers  16  are not exposed from the optical fiber sub-units  12  in the interior chamber  51  of the furcation plug  30 , because the optical fibers  16  are constrained in the sub-unit jackets  18 . The end portion  38  of the cable strength member  20  is also disposed through the first end  50  of the furcation plug  30 . 
     With continuing reference to  FIG. 5 , the cable strength member  20  is cut so that an end  54  of the cable strength member  20  does not extend through the second end  52  of the furcation plug. The end  54  of the cable strength member  20  is retained inside the interior chamber  51  of the furcation plug  30 . The end  44  of the cable jacket  14  is terminated inside the interior chamber  51  of the furcation plug  30 . A potting compound or epoxy  56  can be disposed in the interior chamber  51  of the furcation plug  30  to secure the portion of end portion  38  of the cable strength member  20  and portions of the end portion  32  of the optical fiber sub-units  12  in the furcation plug  30 . In this manner, when a tensile or tensile load (e.g., a pulling load) P 1  is placed on the furcation plug  30 , the tensile load P 1  can be translated to the cable strength member  20  and/or cable jacket  14  secured inside the interior chamber  51  of the furcation plug  30 . 
       FIG. 6  illustrates the fiber optic cable assembly  26  of  FIG. 5 , but an optional strain relief device  60  and cable wrap  62  are provided. The strain relief device  60  interfaces between the cable jacket  14  and the first end  50  of the furcation plug  30  to provide strain relief when the cable jacket  14  is bent about the furcation plug  30 . The strain relief device  60  may be a boot, and may be a separate or integral component to the furcation plug  30 . The cable wrap  62  may be disposed around the optical fiber sub-unit  12  to group the optical fiber sub-units  12  together extending from the second end  52  of the furcation plug  30 . An end  64  of the cable wrap  62  may be secured inside the furcating plug  30 . 
     To further improve the pulling characteristics of the furcation assembly  28  in  FIGS. 5 and 6  to direct tensile load (e.g., a pulling load) away from the optical fibers  16 , the features of the fiber optic cable  10  can be employed. Specifically, the end portion  38  of the cable strength member  20  can be pulled taut prior to securing the end portion  38  in the furcation plug  30 , as illustrated in  FIG. 5 . Because the optical fiber sub-units  12  can be loosely disposed in the cable jacket  14  of the fiber optic cable  10 , the length of the optical fiber sub-units  12  with the cable jacket  14  can be made longer than the length of the cable strength member  20 . The length of the cable strength member  20  is greater than the length of the optical fiber sub-units  12  in the cross-section of the cable jacket  14  adjacent to the transition interface  42  in this embodiment. The length of the cable strength member  20  can also be greater than the length of the optical fiber sub-units  12  in the cross-section of the cable jacket  14  in any portion of the fiber optic cable  10  if the optical fiber sub-units  12  are provided longer than the cable strength member  20  over the entire length of the fiber optic cable  10  during manufacturing of the fiber optic cable  10 . 
     As one non-limiting example, the relative longitudinal movement of the optical fiber sub-units  12  within the end  44  of the cable jacket  14  can be greater than four (4) mm. In another non-limiting example, the relative longitudinal movement of the optical fiber sub-units  12  within the end  44  of the cable jacket  14  can be greater than ten (10) mm. In this regard, when the tensile load (e.g., a pulling load) P 1  is placed on the furcation plug  30 , the tensile load P 1  is directed primarily to the taut cable strength member  20  as opposed to primarily the optical fiber sub-units  12  and optical fibers  16  disposed therein. The cable strength member  20  will carry the bulk of the tensile load P 1  while directing less of the tensile load P 1  to the optical fiber sub-units  12 . The tensile load P 1  may be directed away from the optical fiber sub-units  12  and optical fibers  16  disposed therein. In this manner, damage to the optical fibers  16  is reduced or eliminated as a result of pulling the fiber optic cable  10 . 
     Providing the cable strength member  20  in the cable jacket  14  of the fiber optic cable  10  of a length shorter than the optical fiber sub-units  12  can be accomplished in at least two methods. In one method, end portions  32  of the optical fiber sub-units  12  can be pushed into the end  44  of the cable jacket  14 , as illustrated in  FIGS. 5 and 6 . The end portion  38  of the cable strength member  20  is pulled taut from the end  44  of the cable jacket  14  so that the length of the cable strength member  20  is shorter than the length of the optical fiber sub-units  12 . 
     The length of the optical fiber sub-units  12  can also be provided longer within the cable jacket  14  than the cable strength member  20  during manufacture of the fiber optic cable  10 . The tension at which the optical fiber sub-units  12  may be fed may be lower than the tension in which the cable strength member  20  may be fed during manufacture of the fiber optic cable  10  resulting in longer length optical fiber sub-units  12 . For example, the length of the cable strength member  20  disposed in the cable jacket  14  may be shorter than the length of the optical fiber sub-units  12  by 1.0 mm to 6.0 mm per meter (mm/m) length of the cable jacket  14  or more. As another example, the length of the cable strength member  20  disposed in the cable jacket  14  may be shorter than the length of the optical fiber sub-units  12  up to 1 percent (1%), or 0.5 percent (0.5%), or even 0.1 percent (0.1%). In this regard,  FIG. 7  is a top perspective view of the fiber optic cable assembly  26  in  FIG. 5 , wherein the furcation plug  30  is arranged to be enclosed with an exemplary pulling grip sub-assembly  66  comprised of two shells  68 A,  68 B adapted to be disposed on each other to secure the furcation plug  30  therebetween for pulling the fiber optic cable  10 .  FIG. 8  illustrates the fiber optic cable assembly  26  in  FIG. 7  with the furcation plug  30  enclosed in the pulling grip sub-assembly  66  and enclosed in an exemplary pulling bag  70  for pulling the fiber optic cable  10 . A loop  72  is disposed on an end  74  of the pulling bag  70  opposite of an end  76  retaining the pulling grip sub-assembly  66  for pulling the fiber optic cable  10 .  FIG. 9  is a top perspective view of a fiber optic cable assembly that is similar to the fiber optic cable assembly  26  of  FIG. 3 , but employing an alternative exemplary furcation plug  80 . A pulling grip sub-assembly can be designed to retain the furcation plug  80 , which can be disposed in the pulling bag  70  in  FIG. 8  to pull the fiber optic cable. 
     In one embodiment, the furcation plug  30  does not transfer the tensile load P 1  placed on the furcation plug  30  to the optical fiber sub-units  12 . In another embodiment, the furcation plug  30  is configured to sustain a tensile load of at least 100 pounds (lbs.) while producing less than 0.3% strain on the optical fiber sub-unit  12 . In another embodiment, the furcation plug  30  is configured to sustain a tensile load of at least 150 lbs. while producing less than 0.2% strain on the optical fiber sub-units  12 . 
     Other furcation assemblies can be provided that employ the fiber optic cable  10  in  FIG. 1  or a fiber optic cable that contains some or all features provided in the fiber optic cable  10  in  FIG. 1 . In this regard,  FIG. 10A  illustrates an alternative fiber optic cable assembly  90 . The fiber optic cable assembly  90  includes a furcation assembly  92  that furcates the optical fiber sub-units  12  and provides a cable strength member pulling loop  94 , as opposed to a furcation plug, for pulling the fiber optic cable  10 .  FIG. 10B  illustrates the fiber optic cable assembly  90  in  FIG. 10A  with the cable strength member pulling loop  94  fully assembled. As illustrated in  FIG. 10A , the cable strength member pulling loop  94  is formed by looping a first end  97  of a cable strength member end portion  96  back onto itself and towards a cable jacket tube  98  of the fiber optic cable  10 . In this manner, the cable strength member pulling loop  94  can be pulled to pull the fiber optic cable  10 , wherein the tensile load (e.g., a pulling load) is directed onto the cable strength member pulling loop  94 , which is formed from the cable strength member  20  disposed inside the fiber optic cable  10 . Any size of cable strength member pulling loop  94  may be formed as desired. Because the cable strength member pulling loop  94  transfers tensile load directly to the cable strength member  20 , the cable strength member pulling loop  94  does not transfer the tensile load to the optical fiber sub-units  12 . 
     As one non-limiting example, the cable strength member pulling loop  94  may be two (2) to three (3) inches in circumference. The first end  97  of the cable strength member end portion  96  is secured to the cable jacket  14  to secure the formation of the cable strength member pulling loop  94  in this embodiment.  FIG. 10B  illustrates the cable jacket tube  98  after being heat shrunk onto the cable strength member pulling loop  94  and the cable jacket  14  of the fiber optic cable  10  to secure the cable strength member pulling loop  94  to the cable jacket  14 . As one non-limiting example, the cable jacket tube  98  may be heated to a temperature between 100 and 200 degrees Celsius for between two (2) and four (4) minutes to heat shrink and secure the cable jacket tube  98  to the cable strength member end portion  96  and the cable jacket  14 . The cable strength member pulling loop  94  may further be disposed with a heat shrink tube  100 , as illustrated in  FIG. 10B , or may only consist of the cable strength member  20  without additional tubing, as illustrated in  FIG. 11 . 
       FIGS. 12-15  illustrate another exemplary fiber optic cable assembly  102  that may include a furcation assembly  101  disposed in a fiber optic cable  10 , including the fiber optic cable  10  in  FIG. 1 . In this embodiment, a cable strength member pulling loop  103  is formed by the cable strength member end portion  96  disposed in two strength member tubes  104 A,  104 B to form an additional neck portion  106  in the cable strength member pulling loop  103 . Providing a neck portion  106  in the cable strength member pulling loop  103  may assist in translating a tensile load (e.g., a pulling load) applied to the cable strength member pulling loop  103  in alignment with the longitudinal axis of the cable strength member  20  disposed inside the fiber optic cable  10 . This may allow a greater tensile load to be applied to the cable strength member end portion  96 . Because the cable strength member pulling loop  103  transfers tensile load directly to the cable strength member  20 , the cable strength member pulling loop  103  does not transfer tensile load to the optical fiber sub-units  12 . 
     The strength member tubes  104 A,  104 B may be heat shrink tubes. In this regard, heat can be applied to the strength member tubes  104 A,  104 B to heat shrink the strength member tubes  104 A,  104 B to be secured in place onto the cable strength member end portion  96  to form the neck portion  106  and a loop portion  108  in the cable strength member pulling loop  103 , as illustrated in  FIGS. 12 and 13 . A tensile load placed on the loop portion  108  is translated to the neck portion  106 , which is disposed along a longitudinal axis A 1  as illustrated in  FIG. 13 . Thus, if the neck portion  106  is disposed along a longitudinal axis A 2  of the fiber optic cable  10 , the tensile load will be directed to the cable strength member  20  without the cable strength member  20  applying a force onto or expanding the cable jacket  14 . As one non-limiting example, the strength member tubes  104 A,  104 B in  FIG. 13  may be heated to a temperature between 100 and 200 degrees Celsius for between two (2) and four (4) minutes to heat shrink and secure the strength member tubes  104 A,  104 B to the cable strength member end portion  96  to form the cable strength member pulling loop  103 . As also illustrated in  FIG. 13 , a first end  110  of the cable strength member end portion  96  can be pulled back onto and fanned about the cable jacket  14  of the fiber optic cable  10  to distribute the first end  110  onto the cable jacket  14 . The first end  110  of the cable strength member end portion  96  can be secured to the cable jacket  14 , such as with tape  112  or other securing means, as illustrated in  FIG. 13 . 
     With reference to  FIG. 14 , to secure the first end  110  of the cable strength member end portion  96 , a cable jacket tube  114  is provided as illustrated in  FIGS. 14 and 25 . The cable jacket tube  114  is used to secure the cable strength member pulling loop  103  to the cable jacket  14  of the fiber optic cable  10 .  FIG. 14  illustrates the cable jacket tube  114  before being heat shrunk onto the first end  110  of the cable strength member end portion  96  and the cable jacket  14  of the fiber optic cable  10 .  FIG. 15  illustrates the cable jacket tube  114  after being heat shrunk onto the first end  110  and the cable jacket  14  of the fiber optic cable  10 . With reference to  FIG. 14 , the cable jacket tube  114  is disposed over the first end  110  of the cable strength member end portion  96  and the cable jacket  14  of the fiber optic cable  10  before the cable strength member pulling loop  103  is secured. 
     For example, the cable jacket tube  114  may be a heat shrink tube. In this regard, the cable jacket tube  114  is heated to heat shrink the cable jacket tube  114  onto the first end  110  of the cable strength member end portion  96  and the cable jacket  14  to secure the formed cable strength member pulling loop  103 , as illustrated in  FIG. 15 . As one non-limiting example, the cable strength member pulling loop  103  may be heated to a temperature between 100 and 200 degrees Celsius for between two (2) and four (4) minutes to heat shrink and secure the cable jacket tube  114  to the cable strength member end portion  96  and the cable jacket  14 . A pressing force may be applied to the cable jacket tube  114  to promote adhesion between the cable jacket tube  114  and the cable strength member end portion  96  to secure the cable strength member pulling loop  103  to the cable jacket  14  of the fiber optic cable  10 . 
     As used herein, it is intended that terms “fiber optic cables” and/or “optical fibers” include all types of single mode and multi-mode light waveguides, including one or more optical fibers that may be up-coated, colored, buffered, ribbonized and/or have other organizing or protective structure in a cable such as one or more tubes, strength members, jackets or the like. The optical fibers disclosed herein can be single mode or multi-mode optical fibers. Likewise, other types of suitable optical fibers include bend-insensitive optical fibers, or any other expedient of a medium for transmitting light signals. An example of a bend-insensitive, or bend resistant, optical fiber is ClearCurve® Multimode fiber commercially available from Corning Incorporated. Suitable fibers of this type are disclosed, for example, in U.S. Patent Application Publication Nos. 2008/0166094 and 2009/0169163. 
     Many modifications and other embodiments of the embodiments set forth herein will come to mind to one skilled in the art to which the embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. As non-limiting examples, the number of optical fiber sub-units, the number of optical fibers provided within each optical fiber sub-unit, and the number of cable strength members provided in the fiber optic cable can vary as desired. The number of sub-unit strength members provided in each sub-unit jacket of an optical fiber sub-unit can vary as desired. The optical fibers can be buffered or non-buffered. The optical fibers can be tight buffered, such as within an optical fiber sub-unit cable either adjacent to one or more strength members in a sub-unit jacket or in a sub-unit jacket that does not include any strength members. Any type of furcation assembly desired can be employed to provide a furcation of the optical fiber sub-units from the fiber optic cable. The dimensions of any of the components disclosed herein can vary or be set as desired. 
     Therefore, it is to be understood that the description and claims are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. It is intended that the embodiments cover the modifications and variations of the embodiments provided they come within the scope of the appended claims and their equivalents. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.