Abstract:
A fiber optic cable with first and second cavities accommodating separate groups of fibers. Arranging the optical fibers in separate cavities allows the fibers to be distinguished from one another without requiring secondary marking indicia such as stripes on the fibers. The cable jacket can be extruded such that the cavities are formed integrally in the jacket during extrusion.

Description:
BACKGROUND 
     The present disclosure relates to fiber optic cables and more specifically to fiber optic cables having a structure that segregates groups of optical fibers within the cable. 
     In a fiber optic network, numerous connections between fiber optic cables are required. The present standard in the art utilizes male and female industry-standard MTP connectors, which employ precision guide pins to align the internal fibers of the fiber optic cable, when connecting fiber optic cables. An MTP connector typically connects a multi-fiber cable having twelve optical fibers. 
     Individual fibers in a multi-fiber cable are often distinguished from one another by color-coded jackets or buffers and an identification scheme has been developed to allow for rapid identification of the optical fibers. This is important because connecting an MTP connector correctly to a multi-fiber cable requires precise knowledge of the connection scheme of the optical fibers in the cable. The current color identification scheme includes 12 distinct colors that are used to identify the fibers. 
     With the amount of data to be transmitted increasing, data centers are now using fiber optic cables containing, for example, 24 optical fibers and 24 fiber MTP optical connectivity hardware to connect the 24 fiber cable to various devices. The 24 fiber cable improves efficiency as well as data transmission density and bandwidth. For cables having more than twelve fibers, the standard 12 color code must repeat itself. Thus, in the case of a 24 fiber cable, there are two optical fibers identified with each of the colors. The two groups can be distinguished by adding, for example, a stripe or some other identifying indicia to one set of fibers. Applying a dash or stripe to the fibers, however, requires operating at a low line speed, rendering the manufacturing process less efficient. 
     Alternatively, fiber groups can be distinguished by bundling one of the fiber groups, such as by wrapping the group in a binder thread. However, the thread binder can untwist while removing the cable jacket so that the installer can no longer distinguish between the fiber groups. 
     SUMMARY 
     In one embodiment, a fiber optic cable comprises an elongated jacket of continuous cross-section, a first cavity in the jacket and extending therealong, a first group of optical fibers located within the first cavity, a second cavity in the jacket and extending therealong, a second group of optical fibers located within the second cavity, and at least one strength member within and extending along the jacket, wherein the jacket is extruded such that the first and second cavities are formed during extrusion of the jacket. Providing separate cavities for the respective groups of fibers distinguishes the groups from each other, for example, during installation of a connector on an end of the cable. Extruding the cable jacket as a unitary piece is an efficient way to segregate the first and second fiber groups in their respective cavities. Each group of fibers can include twelve fibers, with each fiber in the first group having a corresponding fiber in the second group of identical color and appearance, without the requirement of additional identifying indicia. 
     According to another embodiment, a fiber optic cable comprises a jacket, a cavity within the jacket extending therealong, an insert within and extending along the cavity, the insert comprising a central partition and a pair of end portions connected to the central partition, the central partition dividing the cavity into a first region and a second region, a first plurality of optical fibers grouped together in a first group in the first region, a second plurality of optical fibers grouped together in a second group in the second region, and at least one strength member within and extending along the jacket. The insert separates the respective groups of fibers to that they can be distinguished, for example, during installation of a connector on an end of the fiber optic cable. 
     According to yet another embodiment, a malleable tape can be used to form first and second regions within a fiber optic cable. 
     According to the present embodiments, a trunk or breakout cable can be formed using a plurality of any of the cables disclosed in this specification. The individual cables can be wrapped or stranded around a strength member, and enclosed within an outer jacket. 
     It is to be understood that both the foregoing summary and the following detailed description are merely exemplary of preferred embodiments, and are intended to provide an overview or framework to understanding the nature and character of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components of the following figures are illustrated to emphasize the general principles of the present disclosure and are not necessarily drawn to scale. Reference characters designating corresponding components are repeated as necessary throughout the figures for the sake of consistency and clarity. 
         FIG. 1  is schematic cross-sectional view of a fiber optic cable according to a first embodiment. 
         FIG. 2  is schematic cross-sectional view of a fiber optic cable according to a second embodiment. 
         FIG. 3  is schematic cross-sectional view of a fiber optic cable according to a third embodiment. 
         FIG. 4  is schematic cross-sectional view of a fiber optic cable according to a fourth embodiment. 
         FIG. 5  is schematic cross-sectional view of a fiber optic cable according to a fifth embodiment. 
         FIG. 6  is schematic cross-sectional view of a fiber optic cable according to a sixth embodiment. 
         FIG. 7  is schematic cross-sectional view of a fiber optic cable according to a seventh embodiment. 
         FIG. 8  is schematic cross-sectional view of a fiber optic cable according to an eighth embodiment. 
         FIG. 9  is schematic cross-sectional view of a fiber optic cable according to an ninth embodiment. 
         FIG. 10  is schematic cross-sectional view of a fiber optic cable according to a tenth embodiment. 
         FIG. 11  is schematic cross-sectional view of a fiber optic trunk cable. 
     
    
    
     DETAILED DESCRIPTION 
     The fiber optic cable constructions disclosed herein segregate at least two optical fiber groups, wherein each group contains a plurality of optical fibers. The plurality of optical fibers may number twelve. Generally, the cable constructions disclosed herein as exemplary embodiments comprise two segregated groups of twelve optical fibers of the same color and appearance. The cross-sections in this specification are taken on a plane perpendicular to the length of the cables. 
       FIG. 1  is a schematic cross-sectional view of a fiber optic cable  10  according a first embodiment. The fiber optic cable  10  has an elongated jacket  12  that surrounds a first cavity or first lumen  16  and a second cavity or second lumen  18  with both cavities extending along the length of the jacket  12 . A first plurality  20  of optical fibers  21  form a first group  20  that extends along the length of the first cavity  16 . A second plurality  22  of optical fibers  23  forms a second group  22  that extends along the length of the second cavity  18 . The first plurality  20  of optical fibers  21  may be bundled together and the second plurality  22  of optical fibers  23  may be bundled together. The first plurality  20  of optical fibers  21  and the second plurality  22  of optical fibers  23  are separated from each other by a structure or barrier, which in this case is a portion of the jacket  12  extending between the cavities  16 ,  18 . The cable  10  can also include one or more strength members  24  which may be arranged in one or both of the first cavity  16  and the second cavity  18  and extends the length of the respective cavities. 
     The cable  10  has a generally circular cross section  14 . The cross-section  14  may have a diameter less than or equal to about 4.0 mm, or less than or equal to 3.3 mm. The first cavity  16  and the second cavity  18  also have circular cross-sections  17 ,  19 , respectively. It is not required, however, that they be circular in cross-section or that they have the same cross-sectional shape. The cross-sectional area of the first cavity  16  and the second cavity  18  each may be at least 1.10 millimeters squared (mm 2 ) and in some embodiments each cross-sectional area may be at least 1.25 mm 2 . A cavity cross-sectional area of 1.25 mm 2  provides a packing density of about 70% when twelve optical fibers are accommodated in each cavity. If for example, eight fibers are provided in each cavity, the cavities may each have a cross-sectional area of at least 0.85 mm 2 . Generally, the strength members  24  may be arranged toward the center of the cable  10  and each cavity  16 ,  18  can include one, two, or more strength members  24 . 
       FIGS. 2 and 3  are schematic cross-sectional views of fiber optic cable  30 ,  50  according to second and third embodiments, respectively. The cables  30 ,  50  have respective generally circular cross-sections  34 ,  54 . The cross-sections  34 ,  54  may have a diameter of less than or equal to about 3.3 mm. The first cavities  36 ,  56  and the second cavities  38 ,  58  each have non-circular cross-sections  37 ,  39 , and  57 ,  59  respectively. The cross-sectional area of the first cavity  36 ,  56  and the second cavity  38 ,  58  each may be at least 1.10 mm 2  and in some embodiments may be at least 1.25 mm 2 . Generally, for the cable  30 , the strength members  44  may be arranged toward the center of the cable  30  and each cavity  36 ,  38  can have one or more strength members  44 . Four strength members  64  are shown in the exemplary cable  50  with the strength members  64  arranged at the peripheries of the cavities  56 ,  58 . 
       FIG. 4  is a schematic cross-sectional view of the fiber optic cable  90  of non-circular cross-section  94 . The cross-section  94  may be elliptical or oval in shape, and may have an area less than about 10 mm 2 . An oval or elliptical cross-section  94  may maintain cable  90  robustness while also minimizing the size and cost of the cable  90 . The oval or elliptical cross-section  94  can be designed to provide the cable  90  with a preferential bend direction. Furthermore, the cross-section  94  may provide improved mechanical performance with regards to crush and impact since the cable  90  may be oriented in the preferential bend direction when being crushed. A crush load applied in the vertical direction in  FIG. 4 , for example, may be borne along the central portion of the cable, while the optical fibers are generally disposed to the sides of the cable. The aspect ratio of the elliptical cross-section  94  may range from about 1:1 to about 3.6:2.6, where aspect ratio is a ratio of the measure of a major or largest axis of the ellipse to a minor or smallest axis of the ellipse. An ovality for the cross-section  94  may be at least 0.8, where ovality is a ratio of the minor axis of the oval to the major axis of the oval. While the terms “ellipse” and “oval” are used to describe various embodiments of this specification, the cross-sectional shapes need not necessarily follow these precise geometrical constructs, but instead may simply approximate the shape or appearance of a true “ellipse” or “oval.” 
     The exemplary first cavity  96  and the second cavity  98  have generally circular cross-sections  97 ,  99 , respectively. The cross-sectional area of the first cavity  96  and the second cavity  98  each may be at least 1.10 mm 2  and in some embodiments at least 1.25 mm 2 . Each cavity  96 ,  98  can include one or more strength members  104  that can be oriented toward the inner portion of the cavities. The fiber optic cable  90  can include one or more optional access features  106  formed in and extending along the periphery of the jacket  92 . The access features  106  are configured to facilitate opening selected portions of the jacket  92  to allow access to one or both of the fiber groups  100 ,  102 . The access features  106  in the illustrated embodiment have the form of a partial slit or notch  107  that extends along the length of the jacket  92 . As shown in  FIG. 4 , a pair of slits  106  can be arranged at each end of the cable  90  so that a section of the jacket  92  between the slits can be removed, allowing access to the fiber groups in either of the cavities  96 ,  98 . The slits  106  extend a inwardly from the jacket  92  exterior. 
       FIG. 5  is a schematic cross-sectional views of a fiber optic cable  110 . The cable  110  is substantially identical to the cable illustrated in  FIG. 1 , except that the cable jacket  112  includes strength members  118  extending longitudinally through cavities  119  in the cable jacket. As illustrated in  FIG. 5 , the strength members  118  are aramid yarns arranged loosely in the cavities  119 .  FIG. 6  illustrates an alternative embodiment of a cable  120  substantially identical to that of  FIG. 5 , where the cable jacket  122  includes strength members  128  embedded within cavities  129 . In  FIG. 6 , the cable jacket  112  is extruded around the strength members  128  so that that the aramid yarns adhere to the polymer of the jacket  112 . Strength members  118 ,  128  as shown in  FIGS. 5 and 6  can be incorporated into the jackets of any of the embodiments shown in  FIGS. 1-4 . 
     According to the embodiments disclosed in  FIGS. 1-6 , the first and second cavities are defined by cable jackets that are a single, continuous (or, not formed from separate pieces or materials), uniform, polymer element extruded in a one-pass process. It is to be understood, however, that coextrusion methods may allow the use of different polymer materials to form a continuous polymer jacket in a one-pass process. The first cavities can have the same or similar cross-sectional shapes as the second cavities, and can be arranged on each side of the cable jackets so that the cables are symmetric about a central plane. In the oval or elliptical embodiments of  FIGS. 4 and 5 , the central plane can be defined along the minor axis of the ellipse. In the illustrated embodiments, the central plane is a plane of symmetry dividing the cables in half and passing through the barrier between the cavities (corresponding to vertical bisection lines in the figures), so that the cavities lie on opposite sides of the central plane. The individual fibers in the first groups can contact the portion of the jacket defining the first cavities, and the fibers in the second groups can contact the portion of the jacket defining the second cavities. 
       FIGS. 7 and 8  are schematic cross-sectional views of fiber optic cables  150 ,  170  according to embodiments seven and eight. The cables  150 ,  170  are of similar construction with common features, and thus will be discussed collectively. The fiber optic cable  150 ,  170  has a jacket  151 ,  171  that surrounds a cavity  152 ,  172 , extending along the length of the jacket  151 ,  171 . A first plurality  154 ,  174  of optical fibers  155 ,  175  form a first group  154 ,  174  that extends along the length of the cavity  152 ,  172 . A second plurality  156 ,  176  of optical fibers  157 ,  177  forms a second group  156 ,  176  that extends along the length of the cavity  152 ,  172 . The first groups and the second groups can be optionally bundled. The first fiber group  154 ,  174  and the second fiber group  156 ,  176  are separated from each other by a structure or barrier  158 ,  178 . The cable  150 ,  170  can include one or more strength members  160 ,  180 , which may be arranged in the cavity  152 ,  172  and extending the length of the cavity. 
     Referring specifically to  FIG. 7 , the barrier  158  divides the cavity  152  into two regions  162 ,  164  and physically separates the first fiber group  154  from the second fiber group  156 . The barrier  158  can be an insert, such as a plastic piece into which fibers are inserted before the jacket  151  is extruded thereover. The insert  158  has a central partition  166  and two curved end portions  168  extending from opposite ends of the partition  166 . The curved end portions  168  can be arcuate and can conform to an inner periphery of the jacket  151  over an arcuate distance. Gaps  169  are present between adjacent ends of the end portions  168 . During manufacture, the gaps  169  between the end portions  168  can be widened to allow insertion of optical fibers into the insert  158 . Each end portion  168  can conform to at least 50 degrees of arc of the inside of the jacket  151 . 
     Referring specifically to  FIG. 8 , the barrier  178  separates the first group  174  from the second group  176  and divides the cavity  172  into two regions  182 ,  186 . The barrier  178  can be an insert, such as a plastic piece into which fibers are inserted before the jacket  171  is extruded thereover. The insert  178  has a central partition  179  and two curved end portions  187  extending from opposite ends of the partition  179 . The curved end portions  187  can be arcuate and can conform to an inner periphery of the jacket  171  over a distance at least 50 degrees of arc. Gaps  189  allow insertion of optical fibers during manufacture. 
       FIG. 9  is a schematic cross-sectional view of a fiber optic cable  190  having an elongated jacket  191  that surrounds a cavity  192 . A first plurality  194  of optical fibers  195  form a first fiber group  194  that extends along the length of the cavity  192 . A second plurality  196  of optical fibers  197  forms a second fiber group  196  that extends along the length of the cavity  192 . A structure or barrier  198  partitions the cavity into two regions  202 ,  204  and physically separates the first group of fibers  194  from the second group of fibers  196 . The cable  190  can include one or more strength members  200  arranged in the cavity  192  and extending the length of the cavity. The exemplary barrier  198  is a plastic insert that bisects the cavity  192  so that a central plane of the cable  190  bisects the insert. The barrier  198  has opposed, inwardly curved concave walls  206  that face the groups of optical fibers  194 ,  196 . 
       FIG. 10  is a schematic cross-sectional view of a fiber optic cable  210  having an elongated jacket  211  that surrounds a cavity  212  extending along the length of the jacket  211 . A first plurality  214  of optical fibers  215  form a first group  214  and a second plurality  216  of optical fibers  217  forms a second group  216  that extends along the length of the cavity  212 . One or both groups  214 ,  216  can be bundled. A barrier  218  partitions the cavity into two regions  212 ,  214  and physically separates the first group of fibers  214  from the second group of fibers  216 . The cable  210  can include on or more strength members  220  extending the length of the cavity. In  FIG. 10 , the barrier  218  has the form or a malleable tape dividing the cavity  212  into the two regions  212 ,  214 . During manufacture, the tape  218  can be open to allow insertion of optical fibers, and then substantially closed to allow extrusion of the jacket  211  around the tape  218 . Opposites sides  228 ,  229  of the tape  218  can be tinted different colors to identify the fibers in each region  212 ,  214 . The malleable tape  218  can be a plastic material capable of deformation within the cable jacket  211 . Malleable materials such as, for example, polytetrafluoroethylene (PTFE), and commercially available materials such as Teflon®, can be used to form the tape  218 . 
     In the embodiments described in this specification, a matrix material having a consistency of, for example rubber cement, may be used to bundle each of the first groups and/or the second groups of optical fibers. The matrix material may be an ultra-violet curable matrix material. To distinguish between the two groups of optical fibers, a colored or tinted matrix material may be used for one, or both of the groups. 
       FIG. 11  is a schematic cross-sectional view of a fiber optic trunk or breakout cable  260  having a polymer jacket  262  surrounding six cables  90  as shown in  FIG. 4 . The trunk cable  260  may, however, comprise a plurality of any of the fiber optic cables  10 ,  30 ,  50 ,  110 ,  120 ,  150 ,  170 ,  190 ,  210 . The trunk cable  260  also has a central strength member  264 , around which a plurality of cables may be stranded or otherwise arranged on the periphery of the strength member  264 . The illustrated central member  264  is a coated glass-reinforced plastic (GRP). The trunk cable  260  can also include additional strength members  266  for added tensile strength. 
     According to the embodiments disclosed in this specification, during cable access and connectorization of 24f cables, for example, the installer can easily distinguish between fibers  1 - 12  in the first fiber group of fibers from fibers  13 - 24  in the second fiber group, without requiring additional marking indicia for the second group of fibers. Accordingly, for each fiber in the first group, there can be a fiber in the second group of identical appearance. The first and second fiber groups described in this specification can each accordingly include, for example, twelve optical fibers in the 12-color sequence of blue, orange, green, brown, slate, white, red, black, yellow, purple, rose, and aqua, without either group of fibers requiring additional identifying indicia such as stripes, etc. According to one embodiment, a fiber optic cable according to the present embodiments can include 24 fibers of 0.25 mm outer diameter and the cable outer diameter can be approximately 3.3 mm or less. Skew performance of the optical fibers for the cable disclosed herein may be at least 3.75 Pico-seconds per meter (ps/m) to satisfy the requirement for high data rate applications. 
     Although the strength members disclosed herein are illustrated at particular locations within a cable (i.e. the cable center, toward the cable periphery), the strength members may be disposed within a cable at any location. The strength members may be strands of aramid (e.g., Kevlar®) yarn or other appropriate high tensile strength materials. 
     The cable jackets disclosed herein may be manufactured from any suitable material and may depend on the particular application and/or application space. For example, polyvinylchloride (PVC), chlorinated polyethylene (CPE) or flame retardant polyethylene (FRPE) may be used and fluoropolymers such as polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE) may be used as well. Depending on the burn requirements, nylons, polyesters, polyethylene (PE), or polypropylene (PP) may be used. 
     Fiber optic cables having a dual cavity design (e.g. cables  10 ,  30 ,  50 ,  90 ,  110 ) may be extruded in a fashion similar to known zipcord cables; however, a round die may be necessary to fabricate the desired cross-sectional shape. Furthermore, the shape of a die tip may determine the cross-sectional shape of the cavity. The size of each cavity can be extruded so that it is sufficient to accommodate twelve colored fibers and at least two ends of aramid yarn. 
     It will be apparent to those skilled in the art that various other modifications and variations can be made without departing from the spirit or scope of the present disclosure.