Patent Publication Number: US-2001000139-A1

Title: Fiber optic cable for installation in a cable passageway and methods and an apparatus for producing the same

Description:
RELATED APPLICATIONS  
     1. The present invention is a Continuation-in-Part of U.S. Ser. No. 08/869,819, which is incorporated by reference herein.  
    
    
     
       FIELD OF THE INVENTION  
       2. The present invention relates to a fiber optic cable that is suitable for installation in a cable passageway.  
       BACKGROUND OF THE INVENTION  
       3. Conventional fiber optic cables include optical fibers which are capable of transmitting voice, video, and data information. A fiber optic cable should have a craft-friendly construction which permits ease of installation. Installation of a fiber optic cable typically requires the pulling of the cable through a cable passageway. The cable passageway can be, for example, a duct, a tube, a cable enclosure, building structural features, a trough, a tunnel, a tray, a trunk, a manhole, a handhole, a fingerhole, or a splice box.  
       4. The ease with which a fiber optic cable is installed in a cable passageway may be dependent on certain characteristics of the fiber optic cable. For example, surface area contact between the cable jacket, which is typically of the circular profile type, and surface areas in the cable passageway causes frictional resistance to the cable pulling force. Resistance to the cable pulling force can be a limiting factor regarding the length or ease of the cable to be pulled. Such resistance may also be a function of the coefficient of friction of the cable jacketing material. Additionally, a light-weight cable is generally easier to pull than a heavy cable. Cable flexibility is a factor as the use of stiff cable components makes the cable difficult to bend during the cable pulling operation. Cable size is also a factor as a cable with a small cross sectional area is generally easier to pull through a narrow passageway than a cable with a large cross sectional area. Moreover, apart from ease of installation, the cost per unit length of the cable may be an important factor in deciding between commercially available fiber optic cables.  
       5. Taking the foregoing factors into consideration, fiber optic cable designs having circular profile jackets are part of the background of the present invention. For example, a fiber optic cable which may be difficult to route through a passageway is disclosed in U.S. Pat. No. 5,029,974. The cable includes two steel strength members embedded in a circular profile cable jacket. The steel strength members are designed to resist axial compression due to, for example, aging shrinkage or thermal contraction of the cable jacket. The use of steel strength members creates a spark hazard and their weight may negatively affect the cable pulling operation. Additionally, the circular profile jacket can present a substantial degree of surface area contact and friction with the cable passageway that can result in substantial resistance to a cable pulling force.  
       6. Additionally, fiber optic cable designs having non-circular profile jackets may be difficult to install in cable passageways. For example, the cable disclosed in U.S. Pat. No. 4,844,575 is of the composite cable type and includes an oval profile cable jacket. The oval profile can present a substantial amount of surface area contact with the cable passageway, and the weight of the cable can make it difficult to install in a cable passageway.  
       OBJECTS OF THE INVENTION  
       7. It is an object of the present invention to provide a fiber optic cable that is easy to install in a cable passageway.  
       8. It is another object of the present invention to provide a fiber optic cable that is of a light weight and presents minimal resistance to a cable pulling force during installation.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     9.FIG. 1 is a cross-sectional view of a fiber optic cable component according to the present invention.  
     10.FIG. 2 is a cross-sectional view of a fiber optic cable component according to the present invention.  
     11.FIG. 3 is an isometric view of the fiber optic cable component of FIG. 2.  
     12.FIG. 4 is a cross-sectional view of a fiber optic cable according to the present invention.  
     13.FIG. 5 is a schematic view of an apparatus for forming a fiber optic cable component according to the present invention.  
     14.FIG. 6 is a cross sectional view of a fiber optic cable according to the present invention.  
     15.FIG. 7 is an isometric view of an extrusion unit for extruding a cable jacket of fiber optic cables of the present invention.  
     16.FIG. 8 is a cross-sectional view of a fiber optic cable component according to the present invention.  
     17.FIG. 9 is an isometric view of a fiber optic cable according to the present invention.  
     18.FIG. 10 is an isometric view of a fiber optic cable according to the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     19. Referring to FIGS.  1 - 4 , an exemplary easy to install fiber optic cable  40  according to the present invention will be described. Fiber optic cable  40  includes a fiber optic cable component  10 , for example, a slotted core. Component  10  can include optical fiber ribbons  42  or individual optical fibers (not shown) disposed in features of a rod  11 , for example, recesses  13 . Rod  11  can be surrounded by a wrapping tape  47  (FIG. 4) and binders (not shown), a water swellable tape or barrier, and/or an armor layer. To minimize cable pulling force, fiber optic cable  40  can include a low pulling resistance cable jacket  45  having a profile including surface irregularities. The surface irregularities of cable jacket  45  can be in the form of, for example, an undulated profile  46 . In addition, cable jacket  45  can include a friction reducing additive, described in more detail hereinbelow. Profile  46  can include crests  46   a  and hollows  46   b  that have generally arcuate surfaces, but profile  46  may include some flat sections. In general, however, crests and hollows  46   a , 46   b  can define a sinusoidal-like cross-sectional circumference, e.g., as compared to a circular profile R (FIG. 4), which circumference can be substantially aligned with the center of fiber optic cable  40 .  
     20. As noted above, fiber optic cables of the present invention can include a fiber optic cable component  10 . Alternatively, a fiber optic cable of the present invention can include an exemplary component  10 ′ (FIG. 2) or  10 ″ (FIG. 8). Fiber optic cable components  10 , 10 ′, 10 ″ are of a light weight construction, thereby making cables of the present invention easier to install in a cable passageway. Respective rods  11  of components  10 , 10 ′, 10 ″ may include a central member, for example, a steel strength member  16  with one or more stranded wires. Alternatively, strength member  16  can be a glass or aramid yarn reinforced plastic member, or a combination of glass and aramid yarn. Rod  11  can be cellularized with gas-filled cells, for example, discrete cells  11   a  in a single layer of plastic. The cellularized structure of rod  11  reduces the overall density thereof and reduce the weight of the fiber optic cable in which it is installed. Alternatively, fiber optic cables made according to the present invention can include a multi-layer fiber optic cable component  10 ′ including a non-cellularized inner layer  12  and a cellularized outer layer  14  (FIG. 2). Either or both of the layers  12 , 14  may be cellularized. For example, as shown in FIG. 8, fiber optic cable component  10 ″ includes an inner layer  12  that is cellularized, and an outer layer  14  that has little or no cellularization. Inner layer  12  may be, for example, cellularized to about a 5% to 50% density reduction or higher. Layers  12 , 14  may be the same or different materials, and the layers can be coextruded or extruded sequentially. Additionally, a rod  11  according to the present invention may include a plastic skin  11   b  (FIG. 2) formed of, for example, a material having a suitable modulus, e.g. high or medium density polyethylene. The plastic skin can be co-extruded or extruded subsequently with the rod material. Skin  11   b  improves the strength, smoothness, and water impermeability of rod  11 .  
     21. The cellularized structure of rod  11  according to the present invention may be formed by the mixing of a polymeric material with a cellularizing agent. The cellularizing agent may, for example, include: a conventional pre-mixed chemical foaming agent; a gas dissolved in the melt under high pressure which becomes expands upon a pressure drop after the extrusion process; or a volatile liquid dissolved in the melt which will change into a gas at the high temperature of the melt after the extrusion process when the pressure returns to atmospheric. An example of a suitable chemical foaming agent is a Celogen AZNP130 agent made by Uniroyal. An example of a suitable pre-mixed chemical foaming agent is a DHDA8885 material made by Union Carbide. Alternatively, the cellularizing agent may comprise solid or hollow particles formed of glass microspheres, carbon, metal, ceramics, polymers, or resins singly or in mixtures to achieve one or more of the advantages of the invention. Selected gas or chemical cellularizing agents should have a low diffusion rate in the material. Preferred conventional polymeric materials for rod  11  include polyolefins, for example, polypropylene, polyethylene, or blends thereof. In addition, rod  11  may be cellularized by injecting a cellularizing agent comprising a compressed gas or a volatile liquid material into the extruder during the extrusion process. Suitable materials for injection into the extruder comprise butane, pentane, nitrogen, and hexane.  
     22. The invention may also be practiced in the form of a fiber optic cable  50  (FIG. 6) including a component  10  having, for example, four-fiber ribbons  52  disposed in fifteen slots  53  of a cellularized rod  51 . Cellularized rod  51  can be surrounded by a wrapping tape  54  and binders (not shown). Cable  50  can include a cable jacket  55  having an undulated profile  56 . The surface irregularities of cable  50  can be configured so that at least two crests  56   a  will support the cable on, e.g., a curved surface  60 , or virtually any surface of or in a cable passageway, so that at least one hollow  56   b  is between the crests, thereby minimizing the surface area contact between cable jacket  55  and surface  60 .  
     23. Cable jackets  45 , 55  can be formed of a suitable plastic material, for example polyethylene, and, to reduce resistance to a cable pulling force, can include a friction reducing additive therein. The friction reducing additive can function by migrating to the surface of cable jackets  45 , 55  and lubricating the interface between the cable jackets and virtually any surface of or in the cable passageway. The friction reducing additive can be of the type of material that is essentially non-compatible with the cable jacket material. Examples of suitable friction reducing additives include fatty acids compounds or derivatives, e.g., glycerol mono-stearate, stearic acid, or a fatty amide wax (e.g. as sold by Witco under the tradename Kenamide). Additional examples of suitable friction reducing additives include silicone oils, fluoro-compounds (e.g. Viton), and mineral oils. In addition, the additive may be an inorganic filler, e.g., glass microspheres or talc. The friction reducing additive may be singly compounded with the cable jacket material, or mixtures of additives may be used as well.  
     24. Referring now to FIG. 5, an exemplary manufacturing line  30  for making exemplary fiber optic cable component  10  according to the present invention will be described. Manufacturing line  30  includes: a pay-off reel  18 ; a crosshead  20 ; a rotary die  22 ; a cooling trough  24 ; a capstan  25 ; and a take-up reel  26 . Rotary die  22  includes a die profile that corresponds to the desired shape of component  10  including, for example, recesses  13 . The extrusion temperature of cross-head  20  can be set at about 140° C. or below to about 200° C. or above.  
     25. In operation of manufacturing line  30 , strength member  16  is fed from a reel  18  into cross-head  20 . Cross-head  20  encloses a melt mixture comprising a plastic material and a cellularizing agent, the agent can be added to the material in the extruder barrel or can be pre-mixed with the material prior to entry into the extruder. As strength member  16  passes through cross-head  20 , the melt mixture is extruded thereon. During this process, rotating or stationary die  22  shapes the melt into a rod  11 . Rod  11  can be rotated while the die is stationary to form recesses of a helical or an alternating pitch. Typically, a foaming agent is incorporated into the polymer to produce a foamed plastic material which is up to about, for example, 50% or more gas-filled cells. Closed cells are the preferred cell configuration of the present invention., Next, cooling trough  24  cools rod  11  into a solid fiber optic cable component  10 . Fiber optic cable component  10  is pulled by capstan  25  and is then received by a take-up reel  26 . As noted above, to produce a two-layer spacer rod as shown in FIG. 2, first layer  12  and second layer  14  can be coextruded about strength member  16 , or extruded sequentially in separate extrusion operations (not shown).  
     26. Components  10 , 10 ′, 10 ″ can be fed into a fiber optic cable manufacturing line where optical fiber ribbons  44 , 52  or individual optical fibers can be stranded into respective recesses  13 , 53 . Profiles  46 , 56  may be formed with an exemplary extrusion unit  100  (FIG. 7). Extrusion unit  100  includes a die  101  with a profile  102  cut therein including channels  102   a  and ridges  102   b  that extend longitudinally into the die and form the crests and hollows  46   a , 46   b ; 56   a,   56   b  of profiles  46 , 56 . Die  101  can be stationary relative to a frame  104 , or mounted through a bearing  105  which permits relative rotational movement between die  101  and frame  104 . Where it is desired to rotate die  101 , the die can be operatively connected to and rotated by a rotation driving mechanism (not shown). Frame  104  includes an inlet port  106  for supplying jacketing material to die  101 .  
     27. In an exemplary operation of extrusion unit  100 , rods  11 , 51  with tapes  47 , 54  therearound are fed into the inlet  51  side of die  100  as a jacketing material is supplied under suitable temperature and pressure conditions to inlet port  106 . The jacketing material is then extruded onto and around tapes  47 , 54 , and, as the cable jacketing material is expressed through die  101 , cable jackets  45 , 55  take the shape of profile  102 . The channels  102   a  and ridges  102   b  of profile  102  create the crests and hollows  46   a , 46   b ; 56   a,   56   b  of profiles  46 , 56 . Profile  102  can be shaped to create a repeating cycle of crests and hollows in a cable jacket, at a given angular period relative to a center of the cable, for example, as shown by angle α (FIG. 6). The magnitude of angle α may range from, as a rough example, 5 to 50 degrees or more. The repeating cycle of crests and hollows may be symmetrical about the center of the cables.  
     28. Die  101  may be stationary relative to frame  104  so that profiles  46 , 56  are parallel to the axis of the cable, or die  101  may be completely or alternately rotated to create continuous or intermittent helical or SZ shaped profiles  46 , 56 . The rotation driving mechanism can be operatively connected to a controller which compels the desired motion output. The controller can be operatively associated with helix or switchback sensors, as disclosed in U.S. Pat. No. 5,729,966 and U.S. Ser. No. 08/873,511 both of which are incorporated by reference herein, so that the die  100  can form helical or SZ shaped profiles  46 , 56 . In this way, the shape of the profiles  46 , 56  can include a helical or SZ configuration that exactly or roughly traces the helical or SZ recesses  13  of components  10 , 10 ′, 10 ″ (FIGS. 3,  9  and  10 ). In the case of SZ profiles  46 , 56 , the locations of the switchbacks of the grooves  13  in components  10 , 10 ′, 10 ″ can be inferred from observing the SZ configuration of profiles  46 , 56  formed in cable jacket  45 , 55 . Alternatively, die  101  can remain stationary while rods  11 , 51  are completely or alternately rotated to create helical or SZ shaped profiles  46 , 56  in cable jackets  45 , 55 . The disclosure of U.S. Pat. No. 4,548,567, which discloses a rotating die for use with slotted core members, is incorporated by reference herein.  
     29. Component  10 , 10 ′, 10 ″ of the present invention have many advantages, for example, fiber optic cables made according to the present invention can be light in weight and/or have a low resistance to cable pulling forces. For example, since rod  11  can include one or more layers having a cellularized structure, fiber optic cable components  10 , 10 ′, 10 ″ can be relatively lighter for a given diameter. Because of the relatively lower weight, greater lengths of cables made according to the present invention can be put on a reel. Additionally, cellularized rods made according to the present invention use less plastic material realizing a cost savings. Another advantage is that since cable components  10 , 101 , 101 , can include gas filled cells, the amount of fuel that the cable provides in a fire can be lessened, so that the flame retardant cable jacket can be thinner, resulting in a still smaller, lighter, and less costly cable. Alternatively, a less costly flame retardant jacketing compound can be used. Moreover, profiles  46 , 56  present a minimized surface area contact to a cable passageway, i.e., two crests can rest on a cable passageway with at least one hollow therebetween. In other words, crests according to the present invention are shaped to define substantially narrowed contact interfaces with a cable passageway surface or other surfaces in a cable passageway, e.g., other cables, thereby minimizing surface area contact for providing low resistance to cable pulling forces and ease of installation.  
     30. Persons of ordinary skill in the art will appreciate that the foregoing embodiments of the present invention are intended to be illustrative of the inventive concepts rather than limiting. Moreover, persons of skill in the art will understand that variations can be made to the present invention without departing from the scope of the appended claims. For example, although recesses  13  comprise a generally rectangular cross sectional shape, they may comprise such other cross sectional shapes as are suitable for receiving optical ribbons or fibers. Moreover, as shown in FIG. 3, the lay of recesses  13  may be helical; other lay configurations may be used as well, for example, an S-Z stranded lay configuration. Although the surface irregularities of cable jacket  45  have been described with reference to an undulated profile, the skilled artisan will appreciate that other surface irregularities can be used that will exhibit a suitably low resistance to a cable pulling force, for example: an apex of any of the crests or hollows may be more sharply defined to roughly come to a rounded-off point, can be more rounded than shown in the drawing figures, or can be truncated with flat zones. In addition, the surface irregularities can include, e.g., dimple-like indentations, a saw-tooth configuration, ripples, teat-like extensions, lines, grooves, etc. In addition, profiles  46 , 56  may be modified to include step-like or additional sinusoidal shapes modifying the basic sinusoidal profile. The profiles of cable jackets made according to the present invention, although shown as having a center coincident with the center of the cable, can be eccentric with respect to the center of the cable. The profiles  46 , 56  of the present invention can roughly approximate a sinusoidal wave, or they can approximate a sinusoidal function with mathematical precision within a nominal range. In addition, rather than being symmetrical, profiles  46 , 56  can include an asymmetrical configuration. Although the embodiments presented hereinabove discuss components of the slotted core type, skilled artisans will appreciate that cable jackets  46 , 56  can be applied over other types of fiber optic cable components which require cable jackets, for example, components of the core tube, buffer tube, fiber bundle, or optical ribbon types having a parallel, helical, or SZ feature. Fiber optic cables made in accordance with the present invention can be used with a standard pulling attachment.