Abstract:
Cables have dielectric armors with armor profiles that provide additional crush and impact resistance for the optical fibers and/or fiber optic assembly therein, while retaining flexibility to aid during installation. The armored cables recover substantially from deformation caused by crush loads.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 13/089,296, filed Apr. 18, 2011, and claims the benefit of U.S. Prov. App. No. 61/327,335, filed Apr. 23, 2010, the entire contents of which are hereby incorporated by reference. 
         [0002]    This application is related to U.S. application Ser. No. 12/261,645, filed Oct. 30, 2008, now U.S. Pat. No. 7,702,203, U.S. Prov. App. 61/174,059, filed Apr. 30, 2009, and U.S. application Ser. No. 12/748,925, filed Mar. 29, 2010 and published as U.S. 2010/0260459. 
     
    
     TECHNICAL FIELD 
       [0003]    The present disclosure relates generally to optical fiber assemblies, and in particular relates to armored fiber optic assemblies having dielectric armor. 
       BACKGROUND 
       [0004]    Fiber optic cables and assemblies should preserve optical performance when deployed in the intended environment while also satisfying any other requirements for the environment. Indoor cables for riser and/or plenum spaces, for example, may require certain flame-retardant ratings as well as mechanical requirements. Mechanical characteristics such as crush performance, permissible bend radii, and temperature performance in part determine how installation and use of the cable in the installation space affect optical performance of the cable. 
       SUMMARY 
       [0005]    According to a first embodiment, an armored fiber optic assembly comprises a fiber optic assembly having at least one optical fiber and a dielectric armor surrounding the fiber optic assembly. The dielectric armor comprises an inner dielectric layer surrounding the fiber optic assembly, and an outer dielectric layer wound around the inner layer and bonded thereto. 
         [0006]    According to a second embodiment, an armored fiber optic assembly comprises a fiber optic assembly having at least one optical fiber and a dielectric armor surrounding the fiber optic assembly. The dielectric armor comprises an inner dielectric layer spirally wound around the fiber optic assembly, wherein the outer layer has the shape of a strip; and an outer dielectric layer surrounding the inner layer and bonded thereto, wherein the outer layer has an armor profile. 
         [0007]    According to a third embodiment, a method of forming an armored fiber optic assembly comprises providing a fiber optic assembly comprising at least one optical fiber, extruding an inner layer of a dielectric armor around the fiber optic assembly, wherein extruding the inner layer comprises diverting a flow of an inner extrusion material with a first profiling feature to form a spiral strip, and extruding an outer layer of the dielectric armor around the inner layer from an outer extrusion material that is less rigid than the inner extrusion material, wherein the outer layer becomes at least partially bonded to the inner layer. 
         [0008]    According to a fourth embodiment, a method of forming an armored fiber optic assembly comprises providing a fiber optic assembly comprising at least one optical fiber, extruding a first layer of a dielectric armor around the fiber optic assembly, wherein extruding the first layer comprises diverting a flow of a first extrusion material with a first profiling feature rotating in a first direction, and extruding a second layer of a dielectric armor around the fiber optic assembly, wherein extruding the second layer comprises diverting a flow of an second extrusion material with a second profiling feature rotating in a second direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings are included to provide further understanding of the invention. The drawings illustrate the various example embodiments of the invention and, together with the description, serve to explain the principals and operations of the invention. 
           [0010]      FIG. 1  is a perspective view of a first example embodiment of an armored fiber optic assembly having a dielectric armor. 
           [0011]      FIG. 2  is a schematic cross-sectional view of an explanatory extrusion system for making armored fiber optic assemblies. 
           [0012]      FIG. 3  is a perspective view of a second example embodiment of an armored fiber optic assembly. 
           [0013]      FIG. 4  is a schematic cross-sectional view of an explanatory extrusion system for making armored fiber optic assemblies. 
           [0014]      FIG. 5  is a perspective view of a third example embodiment of an armored fiber optic assembly. 
           [0015]      FIG. 6  is a perspective view of a portion of an extrusion die that can be used to form the fiber optic assembly of  FIG. 5 . 
           [0016]      FIG. 7  is a perspective view of a fourth example embodiment of an armored fiber optic assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Reference is now made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Whenever possible, identical or similar reference numerals are used throughout the drawings to refer to identical or similar parts. 
         [0018]      FIG. 1  is a perspective cut-away view of an armored fiber optic assembly  120  including a core fiber optic assembly  30  disposed within a dielectric armor  150 . The dielectric armor  150  is non-conductive and has an outer surface  152  that includes an armor profile  154  generally formed in a spiral along a longitudinal axis. As used herein, “armor profile” means that the outer surface has an undulating surface along its length that looks similar to conventional metal armors (i.e., a undulating shape along the length of the armor). The dielectric armor  150  is advantageous in that it both provides crush resistance and recovers to assume its original shape when subjected to crush loads. The dielectric armor  150  may also meet flame and/or smoke ratings, and does not require electrical grounding. 
         [0019]    The dielectric armor  150  includes an inner layer  162  and an outer layer  164  disposed on the outer surface of the inner layer  162 . According to one aspect of the present embodiment, the inner layer  162  can have the shape of a spiral “strip” that winds around the core fiber optic assembly  30 . The outer layer  164  can be a continuous cover or coating over the exterior of the inner layer  162 . The inner layer  162  can be more rigid than the outer layer  164 . Accordingly, the Shore D hardness of the inner layer  162  can be more than the Shore D hardness of the outer jacket layer  164 . An inner surface  166  of the inner layer  162  may also have an armor profile. 
         [0020]    In the illustrated embodiment, the outer layer  164  has a “continuous annular cross-section”. As used herein, “continuous annular cross-section” means there are no spiral grooves, openings, or slits that cut entirely through the layer  164 . The exemplary inner layer  162  has the form of a strip wound around the core fiber optic assembly  30 . The outer layer  164  can be extruded directly onto the inner layer  162  so that the two layers are bonded or adhered together. The inner layer  162  may be constructed of a relatively rigid polymer, while the outer layer  164  can be relatively less rigid. The relatively rigid inner layer  162  accordingly provides tensile strength, resistance to crush, and other robust properties. However, because the inner layer  162  has the shape of a spiral strip, and because the outer layer  164  can be relatively less rigid, the armored fiber optic assembly  120  can be relatively flexible and easy to bend. The thickness, width, and composition of the “strip” that forms the inner layer  162  can be selected to provide desirable mechanical properties. In general, the outer layer  164  completely covers the inner layer  162 . The fiber optic assembly  30  is housed within and protected by the dielectric armor  150 . 
         [0021]    In the illustrated embodiment, the fiber optic assembly  30  is a fiber optic cable having an extruded polymer cable jacket  90  and a plurality of tight-buffered optical fibers  94  extending longitudinally through the assembly  120  within the cable jacket  90 . Strength elements (not shown), such as aramid fibers, may also extend longitudinally through the cable jacket  90 . In one embodiment, the cable jacket  90  can be omitted. The armor  150  need not be secured to the core assembly  30  and may be separated from the core assembly  30  by a free space or separation distance. An average or median separation ΔR can therefore be calculated as ΔR=RI−RC, where RI is the average inside radius of the armor, and RC is the average outside radius of the core assembly. 
         [0022]    The armor  150  can be formed by coextrusion methods. For example, the extrudate materials for the respective layers enter the extrusion tooling together, and may become strongly bonded together as the two extrudate materials solidify. The armor  150  can be essentially a unitary one-piece armor of two strongly bonded polymer materials, with a cross-section of the armor shown in U.S. application Ser. No. 12/748,925, filed Mar. 29, 2010 and published as U.S. 2010/0260459, and may have the same or similar values for pitch, band thickness and other dimensions.  FIG. 2  is a close-up, partial cross-sectional schematic view of an explanatory crosshead  204  used to armor fiber optic assemblies, as viewed in the Y-Z plane, that can be used to form the inner spiral layer  162  of the assembly shown in  FIG. 1 . The crosshead  204  includes a tip  248  having a central channel  250  with an output end  252  and in which is arranged a profile tube  260  having an outer surface  261 , an inner surface  262  that defines a tube interior  263 , a proximal (output) end  264 , and a distal end  265 . A profiling feature  270  is located on outer surface  261  at output end  252 . In an example embodiment, the profiling feature  270  is a protrusion such as a nub or a bump. The profile tube interior  263  is sized to accommodate the fiber optic assembly  30  as it advances axially through the interior  263 . The profile tube distal end  265  is centrally engaged by a gear  274  that, in turn, is driven by a motor (not shown) in a manner such that the profile tube  260  rotates within channel  250 . 
         [0023]    The crosshead  204  further includes a die  278  arranged relative to the tip  248  to form a cone-like material channel  280  that generally surrounds the central channel  250  and that has an output end  282  in the same plane as channel output end  252 . The material channel  280  is connected to the extruder interior  201  so as to receive extrusion material  232  therefrom and through which flows the extrusion material during the extrusion process to form the inner spiral layer  162 . In the example embodiment of the crosshead  204  of  FIG. 2 , a profile tube output end  265  extends beyond the channel output end  252  such that the profiling feature  270  thereon resides adjacent material channel output end  282 . In an example embodiment, the profile tube  260  and the tip  248  are integrated to form a unitary, one-piece tool. 
         [0024]    In forming armored fiber optic assemblies, extrusion material (not shown) flows through the material channel  280  and out of the material channel output end  282 . At the same time, the fiber optic assembly  30  is fed through the profile tube interior  263  and out of profile tube output end  864  (and thus through the tip  248  and the die  278 ). In the meantime, the profile tube  260  is rotated via the gear  274  so that profiling feature  270  redirects (i.e., shapes) the flow of the extrusion material as it flows about fiber the optic assembly  30 . As the fiber optic assembly  30  moves through the profile tube output end  264 , the circular motion of the profiling feature  270  diverts the flow of extrusion material. The combined motion of the profiling feature  270  and the linear motion of fiber optic assembly  30  forms the spiral strip  162 . The speed at which profile tube  260  rotates relative to the motion of fiber optic assembly  30  (which may also be rotating) dictates the pitch of the spiral strip  162 . The axial position of the profiling feature  270  in relation to the material channel output end  282  can be varied as the feature rotates in order to, for example, form varying gaps between adjacent portions of the spiral strip  162 . 
         [0025]    To form the outer layer  164 , a second, conventional extrusion head (not shown) can be arranged downstream and adjacent to the assembly shown in  FIG. 2 . The second extrusion head can apply a continuous outer jacket layer of non-conductive polymer material over the spiral strip inner layer  162 . 
         [0026]      FIG. 3  is a perspective cut-away view of an armored fiber optic assembly  320  including a core fiber optic assembly  30  disposed within a dielectric armor  350 . The dielectric armor  350  is non-conductive and has an outer surface  352  that includes an armor profile  354  generally formed in a spiral along a longitudinal axis. The dielectric armor  350  is advantageous in that it both provides crush resistance and recovers to assume its original shape when subjected to crush loads. The dielectric armor  350  may also meet flame and/or smoke ratings, and does not require electrical grounding. 
         [0027]    The dielectric armor  350  includes an inner layer  362  and an outer layer  364  disposed on the outer surface of the inner layer  362 . According to one aspect of the present embodiment, the outer layer  364  can have the shape of a spiral “strip” that winds around the exterior of the inner layer  362 . The inner layer  362  can be less rigid than the outer, spiral layer  364 . Accordingly, the Shore D hardness of the inner layer  362  can be less than the Shore D hardness of the outer jacket layer  364 . An inner surface  366  of the inner layer  362  may also have an armor profile. 
         [0028]    In the illustrated embodiment, the inner layer  362  has a continuous annular cross-section. The exemplary outer layer  364  has the form of a strip wound around the inner layer  362  so that portions of the inner layer  362  are visible. The outer layer  364  can be extruded directly onto the inner layer  362  so that the two layers are bonded or adhered together. The outer layer  364  may be constructed of a relatively rigid polymer, while the inner layer  362  can be relatively less rigid. The relatively rigid outer layer  364  accordingly provides tensile strength, resistance to crush, and other robust properties. However, because the outer layer  364  has the shape of a spiral strip, and because the inner layer  362  can be relatively less rigid, the armored fiber optic assembly  320  can be relatively flexible and easy to bend. The thickness, width, and composition of the “strip” that forms the outer layer  364  can be selected to provide desirable mechanical properties. In general, the outer layer  364  covers at least one quarter of the surface area of the inner layer  362 . The fiber optic assembly  330  is housed within and protected by the dielectric armor  350 . 
         [0029]    In the illustrated embodiment, the fiber optic assembly  330  can be similar to the core assembly  30  shown in  FIG. 1 , and may be separated from the core assembly  330  by a free space or separation distance. An average or median separation ΔR can therefore be calculated as ΔR=RI−RC, where RI is the average inside radius of the armor, and RC is the average outside radius of the core assembly. 
         [0030]    As an alternative to the outer layer  364  only covering certain portions of the inner layer  362 , the outer layer could cover the entirety of the inner layer  362 . Further, the inner layer  362  can have the form of a spiral strip wound around the fiber optic assembly, with the outer layer  364  filling in gaps in the wound strip, as well as covering the exterior of the inner layer  364 . The outer layer  364  can be less rigid than the inner layer  362  so that the resultant armored assembly has desirable bend properties. 
         [0031]    As another alternative, to two layers  362 ,  364  can be interlocked spirals wound in the same direction. The armor  350 , comprised of the two interlocked spirals, would have a continuous annular cross section. The interlocked spirals can have a continuous annular cross section with an armor profile. The armor  350  can be formed by coextrusion methods. For example, the extrudate materials for the respective layers enter the extrusion tooling together, and may become strongly bonded together as the two extrudate materials solidify. The armor  350  can be essentially a unitary one-piece armor of two strongly bonded polymer materials, with a cross-section of the armor shown in U.S. application Ser. No. 12/748,925, filed Mar. 29, 2010, and may have the same or similar values for pitch, band thickness and other dimensions. 
         [0032]      FIG. 4  is a perspective view of an explanatory extrusion apparatus  400 , that can be used to form the inner and outer armor layers. The extrusion apparatus  400  includes a first extrusion head  404  and a second extrusion head  406  that can be arranged end-to-end with the first head  404 . In the exemplary embodiment, the first extrusion head  404  includes a profiling feature  470  that can rotate in order to form varying gaps in a flow of extrudate to form a spiral strip. In such an application, the first extrusion head  404  would typically form the inner armor layer. Therefore, in the arrangement of  FIG. 4 , the fiber optic assembly shown in  FIG. 1  could be produced by the apparatus  400  by extruding the inner, spiral strip layer  162  formed by the extrusion head  404 , and the outer continuous layer  164  formed over the inner layer  162  by the second extrusion head  406 . The illustrated second extrusion head  406  does not include a profiling feature and can be conventional in form and operation. 
         [0033]    The extrusion apparatus  400  can be modified to form the fiber optic assembly  320  as shown in  FIG. 3 . In this application, both the first extrusion head  404  and the second extrusion head  406  would be equipped with profiling features. The first extrusion head  404  would form the inner layer  362  with a continuous armor profile. The second extrusion head  406  would form the outer, spiral strip layer  364  over the continuous inner layer  362  by interrupting the flow of extrudate to form a spiral strip over the inner layer. While the extrusion apparatus  400  is shown as two separate heads  404 ,  406 , it could be combined as a single, “coextrusion” head that is capable of forming two or more dielectric layers. 
         [0034]      FIG. 5  is a perspective cut-away view of an armored fiber optic assembly  520  including a core fiber optic assembly  30  disposed within a dielectric armor  550 . The dielectric armor includes a tubular portion  552  and a pair of rod-like elongated rails  554  extending along each side of the armor  550 . The tubular portion  552  has an outer surface  562  having an armor profile  564  generally formed in a spiral along a longitudinal axis. An inner surface  566  of the armor  550  may also have an armor profile. In the illustrated embodiment, the armor  550  has a continuous annular cross-section. 
         [0035]    The tubular portion  552  is illustrated as comprising a single layer of dielectric material. The tubular portion  552  can be similar in cross-section to the armor shown in U.S. application Ser. No. 12/748,925, filed Mar. 29, 2010, and may have the same or similar values for pitch, band thickness and other dimensions. The inclusion of the rails  554 , however, provides increased tensile strength, allowing reduced thickness of the tubular portion  552 . The rails  554  are shown as having rectangular sections on the sides of the rails distal to the armor center. Other cross-sections, however, such as curved, oval, arcuate, etc. may also be used for the elongate rails  554 . The armor  550  need not be secured to the core assembly  30  and may be separated from the core assembly  30  by a free space or median separation distance. The rails  554  and the tubular portion  552  can be extruded from a common extrudate material in the same crosshead and can form a uniform, continuous piece.  FIG. 6  is a close-up, partial cross-sectional schematic view of an explanatory profiling die  602 . The die  602  can be used in place of the die  278  ( FIG. 2 ), for example, to form the elongate rails  554  of the armored fiber optic assembly  520 . The channels  608  on either side of the die  602  allow additional extrudate to flow on the sides of the armor to form the elongate rails. The rails need not be continuous, and can be interrupted so that a series of rails are attached to the tubular portion. All or some rails could alternatively be located on the inside of the tubular portion  552 . 
         [0036]      FIG. 7  is a perspective cut-away view of an armored fiber optic assembly  720  including a core fiber optic assembly  30  disposed within a dielectric armor  750 . The dielectric armor includes a first spiral portion  752  and a second spiral portion  754  that are wound in opposite directions and that intersect one another. The spiral portions  752 ,  754  have the form of spirally round flat strips of generally rectangular cross section. The counterwound spiral form of the armor  750  provides flexibility to the armor that also prevents the spiral portions  752 ,  754  from collapsing onto the core assembly  30 . The armor  750  need not be secured to the core assembly  30  and may be separated from the core assembly  30  by a free space or separation distance. The armor  750  includes generally diamond shaped, curved openings  760  through which the core assembly is visible. This armor  750  can be formed by two counterrotating profiling projections. For example, in the configuration shown in  FIG. 4 , both extrusion crossheads  404 ,  406  could be provided with profiling features arranged to form spiral strips that rotate in opposite directions and overlap. Alternatively, the openings  760  can be formed in the armor by intermittently blocking the flow of extrudate. 
         [0037]    By way of example, the core fiber optic assemblies  30 ,  330  discussed in the context of the above-described embodiments may be a stranded tube cable, monotube cable, micromodule cable, slotted core cable, loose fibers, tube assemblies, or the like. Additionally, fiber optic assemblies according to the present embodiments can include any suitable components such as water-blocking or water-swelling components, flame-retardant components such as tapes, coatings, or other suitable components. The fiber optic assembly  30  may have any suitable fiber count such as 6, 12 or 24-fiber MIC® cables available from Corning Cable Systems of Hickory, N.C. The core assemblies shown in the present embodiments can be separated from the interior surface of the armor by a median separation in the range of about 0.1-1.5 millimeters. Alternatively, the armor can be relatively tightly conforming to the surface of the core assembly. 
         [0038]    The embodiments discussed above may describe specific materials for assembly components to meet desired mechanical and burn characteristics. In general, if intended for indoor use, the armored fiber optic assemblies may be flame-retardant and may have a desired flame-retardant rating depending on the intended space, such as plenum-rated, riser-rated, general-purpose, low-smoke zero-halogen (LSZH), or the like. Suitable polymer materials for the armors may be selected from one or more of the following materials to meet the desired rating: polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), flame-retardant polyethylene (FRPE), chlorinated polyvinyl chloride (CPVC), polytetraflourethylene (PTFE), polyether-ether keytone (PEEK), Fiber-Reinforced Polymer (FRP), low-smoke zero-halogen (LSZH), polybutylene terephthalate (PBT), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PETE), and acrylonitrile-butadiene-styrene (ABS). PVCs available from Teknor Apex under the tradenames FG RE 8015A, 8015B and 8015D may also be used. In this specification, the terms “polymer” and “polymeric” indicate materials comprised primarily of polymers, but allow for the inclusion of non-polymer additives and other materials, such as fire-retardant compounds, etc., and the inclusion of multiple polymers in a blend. The term “polymer” is intended to encompass copolymers, for example. 
         [0039]    It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention.