Patent Publication Number: US-8983254-B2

Title: Optical fiber assemblies

Description:
PRIORITY APPLICATION 
     This application is a continuation of U.S. application Ser. No. 14/041,257, filed Sep. 30, 2013, which is a continuation of U.S. application Ser. No. 13/081,101, filed Apr. 6, 2011, which issued on Oct. 22, 2013 as U.S. Pat. No. 8,565,565 and which is a continuation of International Application No. PCT/US2009/060163, filed Oct. 9, 2009, which claims priority to U.S. Application No. 61/104,142, filed Oct. 9, 2008, and to U.S. Application No. 61/245,420, filed Sep. 24, 2009, the contents of each of which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present application relates generally optical fiber assemblies having low bend radii and small cross-sectional areas. 
     BACKGROUND 
     Communications networks are used to transport a variety of signals such as voice, video, data and the like. As communications applications required greater bandwidth, communication networks switched to fiber optic cables since they are capable of transmitting an extremely large amount of bandwidth compared with copper conductors. Fiber optic cables are also much smaller and lighter compared with copper cables having the same bandwidth capacity. Conventional fiber optic cables, however, may be too large or rigid for some applications. For example, in a multiple dwelling unit (MDU) such as an apartment building, it is often necessary to run fiber optic cables through small spaces and around tight corners to provide access to individual dwelling units. Conventional fiber optic cables often are either too large in cross-section, too inflexible, or both, to be run to individual dwelling units. 
     Conventional MDU deployments also require pulling individual cables from the fiber distribution terminal (FDT) to each living unit. The technician typically unspools a cable down a hallway and then places them into a raceway molding. The raceway can become congested with cables, however, and the technician may be required to pull from 6-12 individual drop cables from the FDT to the living units. The time required to pull off of individual reels can also be disruptive to MDU tenants and add to labor costs of installation. 
     SUMMARY 
     According to one embodiment, a fiber optic assembly comprises a bundled unit of a plurality of single fiber subunit fiber optic cables stranded together. The bundle of subunit fiber optic cables may be wrapped with one or more binders to secure the subunit cables in place. The subunit cables can be SZ stranded to facilitate access to individual subunits. The subunit cables can have flame retardant properties to achieve desired flame ratings for the fiber optic assembly. 
     According to one aspect of the first embodiment, the stranded bundle of subunit fiber optic cables forming the fiber optic assembly does not require a conventional central strength member component, such as a GRP rod, or an outside cable sheath. Omission of the central strength component and/or outer jacket in part gives the fiber optic assembly an extremely small bending radius and a small cross-section. 
     According to another aspect, one or more of the subunit fiber optic cables can have an integral, individual strength component. The strength component can comprise a layer of flexible, loose tensile strength members. Accordingly, the fiber optic assembly incorporating the subunit cables can have extremely high tensile strength, while not being excessively rigid or inflexible such as cables having rigid central strength members. 
     According to yet another aspect, the subunit fiber optic cables can include one or more bend-insensitive optical fibers. The fiber optic assembly can therefore be bent around tight corners, etc. without excessive attenuation losses in the individual optical fibers. In use, the subunit fiber optic cables can be separated from the fiber optical assembly and run to separate locations. The use of bend-insensitive optical fibers allows the subunit cables to be run through extremely tight locations and along tortuous paths. 
     Those skilled in the art will appreciate the above stated advantages and other advantages and benefits of various additional embodiments reading the following detailed description of the embodiments with reference to the below-listed drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features of the drawings are not necessarily drawn to scale. 
         FIG. 1  is a perspective view of a portion of a fiber optic assembly according to a first embodiment of the invention. 
         FIG. 2  is a cross-sectional view of the fiber optic assembly illustrated in  FIG. 1  taken on line  2 - 2  in  FIG. 1 . 
         FIG. 3  is a perspective partial cutaway view of a portion of a subunit fiber optic cable used in the fiber optic assembly illustrated in  FIG. 1 . 
         FIG. 4  is a cross-sectional view of the subunit fiber optic cable illustrated in  FIG. 3  taken on line  4 - 4  in  FIG. 3 . 
         FIG. 5  illustrates bend characteristics of the fiber optic assembly illustrated in  FIG. 1 . 
         FIG. 6  is another depiction of bend characteristics of the fiber optic assembly illustrated in  FIG. 1 . 
         FIG. 7  is a depiction of characteristic dimensions for the fiber optic assembly illustrated in  FIG. 1 . 
         FIG. 8  is a perspective view of a portion of a fiber optic assembly according to a second embodiment of the invention. 
         FIG. 9  is a cross-sectional view of the fiber optic assembly illustrated in  FIG. 8  taken on line  9 - 9  in  FIG. 8 . 
         FIG. 10  is a perspective view of a portion of a fiber optic assembly according to a third embodiment of the invention. 
         FIG. 11  is a cross-sectional view of the fiber optic assembly illustrated in  FIG. 10  taken on line  11 - 11  in  FIG. 10 . 
         FIG. 12  is a plot of delta attenuation in a mandrel wrap test at 1550 nanometers for the cable of  FIGS. 10-11 . 
         FIG. 13  is a plot of delta attenuation in a corner bend test at 1550 nanometers for the cable of  FIGS. 10-11 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  is a perspective view of a portion of a fiber optic assembly  10  or bundled optical cable according to a first embodiment of the invention.  FIG. 2  is a cross-sectional view of the fiber optic assembly  10  taken on line  2 - 2  in  FIG. 1 . Referring to  FIGS. 1 and 2 , the fiber optic assembly  10  comprises a bundled unit of a plurality of subunit fiber optic cables  100 . The subunit cables  100  are wrapped with one or more binders to secure the subunit cables  100  in place. In the illustrated embodiment, a pair of oppositely helically wound outer or external binders  110 ,  114  are wound about the external periphery of the bundle of subunit cables  100 . One or more inner binders can be helically wound about an inner layer  120  of the subunit cables  100 . In the illustrated embodiment, a single inner binder  118  is wound about the three inner subunit cables  100  that constitute an inner layer  120  of subunit cables. The outer layer  130  of subunit cables  100  is constituted by the nine subunit cables surrounding the inner layer  120  in a “9-3” arrangement. 
     In the illustrated embodiment, the subunit cables  100  are SZ stranded together. SZ stranding is advantageous in that it facilitates mid-span access of the subunit cables  100 , and important feature when the cables  100  are to be deployed throughout structures such as multiple dwelling units. The outer binders  110 ,  114  may be contra-helically stranded about the outer layer  130  of subunit cables  100 , and the inner binder  118  may be helically wrapped about the inner layer  120 . In general, the lay length of the helically wrapped external binders  110 ,  114  is smaller than the lay length of the subunit cables  100 , but other suitable lay lengths are possible. The adjoining inner and outer layers  120 ,  130  of subunit cables  100  can be stranded in separate passes on separate stranders, or on a common strander in a single pass. The subunit cables  100  of the inner layer  120  may be immediately adjacent and contacting those of the outer layer  130 , with only the binder  110  being interposed between the layers. 
     The binders  110 ,  114 ,  118  stranded about the subunit fiber optic cables  100  can be made from high tensile strength materials to enhance the tensile strength of the fiber optic assembly  10 . For example, the binders can be formed from elongate tensile yarns, such as aramid, fiberglass, polyester and other tensile yarns. 
       FIG. 3  is a perspective partial cutaway view of a portion of a subunit fiber optic cable  100  used in the fiber optic assembly  10  shown in  FIG. 1 .  FIG. 4  is a cross-sectional view of the subunit fiber optic cable  100  taken on line  4 - 4  in  FIG. 3 . The subunit fiber optic cables  100  can be, for example, flame retardant single fiber cables. In the illustrated embodiment, the subunit fiber optic cable  100  includes a single optical fiber  150  surrounded by a buffer coating  154  applied over the optical fiber  150 . The optical fiber  150  may contain a core and a cladding surrounding the core, with one or more polymer coatings applied over the cladding. A layer  158  of loose tensile strength members surrounds the buffer coating  154 , and an outer polymer tubular subunit jacket or sheath  160  is extruded over the layer  158  of strength members. According to the present embodiments, the layer  158  of loose tensile strength members adds sufficient tensile strength to the individual fiber optic subunits such that additional strength members are not required for the overall assembly  10 . For example, assemblies as disclosed herein can be free of rigid strength members such as glass-reinforced plastic (GRP) rods, which add cost and increase the bend radii of cables. 
     The buffer coating  154  may be formed of a polyvinyl chloride (PVC) material. Other suitable materials for the coating  154  include polymeric materials such as ultraviolet light cured acrylate materials, polyethylene, PVDF, nylon or PVR. The outer subunit jacket  160  may be formed of PVC material, for example. Other suitable materials for the outer subunit jacket  160  include polymeric materials such as polyethylene, PVDF, or nylon. The layer  158  of tensile strength members can be aramid fiber yarns such as KEVLAR® available from E. I. du Pont de Nemours and Co., fiberglass, and aramid-reinforced plastics (ARP). The subunit jacket  160  and/or the coating  154  can include aluminum trihydrate, antimony trioxide, or other suitable additives to improve flame resistance. 
     The optical fibers  150  used in the subunit fiber optic cables  100  may be bend-insensitive optical fibers. Examples of bend-insensitive optical fibers include the ClearCurve™ brand of optical fibers available from Corning Incorporated. Such fibers may have bend radii as low as 5 mm with low attenuation. 
     The fiber optic assembly  10  can have a very small bend diameter while maintaining acceptable attenuation losses.  FIG. 5  illustrates the ability of the fiber optic assembly  10  to be essentially folded back on itself without undue effort. The bend insensitive fibers used in the subunit fiber optic cables  100  can bend at radii of 5 mm, so there is no excess attenuation in the fiber optic assembly  10  in tight bends.  FIG. 6  illustrates winding of the fiber optic assembly  10  around a small-diameter mandrel. The illustrated mandrel has a diameter of about ⅛ inch (3.2 mm). With the extremely tight possible bend configurations of the fiber optic assembly  10 , the assembly is essentially self-limiting in bend characteristics. In other words, the technician installing the fiber optic assembly  10  will not likely be capable of bending the fiber optic assembly in such a way as to induce unacceptable attenuation, and the tightness of the bend diameter is instead determined by the structure of the fiber optic assembly. As used herein, the “bend diameter” induced in a cable or fiber optic assembly can be obtained by wrapping the cable or fiber optic assembly about an elongate element of circular cross-section. The diameter of the elongate element is the bend diameter. 
       FIG. 7  illustrates characteristic dimensions for the fiber optic assembly  10 . In  FIG. 7 , the fiber optic assembly  10  is illustrated as having an idealized cross-sectional area A which is defined by a circle (shown in dashed lines) that encompasses the fiber optic assembly  10 , and a cable diameter CD. The cable diameter CD generally will not be uniform across different parts for the cable cross-section, and may also vary slightly along the length of the fiber optic assembly  10 . An average or mean cable diameter may be measured, for example, by taking several width or thickness measurements along the fiber optic assembly using a micrometer. The absence of a central strength member (e.g. GRP rod) and outer jacket means the fiber optic assembly  10  has a relatively small cross-sectional area A and cable diameter CD when compared with similar cables having an equivalent fiber count. According to the present embodiments, the bundled unit size of the fiber optic assembly  10  is substantially smaller than, for example, a comparable 12-fiber fan out cable assembly. For example, the fiber optic assembly  10  having twelve subunit fiber optic cables  100  may have a cable diameter CD of about 12.5 mm or less. In another embodiment, the cable diameter CD may be about 11.5 mm or less. By contrast, a comparable conventional riser fan out cable has an average cable diameter of about 13.5 mm. Keeping the size less than 12.7 mm (½ inch) ensures that the fiber optic assembly  10  can be routed through a short section of ½ inch conduit. 
     The fiber optic assembly  10  can be adapted for indoor use, for example, such that an outside cable sheath for the fiber optic assembly is unnecessary. The absence of an outer jacket, as well as omitting a central strength member, in part provides the fiber optic assembly  10  with its relatively low bend diameter. By contrast, in conventional cables, maximum allowable strains on the outer surface of the cable jacket limit the cable bending radius to at least about 5 to 10 times the outer cable diameter. Each subunit cable  100  may be provided with a flexible strength component, such as the layer  158 , so that the fiber optic assembly  10  has sufficient tensile strength while remaining flexible. 
     According to one embodiment of the invention, the bend diameter of the fiber optic assembly  10  having twelve subunit fiber optic cables  100  is less than two inches (50.8 mm) and the tensile strength is at least 100 lbs. According to another embodiment, the bend diameter is less than one inch (25.4 mm), and the tensile strength is at least 200 lbs. According to yet another embodiment, the bend diameter is less than 0.5 inch, and the tensile strength is at least 300 lbs. As shown in  FIG. 5 , the fiber optic assembly  10  can be folded back on itself. 
     According to one embodiment of the invention, the tensile limit for allowable strain on the optical fibers in the fiber optic assembly  10  having twelve subunit fiber optic cables  100  is at least 200 lbs., with the tensile limit for each subunit fiber optic cable  100  being at least 30 lbs. According to another embodiment of the invention, the tensile limit for the fiber optic assembly  10  is at least 300 lbs., with each subunit fiber optic cable  100  having a tensile limit of at least 40 lbs. According to another embodiment of the invention, the tensile limit for the fiber optic assembly  10  is in the range of 300 lbs to 600 lbs, with each subunit fiber optic cable  100  having a tensile limit of at least 50 lbs. 
     EXAMPLE 1 
     A fiber optic assembly  10  as illustrated in  FIGS. 1-2  is formed from twelve flame retardant fiber optic subunit cables  100 . The subunit cables  100  are single fiber cables SZ stranded together. The fiber optic assembly  10  has a minimum bend such that it can be folded back on itself ( FIG. 5 ) and a tensile strength of at least 300 lbs. A pair of outer binders  110 ,  114  made from polyester are contra-helically stranded about the outer layer  130  of nine subunit cables  100 . An inner binder  118  is helically wound about an inner layer  120  of three inner subunit cables  100 . Each subunit cable  100  has a diameter of 2.9 mm. The cable diameter CD is 11.1 mm. The fiber optic assembly  10  has no outer jacket or central strength member. The tensile rating for each subunit fiber optic cable is 50 lbs. The fiber proof stress of the inner three subunit cables  100  is 200 kpsi, and the fiber proof stress for the outer nine subunit cables  100  is 100 kpsi. The higher fiber proof stresses for the inner subunit cables  100  accommodates the higher level of axial strain of the inner subunit cables as compared with the outer subunit cables  100 . 
     One relevant test limit for tensile performance requires the short term fiber strain to be less than 60% of the fiber proof test. Varying the proof test between the inner and outer layers ensures that all twelve fibers will reach their 60% proof test limit at approximately the same time resulting in a high tensile strength rating in the range of 300 to 600 lbs. 
     According to the above-described embodiments, the low bend diameter and small cross-sectional area in part allow the fiber optic assembly  10  to be bent around corners and otherwise introduced into tight spaces or through apertures, while maintaining acceptable attenuation loss performance. The fiber optic assembly  10  is therefore particularly suited for providing fiber optic service indoors to structures such as multiple dwelling units (MDU). In one method of installation, the fiber optic assembly  10  could be placed in a corner molding raceway and single fiber subunit cables  100  can be dropped at each apartment of a MDU. While the subunit cables  100  can be stranded in various ways, SZ stranding provides ease of access at midspan locations of the assembly  10 . 
       FIG. 8  is a perspective view of a portion of a fiber optic assembly  200  or bundled optical cable according to a second embodiment of the invention.  FIG. 9  is a cross-sectional view of the fiber optic assembly  200  taken on line  9 - 9  in  FIG. 8 . The arrangement of the assembly  200  can be generally similar to the cable  10  shown in  FIGS. 1 and 2 . As in the cable  10 , the fiber optic assembly  200  comprises an inner layer  320  of three subunit fiber optic cables  300  surrounded by an outer layer  330  of nine cables  300 . A pair of oppositely helically wound outer or external binders  310 ,  314  are wound about the external periphery of the bundle of subunit cables  300 . The assembly  200  does not, however, include an inner binder around the inner layer  320 . 
     In the illustrated embodiment, the subunit cables  300  are SZ stranded together, with a reversal point generally indicated at  334 . The outer binders  310 ,  314  may be contra-helically stranded about the outer layer  330  of subunit cables  300 . In general, the lay length of the helically wrapped external binders  310 ,  314  is smaller than the lay length of the subunit cables  300 , but other suitable lay lengths are possible. The adjoining inner and outer layers  320 ,  330  of subunit cables  300  can be stranded in separate passes on separate stranders or on a common strander in a single pass. The binders  310 ,  314  can be made from, for example, high strength materials formed from tensile yarns, such as aramid, fiberglass, polyester and other tensile yarns. The subunit fiber optic cables  300  used in the fiber optic assembly  200  can be similar to the subunit cables  100  shown in  FIG. 1 . The subunit cables  200 , however, may have a smaller outside diameter, such as, for example, 2.0 mm, or 1.65 mm. 
     The subunit fiber optic cables  200  can be, for example, flame retardant single fiber cables. In the illustrated embodiment, the subunit fiber optic cables  300  include a single optical fiber  350  surrounded by a buffer coating  354  applied over the optical fiber  350 . The optical fiber  350  may contain a core and a cladding surrounding the core, with one or more polymer coatings applied over the cladding. A layer  358  of loose tensile strength members surrounds the buffer coating  354 , and an outer polymer tubular subunit jacket or sheath  360  is extruded over the layer  358  of strength members. The buffer coating  354  and layer  358  may be formed of materials as discussed above regarding the buffer coating  154  and layer  158 , respectively. The optical fibers  350  used in the subunit fiber optic cables  300  may be bend-insensitive optical fibers such as the ClearCurve™ brand of optical fibers available from Corning Incorporated. The subunit cables  200  of the inner layer  320  may be immediately adjacent and contacting those of the outer layer  330 , with no element being interposed between the layers. 
     The fiber optic assembly  200  having twelve subunit fiber optic cables  300  may have a cable diameter CD, approximated as discussed above for the cable  10 , of about 10 mm or less. In another embodiment, the cable diameter CD may be about 8 mm or less. Small assembly diameter ensures that the fiber optic assembly  200  can be routed through a short section of ½ inch (12.7 mm) conduit. As in the case of the cable  10 , no outside cable sheath or central strength member is required, which in part provides the fiber optic assembly  200  with its relatively low bend diameter D. The layers  358  provide tensile strength to each subunit  300  of at least 120 Newtons maximum short-term tensile load. According to one embodiment, for a subunit outside diameter of 1.65 mm, maximum short-term tensile load is at least 150 Newtons. 
     EXAMPLE 2 
     A fiber optic assembly  200  as illustrated in  FIGS. 8 and 9  is formed from twelve flame retardant fiber optic subunit cables  300 . The subunit cables  300  are single fiber cables SZ stranded together and having ClearCurve™ single mode bend insensitive fibers. A pair of outer binders  310 ,  314  made from polyester are contra-helically stranded about the outer layer  330  of nine subunit cables  300 . Each subunit cable  300  has an outside diameter of 1.65 mm. The average cable diameter CD is about 6 mm. The fiber optic assembly  200  has no outer jacket or central strength member. The maximum short-term tensile load for each subunit fiber optic cable  300  is 150 Newtons. 
       FIG. 10  is a perspective view of a portion of a fiber optic assembly  600  or bundled optical cable according to a third embodiment of the invention.  FIG. 11  is a cross-sectional view of the fiber optic assembly  600  taken on line  11 - 11  in  FIG. 10 . The fiber optic assembly  600  comprises an inner layer  620  of one subunit fiber optic cable  300  surrounded by an outer layer  630  of five cables  300 . A pair of oppositely helically wound outer or external binders  610 ,  614  are wound about the external periphery of the bundle of subunit cables  600 . In the illustrated embodiment, the subunit cables  300  are SZ stranded together, with a reversal point generally indicated at  634 . The outer binders  610 ,  614  may be contra-helically stranded about the outer layer  630  of subunit cables  300 . In general, the lay length of the helically wrapped external binders  610 ,  614  is smaller than the lay length of the subunit cables  300 . The exemplary 1.65 mm outside diameter subunit cables  300  are suitable for use in any of the embodiments described in this specification. 
     The fiber optic assembly  600  having six subunit fiber optic cables  300  may have a cable diameter CD, approximated as discussed above for the cable  10 , of about 6.5 mm or less. In another embodiment, the cable diameter CD may be about 5.5 mm or less. Keeping the size low ensures that the fiber optic assembly  600  can be easily routed through a short section of ½ inch (12.7 mm) conduit. 
     The fiber optic assembly  600  can have a very small bend diameter while maintaining acceptable attenuation losses.  FIG. 12  is a plot of delta attenuation for fibers in selected subunit cables  300  when subjected to a mandrel wrap test at a wavelength of 1550 nm. The mandrel sizes were 10 mm and 15 mm.  FIG. 13  is a plot of delta attenuation for fibers in selected subunit cables  300  when subjected to a corner bend test under various loads at a wavelength of 1550 nm. 
     EXAMPLE 3 
     A fiber optic assembly  600  as illustrated in  FIGS. 10 and 11  is formed from six flame retardant fiber optic subunit cables  300 . The subunit cables  300  are single fiber cables SZ stranded together and having ClearCurve™ single mode bend insensitive fibers. A pair of outer binders  610 ,  614  made from polyester are contra-helically stranded about the outer layer  630  of nine subunit cables  300 . Each subunit cable  300  has a diameter of 1.65 mm. The cable diameter CD is 4.8 mm. The fiber optic assembly  600  has no outer jacket or central strength member. The maximum short-term tensile load for each subunit fiber optic cable  300  is 150 Newtons. 
     Table 1 describes attenuation data for the cable assembly  600  of  FIG. 10 , using ClearCurve™ single mode fiber in the subunit cables  300 , in a mandrel wrap test using a 15 mm diameter mandrel with varying numbers of wraps, at a wavelength of 1550 nanometers. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 15 mm Mandrel Wrap Delta Attenuation at 1550 nanometers 
               
            
           
           
               
               
               
               
            
               
                   
                 Color 
                 Wrap # 
                 delta attenuation (dB) 
               
               
                   
                   
               
               
                   
                 Aqua 
                 1 
                 0.00 
               
               
                   
                 Aqua 
                 2 
                 0.02 
               
               
                   
                 Aqua 
                 3 
                 0.05 
               
               
                   
                 Aqua 
                 4 
                 0.08 
               
               
                   
                 Aqua 
                 5 
                 0.10 
               
               
                   
                 Rose 
                 1 
                 0.01 
               
               
                   
                 Rose 
                 2 
                 0.02 
               
               
                   
                 Rose 
                 3 
                 0.04 
               
               
                   
                 Rose 
                 4 
                 0.03 
               
               
                   
                 Rose 
                 5 
                 0.05 
               
               
                   
                 Red 
                 1 
                 0.03 
               
               
                   
                 Red 
                 2 
                 0.07 
               
               
                   
                 Red 
                 3 
                 0.08 
               
               
                   
                 Red 
                 4 
                 0.11 
               
               
                   
                 Red 
                 5 
                 0.12 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 1, each of the three tested fibers in the subunits of the cable assembly  600  experience an absolute delta attenuation value of less than 0.2 dB at 1550 nm under up to five wraps about the 15 mm mandrel. Each of the three tested fibers experience a delta attenuation of less than 0.2 dB under up to three wraps about the 15 mm mandrel. Each of the three tested fibers experience a delta attenuation of less than 0.15 dB under up to four wraps about the 15 mm mandrel. Each of the three tested fibers experience a delta attenuation of less than 0.10 dB under up to two wraps about the 15 mm mandrel. Each of the three tested fibers experience a delta attenuation of less than 0.05 dB under up to one wrap about the 15 mm mandrel. 
     Table 2 describe attenuation data for cable assembly  600  if  FIG. 11  using ClearCurve™ single mode bend insensitive fiber in the subunit cables  300 , in a mandrel wrap test using a 10 mm diameter mandrel, under varying numbers of wraps, at a wavelength of 1550 nanometers. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 10 mm Mandrel Wrap Delta Attenuation at 1550 nanometers 
               
            
           
           
               
               
               
               
            
               
                   
                 Color 
                 Wrap # 
                 delta attenuation (dB) 
               
               
                   
                   
               
               
                   
                 Aqua 
                 1 
                 0.04 
               
               
                   
                 Aqua 
                 2 
                 0.13 
               
               
                   
                 Aqua 
                 3 
                 0.17 
               
               
                   
                 Aqua 
                 4 
                 0.21 
               
               
                   
                 Aqua 
                 5 
                 0.29 
               
               
                   
                 Rose 
                 1 
                 0.02 
               
               
                   
                 Rose 
                 2 
                 0.08 
               
               
                   
                 Rose 
                 3 
                 0.10 
               
               
                   
                 Rose 
                 4 
                 0.15 
               
               
                   
                 Rose 
                 5 
                 0.16 
               
               
                   
                 Red 
                 1 
                 0.07 
               
               
                   
                 Red 
                 2 
                 0.12 
               
               
                   
                 Red 
                 3 
                 0.23 
               
               
                   
                 Red 
                 4 
                 0.28 
               
               
                   
                 Red 
                 5 
                 0.36 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 2, each of the three tested fibers of the cable assembly  600  experience an absolute delta attenuation value of less than 0.5 db at 1550 nm under up to five wraps about the 10 mm diameter mandrel. Each of the three tested fibers experience an absolute delta attenuation value of less than 0.4 db at 1550 nm under up to three wraps about the 10 mm diameter mandrel. Each of the three tested fibers experience an absolute delta attenuation value of less than 0.3 db at 1550 nm under up to four wraps about the 10 mm diameter mandrel. Each of the three tested fibers experience an absolute delta attenuation value of less than 0.2 db at 1550 nm under up to two wraps about the 10 mm mandrel. Each of the three tested fibers experience an absolute delta attenuation value of less than 0.1 db at 1550 nm under up to one wrap about the 10 mm mandrel. 
     Table 3 describe attenuation data for cable assembly  600  if  FIG. 11  using ClearCurve™ single mode fiber in the subunit cables  300 , in a corner bend test under various loads, at 1550 nanometers. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Corner Bend Delta Attenuation at 1550 nanometers 
               
            
           
           
               
               
               
               
            
               
                   
                 Color 
                 Wgt. (kg) 
                 delta attenuation (dB) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Aqua 
                 2 
                 0.01 
               
               
                   
                 Aqua 
                 6 
                 0.06 
               
               
                   
                 Aqua 
                 10 
                 0.14 
               
               
                   
                 Aqua 
                 14 
                 0.25 
               
               
                   
                 Rose 
                 2 
                 0.03 
               
               
                   
                 Rose 
                 6 
                 0.14 
               
               
                   
                 Rose 
                 10 
                 0.56 
               
               
                   
                 Rose 
                 14 
                 0.61 
               
               
                   
                 Yellow 
                 2 
                 0.04 
               
               
                   
                 Yellow 
                 6 
                 0.18 
               
               
                   
                 Yellow 
                 10 
                 0.21 
               
               
                   
                 Yellow 
                 14 
                 0.18 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 3, each of the three tested fibers of the cable assembly  600  experiences an absolute delta attenuation value of less than 0.6 dB under a load of 10 kilograms at 1550 nm in the corner bend test. Each of the three tested fibers experiences a delta attenuation value of less than 0.3 under a load of 6 kilograms in the corner bend test. Each of the three tested fibers experiences a delta attenuation value of less than 0.1 under a load of two kilograms in the corner bend test. 
     According to one aspect of the present invention, the subunit cables of the fiber optic assemblies can be colored according to industry standard code. The fiber optic assemblies could be placed in a corner molding raceway and single fiber subunit cables can be dropped at each apartment of a MDU. Each individual cable can also have a unique print identifier to facilitate connection to the correct FDT port. For example, at a first living unit of an MDU, the technician can access the subunit cable  300  with “CONN  1 ” printed thereon. The second living unit can receive the white subunit cable  300  with “CONN  2 ” printed thereon, and so on through the sixth subunit labeled “CONN  6 .” The direction of the print can be used to facilitate error-free installation, and can be arranged to as to always point away from (or toward) the FDT. This enables the technician to cut the subunit cable and reliably drop to the proper location. This is an important feature because the technician must typically cut the subunit cable at a point at least six feet past the point where the terminated drop is to be placed. SZ stranding provides ease of access to subunit cables at midspan locations of the fiber optic assemblies. Dual six fiber color coding (e.g. blue through white and black through aqua) can be used in twelve-fiber embodiments to provide two paths exiting the connection closet in MDUs. The lower color fibers (e.g. blue through white), for example, can be routed to lower numbered apartments in one direction and higher color fibers (e.g. black through aqua) can be routed in the opposite direction. Splitting groups of six fibers in this manner reduces the amount of cable needed per floor. 
     According to the above-described embodiments, the low bend diameter and small cross-sectional area in part allow the fiber optic assemblies to be bent around corners and otherwise introduced into tight spaces or through apertures, while maintaining acceptable attenuation loss performance. The fiber optic assemblies are therefore particularly suited for providing fiber optic service indoors to structures such as multiple dwelling units (MDU). 
     The illustrated embodiments show fiber optic cable assemblies having a plurality of single fiber subunit cables. Subunit fiber optic cables having more than one optical fiber, such as two, three or more optical fibers, may also be used in fiber optic cable assembly embodiments constructed according to the principles of the present invention. Further, varying numbers of subunit cables, such as eight, twenty-four, etc., can be arranged into a fiber optic cable assembly according to the present invention. 
     Many modifications and other embodiments within the scope of the claims will be apparent to those skilled in the art. For instance, the concepts of the present invention can be used with any suitable fiber optic cable design and/or method of manufacture. For instance, the embodiments shown can include other suitable cable components such as an armor layer, coupling elements, different cross-sectional shapes, or the like. Thus, it is intended that this invention covers these modifications and embodiments as well those also apparent to those skilled in the art.