Abstract:
A tool and method for accessing fibers within an optical fiber cable is provided. The tool can be used to access optical fibers within buffer tubes held in distribution cables. The tool works well even when the buffer tubes to be accessed are held tightly within distribution cables. In one embodiment, the tool is clamped over a buffer tube and a blade is slid across a blade guide of the tool to facilitate the cutting of a fiber access window in the buffer tube. The method of accessing fibers within a fiber optic cable includes supporting a section of buffer tube and sliding a blade across the mid-portion of the supported section thereby creating optical fiber access windows therein.

Description:
TECHNICAL FIELD 
   The principles disclosed herein relate to a fiber optic cable access tool. 
   BACKGROUND 
   The tool of the present invention is for use on optical fibers. To facilitate the understanding of the invention, an exemplary optical network for delivering high bandwidth communication capabilities to customers is described herein.  FIG. 1  illustrates an exemplary network  100 . As shown in  FIG. 1 , the network  100  is a passive network that includes a central office  110  connected to a number of end subscribers  115  and a larger network such as the Internet (not shown). The network  100  includes fiber distribution hubs (FDHs)  130  having one or more optical splitters that generate a number of individual fibers that lead to the premises of an end user  115 . 
   The portion of network  100  that is closest to central office  110  is commonly referred to as the F 1  region, where F 1  is the “feeder fiber” from the central office. The portion of network  100  that includes a number of end users  115  may be referred to as an F 2  portion of network  100 . Splitters used in an FDH  130  may accept a feeder cable having a number of fibers and may split incoming fibers into, for example, 216 to 432 individual distribution fibers that may be associated with a like number of end user locations. 
   The network  100  includes a plurality of breakout locations  125  at which branch cables (e.g., drop cables, stub cables, etc.) are separated out from main cables (e.g., distribution cables). Breakout locations can also be referred to as tap locations or branch locations and branch cables can also be referred to as breakout cables. Branch cables can manually be separated out from a main cable in the field using field splices. As an alternative to manual splicing in the field, pre-terminated cable systems have been developed. Pre-terminated cable systems include factory integrated breakout locations manufactured at predetermined positions along the length of a main cable (e.g., see U.S. Pat. Nos. 4,961,623; 5,125,060; and 5,210,812). Whether manual field splicing or pre-terminated cable systems are used, cutting the entire distribution cable  220  at each breakout location  125  is undesirable. Preferably only the subsets of the total number of fibers are spliced at each breakout location. Optical fiber accessing tools are used to selectively remove protective and insulating layers around the optical fibers to create a fiber access window in an optical fiber cable. 
   Optical fiber access tools of either the radial slitting or shaver types are typically used to cut a fiber access window in an optical fiber cable. Radial slitters typically include a radially mounted cutting blade for slitting a buffer tube along its length while shaver type tools typically include a cutting blade configured to remove a section of the buffer tube. Exemplary fiber access tools are disclosed in U.S. Pat. No. 4,972,581 to McCollum et al.; U.S. Pat. No. 5,140,751 to Faust; U.S. Pat. No. 5,577,150 to Holder et al.; U.S. Pat. No. 6,023,844 to Hinson, II et al.; U.S. Pat. No. 5,050,302 to Mills; U.S. Pat. No. 4,947,549 to Genovese et al.; U.S. Pat. No. 5,443,536 to Kiritsy et al.; U.S. Pat. No. 5,822,863 to Ott; U.S. Pat. No. 6,581,291 to Tarpill et al.; and U.S. Pat. No. 5,093,992 to Temple, Jr. et al. The tools and methods for accessing optical fibers can be improved. Known fiber access tools are typically difficult to manipulate, especially when the optical fibers to be accessed are tightly wound. In addition, conventional tools tend to bind or chatter, damaging or breaking the buffer tube and the optical fibers contained therein. 
   The present invention addresses the need in the art for an improved access tool and method for access to a limited number of fibers within an optical fiber cable without causing damage to optical fibers within optical fiber cables. 
   SUMMARY 
   The tool and method of the present invention enable an operator to easily and efficiently access optical fibers within an optical fiber cable. According to the invention an improved fiber access tool is provided that secures a buffer tube and provides a blade guide to facilitate the cutting of a fiber access window into a buffer tube. An advantage of the invention is that the tool engages the buffer tube to be cut without substantially displacing the buffer tube from its natural position within the distribution cable. The invention also provides a novel method of creating a fiber access window in a buffer tube. Other advantages will become apparent to those skilled in the art from the following detailed description read in conjunction with the appended claims and drawings attached hereto. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a prior art passive fiber optic network; 
       FIG. 2  is a cross-sectional view of a distribution cable; 
       FIG. 3  shows an example of an initial preparation of the distribution cable at a breakout location of  FIG. 1 ; 
       FIG. 4  is a perspective view of the fiber access tool according to a first embodiment of the invention in a disengaged position; 
       FIG. 5  is a perspective view of the fiber access tool of  FIG. 4  in an engaged position; 
       FIG. 6  is a cross-sectional view of the fiber access tool along line  6 - 6  of  FIG. 5 ; 
       FIG. 7  is a front view of the fiber access tool of  FIG. 5  while the fiber access window is being cut; 
       FIG. 8  is a perspective view of the fiber access tool of  FIG. 4  in an engaged position after the fiber access window has been cut; 
       FIG. 9  is a cross-sectional view of the tool positioned between buffer tubes in a distribution cable; and 
       FIG. 10  is a cross-sectional view of the tool engaging and securing a section of the buffer tube in the distribution cable. 
   

   DETAILED DESCRIPTION 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the embodiments disclosed herein are based. 
   Referring to  FIG. 2 , a typical optical fiber distribution cable  220  includes several buffer tubes  222  twisted in a helix configuration around a central elongate strength or support member  226 , and the resultant structure is surrounded by an outer strength member  228  (e.g., a layer of Kevlar) and a protective jacket  230 . The interior of the buffer tubes  222  is usually filled with a gel which surrounds the individual optical fibers, thereby providing lubrication, water resistance, and a light barrier between optical fibers for preventing interference between the fibers. The distribution cable  220  includes six separate buffer tubes  222  each containing twelve fibers  224 . Ripcords  232  are provided for facilitating tearing away portions of the jacket  230  to access the buffer tubes  222  within the jacket  230 . It should be appreciated that  FIG. 2  depicts but one type of distribution cable; distribution cables can include any number of alternative internal configurations and any number of optical fibers therein. 
   Referring to  FIG. 3 , an exemplary breakout location  125  on the distribution cable  220  is shown. A portion of the outer jacket  230  is first stripped away to provide a stripped region  400  having an upstream end  402  and a downstream end  404 . Portions of the outer strength members  228  can then be removed adjacent the upstream and downstream ends  402 ,  404  so that the buffer tubes  222  are exposed. One of the buffer tubes  222  is then selected and a first window  408  is cut into the buffer tube adjacent the upstream end  402  of the stripped region  400 , and a second window  410  is cut into the buffer tube  222  adjacent the downstream end  404  of the stripped region  400 . The fiber access tool and method of the present invention can be used to cut the windows  408  and  410  in the buffer tube  222 . The fibers  224   dc  desired to be broken out are then accessed and severed at the second window  410 . After the fibers  224   dc  have been severed, the fibers  224   dc  are pulled from the buffer tube  222  through the first window  408  and are ready to be terminated. 
   Referring primarily to  FIGS. 4-6 , an embodiment of the fiber access tool according to principles of the invention is shown. The fiber access tool  10  includes an upper jaw  12  and a lower jaw  14  which are configured to engage a buffer tube  15 . The fiber access tool  10  also includes a first handle member  16  and a second handle member  18  that are connected to the upper and lower jaws  12  and  14 . In the depicted embodiment the handle members  16  and  18  pivot about a pivot axis  19  and are normally biased apart by a spring  20  (see  FIG. 6 ). Normally, the jaws  12  and  14  are closed, but when the handle members are squeezed in together in the direction illustrated by arrows  21  the jaws  12  and  14  open to receive or release the buffer tube  15 . In some embodiments the distance D 1  between the pivot axis  19  and the center axis  13  of the buffer tube  15  is sufficiently large to enable a person to grip a portion of the fiber access tool  10  in front of the pivot axis  19  while cutting into the buffer tube  15  or manipulating the optical fibers within the tube  15 . Gripping the tool in front of the pivot axis can provide auxiliary pressure on the buffer tube  15  via the jaws  12  and  14 . In the depicted embodiment the distance D 1  is between ½ to 3 inches, and more preferably between 1.5 inches. 
   Referring primarily to  FIGS. 4-8 , the jaws  12  and  14  are illustrated and described herein in greater detail. The lower jaw  14  includes a low profile front engagement portion  22  and a rear portion  32 . The rear portion  32  connects the front engagement portion  22  with the second handle member  18 . The front engagement portion  22  in the depicted embodiment includes a top surface  24 , which includes a flat portion  25  and a curved portion  26  (see  FIG. 6 ). The curved portion  26  of the top surface  24  is shaped to contact the outer surface  28  of the buffer tube  15 . The front engagement portion  22  also includes a narrow front surface  30  having a width W 1  and a height H 1 . In some embodiments the height H 1  is about 1/16-¼ inch and the width W 1  is about ½-2 inches. The height H 1  of the front surface  30  is relatively small to enable the tool  10  to engage the buffer tube  15  without pulling the buffer tube  15  away from its original location within the distribution cable. 
   Referring to  FIGS. 9 and 10 , the low profile front engagement portion  22  of the lower jaw  14  can also be referred to as a buffer tube separator, as in the depicted embodiments the low profile front engagement portion  22  is slid between the buffer tube  15  to be accessed and the other buffer tubes  222  in the distribution cable  220 . By rotating the fiber access tool  10 , the selected buffer tube  15  can be pried away from the non-selected buffer tubes  222  so that the upper jaw  12  can conveniently engage the selected buffer tube  15 . 
   Referring back to  FIGS. 4-8 , the upper jaw  12  includes a front engagement portion  34  and a rear portion  36 . The rear portion  36  connects the front engagement portion  34  with the first handle member  16 . The engagement portion  34  includes a top surface  44  and a bottom surface  38 . The bottom surface  38  of the front engagement portion  34  is configured to engage the outer surface  28  of a buffer tube  15 . The bottom surface  38  includes a flat portion  39  and a curved portion  40 . The curved portion  40  of the bottom surface  38  secures the buffer tube  15  against the curved portion  26  of the top surface  24  of the engagement portion  22 . In the depicted embodiment the curved portion  26  defines a groove recess in the bottom surface. It should be appreciated that many other surface profiles are possible. For example, in an alternative embodiment the bottom surface could include one or more teeth-like structures similar to those commonly found on pliers. 
   In the depicted embodiment the combined height of the jaws  12  and  14  is relatively small to enable the fiber access tool  10  to be manipulated in tight spaces. In the depicted embodiment the combined height H 2  of the jaws  12  and  14  in the engaged position is generally between ⅛ to ½ inch. In addition, the distance D 2  (shown in  FIG. 6 ) between the front of the tool  37  and the center axis  13  of the buffer tube  15  is also 1/16 to ½ inch. 
   The engagement portion  34  includes a slot  42  that extends between the top and bottom surfaces  44  and  38  of the engagement portion  34 . The slot  42  is configured to expose a portion of the outer surface  28  of the buffer tube  15  to be cut away to create a fiber access window  46  (see  FIG. 8 ). The slot has a length S that is less than the width W 1  of the front engagement portion  22 . The top surface  44  of the engagement portion  34  is configured to serve as a blade guide to facilitate the blade  48  cutting a cord  50  from the buffer tube  15  without cutting into the optical fibers  52  housed within the buffer tube  15 . In the depicted embodiment the top surface  44  includes a generally U-shaped profile, which controls the path and depth of the cut. More particularly, the top surface  44  includes a first curved transition section  54 , a flat bottom section  56 , and a second curved transition  58 . The transition surfaces  54 ,  58  guide the blade  48  into and out of the buffer tube  15  and the bottom surface  56  guides the blade along the buffer tube  15 . In the depicted embodiment the part of the buffer tube  15  to be cut away protrudes from the slot  42 . The configuration of the slot can be set based upon the thickness and diameter of the buffer tube  15  sheath. The configuration of the slot  42  relative to the transition sections  54  and bottom section  56  can be used to control the depth of the cut D 3  into the buffer tube  15 . Typically the depth D 3  is slightly larger than the thickness of the buffer tube  15 . Referring to  FIG. 7 , the first transition section  54  guides the blade  48  as it breaches buffer tube  15 , cutting a first end of the fiber access window  46 . The bottom section  56  guides the blade  48  as it cuts the body portion of the fiber access window  46 . The second transition section  58  guides the blade  48  as it exits the buffer tube  15  and cuts the second end of the fiber access window  46 . In the depicted embodiment, upper and lower jaws  12  and  14  clamp onto the buffer tube  15  during the cutting step described above. The jaws  12  and  14  prevent the buffer tube  15  from sliding axially away from the blade  48  during the cutting step. The jaws  12  and  14  also prevent the buffer tube from buckling or bulging towards the blade  48  or away from the blade  48  during the cutting step. In other words, the jaws  12  and  14  work in concert with the transition sections  54  and  58  and the bottom section  56  of the tool to help the operator cut a fiber access window  46  in the buffer tube  15 . It should be appreciated that although the fiber access window  46  is shown cut from the right to the left, many other directions are possible. 
   Referring to  FIG. 8 , once the cord  50  of the buffer tube  15  is removed, the optical fibers  52  are exposed and can be accessed. The tool  10  can be used to support the buffer tube  15  while the operator manipulates the optical fibers  52  therein. 
   The first handle portion  16  includes a pair of arms  60  and  62  that extend over and are pivotally connected to the sides of the second handle portion  18 . The handles have a length L measured from the pivot axis  19 . Preferably, the length L is between 1 to 5 inches. In the depicted embodiment the tool is biased closed by the spring  20 , which enables the operator to use both hands to manipulate the fibers or perform the cut as the tool  10 . The spring  20  is shown as a torsion spring positioned near the pivot  19 . It should be appreciated that many other spring arrangements are possible including, for example, a coil compression spring could be used (not shown but well known in the art). 
   From the foregoing detailed description, it will be evident that modifications and variations can be made in the devices of the disclosure without departing from the spirit or scope of the invention. For example, it should be appreciated that the optical fiber access tool according to the invention can be used to cut windows in more than just buffer tubes or optical fiber cables. It can be adapted to cut windows into cylindrical-shaped tubes where it is important to control the depth of the cut.