Patent Publication Number: US-2017371121-A1

Title: Breakout canister for optical trunk cable

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to fiber optic trunk cable. More particularly, the present invention relates to a breakout canister to facilitate breakout of individual data or power cables contained in an optical trunk cable. 
     The ability of high-quality optical fiber to transmit large amounts of information without appreciable signal degradation is well known. As a result, optical fibers have found widespread use in many applications, such as voice and data transmission. For example, optical fiber is often fed up a tower (or to a rooftop) to remote radio units (RRUs) located at the top. In this regard,  FIGS. 1 and 2  illustrate a hybrid power/data trunk cable that can be used for this purpose. As shown, the trunk cable is fed in this example from a baseband unit (BBU) to multiple RRUs located, e.g., on top of a tower. A breakout canister located near the top of tower is used to separate the power or fiber conductors needed for each of the RRUs. 
     Different styles of breakout canisters are known. In this regard,  FIGS. 3 and 4  respectively illustrate a two-piece screw canister and a three-piece c-clip canister. The two-piece screw canister design uses a heat shrink material to seal protruding cable from the nozzle area. Entry of water into the canister is an issue if the heat shrink is not sealed properly around the nozzle and cable jacket. In addition, the heat shrink material is relatively expensive, raising overall costs.  FIG. 5  shows an example of an assembled two-piece screw canister with heat shrink and cable. 
     An example of the three-piece c-clip canister design is shown in  FIGS. 6 and 7 . In this case, corrugated tubes are placed over the cables and nozzles and sealed with epoxy. (This particular application requires corrugated tubes over the fiber cables for protection against birds.) The area where the fiber cable exits the nozzle is sealed with epoxy (for sealing against entry of water) before the corrugated tube is placed over this area. The bottom location where the main trunk cable enters the canister is sealed with heat shrink, as shown in  FIG. 8 . 
     The present invention recognizes the foregoing considerations, and others, of the prior art. 
     SUMMARY OF THE INVENTION 
     According to one aspect, the present invention provides an optical fiber trunk cable breakout canister comprising a main canister portion have a first smaller end and a second larger end, a stop being defined at a predetermined axial distance from the second larger end. A nozzle plate carrying a plurality of axial nozzles is received in the second larger end of the main canister portion such that it engages the stop. A first axial distance between the nozzle plate and ends of the nozzles is lass than a second axial distance between the nozzle plate and the second larger end of the main canister portion. Potting material (e.g., epoxy and/or urethane) is located in the main canister portion so as to cover and seal the nozzle ends. 
     In some embodiments, a cushioning element (e.g., an O-ring gasket) may interpose the stop and nozzle plate such that the nozzle plate engages the stop through the cushioning element. Moreover, the main canister portion may define a groove on an inner surface thereof spaced apart from the stop, the groove receiving a retaining clip such that the nozzle plate is located between the stop and the retaining clip. 
     The main canister portion may be integrally formed having a smaller first tubular portion at which the first smaller end is located, an intermediate conical portion, and a larger second tubular portion at which the second larger end is located. The first smaller end may define a recessed shoulder in which potting material is received. 
     Preferably, the potting material fills an area in the main canister portion having a third axial distance greater than the second axial distance. In many cases, the third axial distance may be less than the second axial distance. 
     Another aspect of the present invention provides an arrangement comprising a breakout canister having a main canister portion with a first end and a second end and a nozzle plate located in the main canister portion. The nozzle plate carries a plurality of nozzles oriented toward the second end of the main canister portion. In this case, the main housing portion and the nozzle plate are configured such that the nozzles are located entirely inside an axial length of the main canister portion. An optical trunk cable having a plurality of subunits contained in an outer jacket is broken out inside of the breakout canister such that the subunits pass through the nozzles. Potting material is located in the main canister portion so as to cover and seal ends of the nozzles. 
     A further aspect of the present invention provides a method of breaking out an optical trunk cable. One step of the method involves providing a breakout canister comprising a main canister portion having a first smaller end and a second larger end, the breakout canister further having a separate nozzle plate carrying a plurality of axial nozzles. According to another step, a portion of an outer jacket of the trunk cable is removed so that subunits in the trunk cable can be separated. The trunk cable is passed through the first smaller end of the main canister portion such that the first smaller end surrounds the outer jacket but the subunits are separate inside the main canister portion. According to another step, the nozzle plate is positioned in the main canister portion such that the nozzles are located entirely inside an axial length of the main canister portion, the subunits passing through the nozzles out the second larger end of the main canister portion. An area inside of the main canister portion between the nozzle plate and the second larger end is filled with a potting material that covers and thus seals ends of the nozzles. 
     Other objects, features and aspects of the present invention are provided by various combinations and subcombinations of the disclosed elements, as well as methods of practicing same, which are discussed in greater detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic representation showing a trunk cable being broken out into three RRUs using a direct breakout canister of the prior art. 
         FIG. 2  is a diagrammatic representation showing more detail regarding the trunk cable used in  FIG. 1 . 
         FIG. 3  shows a two-piece screw canister of the prior art with parts separated. 
         FIG. 4  shows a three-piece C-clip canister of the prior art with parts separated. 
         FIG. 5  shows use of heat shrink tubing with the nozzles of the canister of  FIG. 3 . 
         FIGS. 6-8  show additional detail regarding the use of the canister of  FIG. 4 . 
         FIG. 9  is an exploded view of an improved canister in accordance with the present invention. 
         FIG. 10  is a partial cross-sectional view of the canister of  FIG. 9  with parts assembled. 
         FIG. 11  is a view similar to  FIG. 10  as it would appear in use to break out a trunk cable. 
         FIGS. 12-14  are similar to  FIGS. 9-11 , respectively, but show the addition of an optional annular cushioning element between the nozzle plate and the main canister. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. 
     Referring now to  FIGS. 9-11 , the present invention provides an improved breakout canister which overcomes various considerations of the prior art. In this embodiment, a breakout canister  10  comprises a main canister  12 , a nozzle plate  14 , and a C-clip  16 . Main canister  12  has a hollow interior in which individual cables of the trunk cable are separated. In this regard, the main trunk cable enters an opening at a smaller end  18 . A conical portion  20  increases the diameter of main canister  12  to that of a larger cylindrical portion  22 . Portion  22  defines an open end  24  into which nozzle plate  14  is received. One or more grooves, such as groove  26 , may circumscribe the outer surface of main canister  12  for attachment of mounting clamps and the like. 
     As can be most easily seen in  FIG. 10 , the interior of portion  22  preferably defines a stop  28  which will prevent further insertion of nozzle plate  14 . In other words, nozzle plate  14  is inserted until it is reaches stop  28 . C-clip  16  is then radially compressed and inserted into opening  24  behind nozzle plate  14 . When C-clip  16  reaches a radial groove  30 , it expands so as to lock nozzle plate  14  into place. As shown, groove  30  is spaced apart from stop  28  by an axial distance slightly greater than the width of nozzle plate  14 . Smaller end  18  of main canister  12  preferably defines an interior shoulder  32  for reasons that will be described below. 
     Nozzle plate  14  carries a plurality of cylindrical nozzles  34  through which subunits of separated cables can be routed. This is shown in  FIG. 11 , where subunits  36  of trunk cable  38  are shown separated inside of canister  10  and pass through separate nozzles  34 . As can be seen, nozzles  34  preferably have an axial length L 1  which is less than the axial length L 2  between nozzle plate  14  and the end of portion  22 . As a result, the protruding cable from the nozzles can be potted and sealed with epoxy, urethane, or other suitable potting material, as shown at  40 . Because the potting material covers the ends of nozzles  34 , no heat shrink is required to seal these areas. While the potting material is not flush with the end of portion  22  in this example, one skilled in the art will recognize that flush potting may be desirable in some applications. 
     The opening through which trunk cable  38  is received may also be sealed without use of heat shrink material in this embodiment. Specifically, as indicated at  42 , epoxy or other suitable potting material may be located in shoulder  32  to effectively seal this interface. 
     Referring now to  FIGS. 12-14 , an alternative embodiment is illustrated. In this case, an optional annular cushioning element  50  is provided between nozzle plate  14  and main canister  12 . For example, the cushioning element  50  may be any suitable gasket, or solid or hollow O-ring, formed of an appropriate resilient material. In this embodiment, element  50  is captured between the back face of nozzle plate  14  and stop  28  when the components are assembled. As shown in  FIGS. 13-14 , element  50  preferably compresses as nozzle plate  14  is moved into position and retained via C-clip  16 . 
     Alternatively, embodiments are contemplated in which plate  14  is retained by potting material, such as potting material  40  of  FIG. 11 , without the use of a C-clip  16 . Moreover, embodiments are contemplated in which stop  28  is provided by a C-clip or the like on the portion  22  side of the plate  14 . Furthermore, stop  28  may be omitted in some embodiments, such as embodiments that utilize potting material  40 . 
     It can thus be seen that the present invention provides an improved fiber cable breakout canister. While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art without departing from the spirit and scope of the present invention. Furthermore, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention as further described in the appended claims.