Patent Publication Number: US-2013236141-A1

Title: Optical cable connection closure

Description:
RELATED APPLICATIONS 
     This application claims priority from Japanese Application No. 2012-053080, filed Mar. 9, 2012, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an optical cable connection closure. 
     2. Related Art 
     Conventionally, in the construction of a fiber-to-the-home (FTTH) network, an optical cable may be split off from a cable in an overhead line system and the optical cable is then drawn into a residence and the like. An optical cable connection closure is widely used as the location at which the optical cable is split off from the overhead line system cable. A known example of such art, as disclosed, for example, in patent document 1, is an optical fiber distribution box allowing for an optical fiber (branching optical cable) to be split off from an overhead optical drop cable (trunk optical cable) and drawn into a residence and the like. 
     The optical fiber distribution box disclosed in Japanese Unexamined Patent Application Publication No. 2006-53261 (Patent Document 1) is provided with a housing (closure body) having a housing space for housing optical fibers and the like and a plate-shaped piece for suspending the housing from a support line of the optical drop cable. The housing is provided with an optical fiber housing space arranged in the center of the housing, and a retaining piece for retaining an optical connection arranged so as to sandwich the optical fiber housing space along the direction of suspension. 
     SUMMARY 
     The optical cable, messenger wire, and the like of a cable group of an overhead line system are generally bundled together by a spiral-shaped spiral hanger. Thus, an optical cable connection closure (hereafter, also referred to as simply “closure”) is normally suspended from the messenger wire, and installed near the residence into which the optical cable is to be drawn. When an optical cable connection closure is installed near a residence in this way, it is desirable to reduce the size of the closure and make it less conspicuous, thereby ensuring the esthetic appeal of the closure. 
     However, in the conventional optical fiber distribution box described above, the dimensions, for example, of the suspension direction may be large, making the housing suspended from the messenger wire conspicuous. Therefore, there is the risk of the esthetic appeal of the optical cable connection closure being reduced. Thus, there has been a demand in recent years for an optical cable connection closure that can be made less conspicuous when suspended from a messenger wire, allowing for improved esthetic appeal. 
     The present invention was contrived in light of the circumstances described above, and an object of the present invention is to provide an optical cable connection closure that can improve the esthetic appeal. 
     The present invention is an optical cable connection closure having at least first and second mutually separable optical cables, the closure housing a trunk optical cable extending in a predetermined direction and optically connecting a branching optical cable to the second optical cable via an optical connector. The optical cable connection closure is suspended from a wire for supporting the trunk optical cable, and is provided with a rigid closure body capable of supporting the trunk optical cable, branching optical cable, and optical connector. The closure body has a first layer for housing the trunk optical cable, a second layer for housing the separated second optical cable, and a third layer for housing the optical connector, the first through the third layers being layered in that order in a direction perpendicular to the direction in which the closure body is suspended and the predetermined direction, and at least a part thereof overlapping as seen from the perpendicular direction. 
     In the optical cable connection closure, the first layer that houses the trunk optical cable, the second layer that houses the second optical cable, and the third layer that houses the optical connector are layered in the perpendicular direction. The first through the third layers are arranged so that at least parts thereof overlap one another as seen from the perpendicular direction. Such a configuration allows the dimensions of the closure body in the suspension direction to be reduced, and the closure body to be made more compact. It is thereby possible to make the closure body suspended from the wire inconspicuous, and to improve the esthetic appeal of the optical cable connection closure suspended from the wire. 
     The closure body also preferably has a fourth layer for housing the branching optical cable, this fourth layer being included within either the second or the third layer. This allows for favorable housing of the branching optical cable and for the closure body to be made more compact. 
     A specific example of a configuration favorably yielding the effects described above is one in which the closure body is formed in a box shape with a first shell and a second shell abutting each other in the perpendicular direction, the first layer being provided within the first shell, and the third layer being provided within the second shell. 
     Another specific example of a configuration favorably yielding the effects described above is one in which the closure body is formed with a frame extending in a predetermined direction so as to delineate first and second housing sections, the first layer being provided within the first housing section, and the third layer being provided within the second housing section. 
     A plurality of catches for retaining the second optical cable in a state wrapped in the circumferential direction around the axis of the perpendicular direction is preferably provided within the second layer, a part of the plurality of catches catching the second optical cable so as to be movable with respect to the circumferential direction. This allows the second optical cable to be efficiently housed within the second layer regardless of the length of the separated second optical cable. 
     In accordance with the present invention, it is possible to provide an optical cable connection closure that enables improved esthetic appeal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the configuration of an overhead line system from which an optical cable connection closure according to a first embodiment is suspended. 
         FIG. 2  is a cross-sectional schematic view of the structure of a trunk optical cable. 
         FIG. 3  is a frontal view of a cover of the optical cable connection closure according to the first embodiment in an open state. 
         FIG. 4  is a right side view of the optical cable connection closure according to the first embodiment. 
         FIG. 5  is a perspective view of a case and a cover. 
         FIG. 6  is a magnified perspective view of part of the case and the cover. 
         FIG. 7  is a perspective view of a hanger. 
         FIG. 8  is a left side view of a first manner of attaching the hanger. 
         FIG. 9  is a left side view of a second manner of attaching the hanger. 
         FIG. 10  is an illustration that describes an operation of splitting an optical cable using the optical cable connection closure according to the first embodiment. 
         FIG. 11  is an illustration that describes a step of splitting a second optical cable of a single trunk optical cable. 
         FIG. 12  is an illustration that describes a step of connecting the second optical cable and a branching optical cable using an optical connector. 
         FIG. 13  is an illustration that describes a step of housing the second optical cable, the optical connector, and the branching optical cable within a closure body. 
         FIG. 14  is an illustration of another trunk optical cable in a split state. 
         FIG. 15  is a perspective illustration that describes an optical cable connection closure according to a second embodiment. 
         FIG. 16  is another perspective illustration that describes the optical cable connection closure according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of an optical cable connection closure according to the present invention will be described in detail below with reference to the accompanying drawings. In the following descriptions, identical or similar parts are assigned the same reference number, and any redundant description thereof will be omitted. The terms “inner” and “outer” correspond to the inner and outer sides of the optical cable connection closure. The X, Y, and Z directions are based on the state shown in the drawings, and are for convenience. 
     First Embodiment 
     The optical cable connection closure according to the present embodiment is used, for example, at a location at which an optical cable is split off from a cable of an overhead line system forming part of an FTTH network. First, the overhead line system will be described. As shown in  FIG. 1 , an overhead line system  100  extending in a predetermined direction (X direction) is provided with a cable group, a messenger wire  3 , and a spiral hanger  4 . The cable group includes, for example, trunk optical cables  5 A to  5 D and another optical fiber cable  6 . The messenger wire  3  works with the spiral hanger  4  to retain the cable group. The spiral hanger  4  extends in a spiral along the X direction, and bundles together the cable group and the messenger wire  3 . 
     A description of the trunk optical cables  5 A to  5 D follows. In the present embodiment, the four trunk optical cables  5 A to  5 D extend along the messenger wire  3 . The trunk optical cables  5 A to  5 D all share the same configuration. Thus, the following description will feature trunk optical cable  5 A by way of example. 
     As shown in  FIG. 2 , the trunk optical cable  5 A is provided with a tension wire  5   t , a first optical cable  5   f , and a second optical cable  5   s . The tension wire  5   t , first optical cable  5   f , and second optical cable  5   s  are coupled together in that order. 
     The tension wire  5   t , which has a circular cross section, is a metal member for receiving tension acting upon the first and second optical cables  5   f  and  5   s . The first optical cable  5   f  has an optical fiber  5   p  having a circular cross section, and an outer sheath  5   g  having a rectangular cross section covering the optical fiber  5   p . The optical fiber  5   p  is arranged in a position roughly in the center of the cross section of the outer sheath  5   g . While not shown in the drawings, the optical cable  5   f  may also be provided with one or more FRP or metal reinforcing members parallel to the optical fiber  5   p . The second optical cable  5   s  provided alongside the first optical cable  5   f  has a configuration similar to that of the first optical cable  5   f.    
     The first optical cable  5   f  and the second optical cable  5   s  are connected by a coupler  5   j  in a manner that allows them to be separated, and the first optical cable  5   f  and second optical cable  5   s  can be cut apart, as necessary, starting at the coupler  5   j.    
     Next, an optical cable connection closure  1  will be described. As shown in  FIG. 3 , the optical cable connection closure  1  houses at least part of the trunk optical cables  5 A to  5 D, and optically connects via optical connectors  8 A to  8 D the branching optical cables  7 A to  7 D to the single-core second optical cable  5   s  split off therefrom. 
     The branching optical cables  7 A to  7 D are connected to the second optical cable (excess cable length)  5   s , and are used to extend into a residence. The optical connectors  8 A to  8 D have long rectangular shapes. The optical connectors  8 A to  8 D optically connect the respective second optical cables  5   s  of the trunk optical cables  5 A to  5 D and the branching optical cables  7 A to  7 D so that the two abut each other in the lengthwise direction thereof. 
     The optical cable connection closure  1  is provided with a closure body  10  for housing the trunk optical cables  5 A to  5 D and a hanger  50  for suspending the closure body  10  from the messenger wire  3 . The closure body  10  of the optical cable connection closure  1  is perpendicularly suspended facing downward in a suspension direction (Z direction) from the messenger wire  3  via the hanger  50 . 
     As shown in  FIGS. 3 to 6 , the closure body  10  is rigid enough to be capable of supporting the trunk optical cables  5 A to  5 D, the branching optical cables  7 A to  7 D, and the optical connectors  8 A to  8 D, and forms, for example, the skeleton of the optical cable connection closure  1 . The closure body  10  in the present discussion is made of plastic. The rigidity of the closure body  10  can be set using, for example, the strength of the plastic forming the closure body  10 , the shape (dimensions) thereof, and the like. 
     The closure body  10  has a base  11  constituting a first shell, and a cover  12  constituting a second shell. The base  11  and the cover  12  are coupled by a hinge  13  so as to be rotatable with respect to each other around an axis of rotation following the X direction. The cover  12  is thereby opened and closed with respect to the base  11 . When the base  11  and the cover  12  are in a state of closure (“closed state”) in which the two abut each other in the perpendicular direction (Y direction) perpendicular to the X direction and the Z direction, the closure body  10  forms a box shape that is long with respect to the X direction (see  FIG. 4 ) 
     The base  11  houses the trunk optical cables  5 A to  5 D and the second optical cable  5   s  separated from the first optical cable  5   f . The base  11  has a first layer  14  for housing the trunk optical cables  5 A to  5 D and a second layer  15  for housing the second optical cable  5   s  (see  FIG. 4 ). The first and second layers  14  and  15  each extend in the X direction. 
     As shown in  FIG. 5 , the shell-shaped base  11  consists of a plate-shaped base floor portion  16  and side walls  17   a  to  17   d  rising from the periphery of the base floor portion  16 . Hinges  13  are provided at positions near both ends and roughly in the center of the side wall  17   c , which is perpendicular to the Z direction. A projection  18  for engaging with the cover  12  when the base  11  and the cover  12  are in the closed state and for fixing the cover  12  to the base  11  is provided on the side wall  17   a , which is on the side opposite to the side wall  17   c.    
     The first layer  14  (see  FIG. 4 ) is an area established at the base floor portion  16  within the base  11  and has the X direction as its lengthwise direction. The first layer  14  consists of a pair of rubber seals  19  located near both ends of the base  11 . The rubber seals  19  are provided with four grooves extending in the X direction, the grooves retaining the trunk optical cables  5 A to  5 D. Each of the pair of rubber seals  19  are arranged at positions located at a predetermined distance inward away from the side walls  17   b  and  17   d , which are perpendicular to the X direction. 
     As described above, the first layer  14  contains the rubber seals  19  provided on the base  11 . In other words, the closure body  10  of the present embodiment need not be a separate piece from the base  11 , and the base  11  itself serves to house the trunk optical cables  5 A to  5 D. 
     The second layer  15  (see  FIG. 4 ) is an area established at the inside of the first layer  14  with respect to the Y direction (the side opposite the base floor portion  16 ) in the base  11 , and has the X direction as its lengthwise direction. In other words, the first layer  14  and the second layer  15  are layered in the Y direction so as to be in the same position in the Z direction. As shown in  FIG. 6 , the second layer  15  contains first catches  22  and  23  and second catches  24  and  25  constituting a plurality of catches. The catches  22  to  25  retain the second optical cable  5   s  in a state wrapped along the circumferential direction around an axis extending in the Y direction. 
     As shown in  FIG. 6 , the first catches  22  are vertical pieces rising from the base floor portion  16 , and have a rectangular plate shape having a surface perpendicular to the Z direction. Hooks  22   h  are provided on the inner ends (apical ends) of the first catches  22 . The hooks  22   h  delineate a space  22   j  for retaining the second optical cable  5   s . At the hooks  22   h , the second optical cable  5   s  is guided into the space  22   j  through a gap  22   c  externally linking the space  22   j . The hooks  22   h  are formed so as to be positioned further to the inside with respect to the Y direction than the trunk optical cables  5 A to  5 D retained by the rubber seals  19 . A first catch  22  is arranged in each of the four corners of the second layer  15 . 
     The first catches  23  are vertical pieces rising from the base floor portion  16 , and have a rectangular plate shape having a surface perpendicular to the Z direction. Two hooks  23   h  are provided along the X direction on the inner ends of the first catches  23 . The hooks  23   h  are configured similarly to the hooks  22   h  of the first catch  22  described above. Two first catches  23  are provided on the base  11 . Specifically, the first catches  23  are located at positions roughly in the center of the base  11  with respect to the X direction near the side wall  17   a  and near the side wall  17   c.    
     The second catches  24  are vertical pieces rising from the base floor portion  16  and have a rectangular plate shape having a surface perpendicular to the Z direction. The second catches  24  are located at positions near the side wall  17   a  and the side wall  17   c  and between the first catches  22  and  23 . The second catches  25  are vertical pieces rising from the base floor portion  16  and have a rectangular plate shape having a surface perpendicular to the X direction. The second catches  25  are located between the plurality of second catches  24  with respect to the X direction. 
     The second catches  24  and  25  are preferably arranged so as to overlap as seen from the X direction. This allows the second optical cable  5   s  to be easily threaded between the second catches  24  and  25  when the second optical cable  5   s  is wrapped around the catches  22  to  25 , and for the second optical cable  5   s  to be retained while ensuring a constant radius that is equal to or greater than an acceptable bend radius. The second catches  24  and  25  are capable of reliable retention without placing stress upon the second optical cable  5   s.    
     As discussed above, the second layer  15  contains the first catches  22  and  23  and the second catches  24  and  25  provided on the base  11 . In other words, the closure body  10  need not be a separate piece from the base  11 , and the base  11  itself serves to house the second optical cable  5   s.    
     As shown in  FIG. 3 , the cover  12  houses the optical connectors  8 A to  8 D and the branching optical cables  7 A to  7 D. Specifically, as shown in  FIG. 4 , the cover  12  has a third layer  28  for housing the optical connectors  8 A to  8 D and a fourth layer  29  for housing the branching optical cables  7 A to  7 D. 
     As shown in  FIG. 5 , the shell-shaped cover  12  contains a plate-shaped cover floor portion  31  and side walls  32   a  to  32   d  that rise from the periphery of the cover floor portion  31 . A hinge  13  is provided on the side wall  32   a , which is perpendicular to the Z direction when the base  11  and the cover  12  are in an opened state (“open state”). A locking part  33  is provided on the side wall  32   c  opposite the side wall  32   a  at a position corresponding to that of the projection  18  of the base  11 . The locking part  33  engages with the projection  18  of the base  11  in the closed state, securing the cover  12  to the base  11 . This configuration of the cover  12  allows a sealed space for housing the first through fourth layers  14 ,  15 ,  28 , and  29  to be delineated in a manner that allows opening and closing. 
     The third layer  28  (see  FIG. 4 ) is an area established within the cover  12 . The third layer  28  contains clamps  34  established along the X direction. Each of the clamps  34  has vertical pieces  36   a  and  36   b  rising from the cover floor portion  31 . The interval between the vertical pieces  36   a  and  36   b  in the X direction is roughly the same length as the length of the optical connectors  8 A to  8 D in the lengthwise direction. This enables the optical connectors  8 A to  8 D to be clamped between the vertical pieces  36   a  and  36   b , and as a result, the optical connectors  8 A to  8 D can be attached to the cover  12 . 
     As discussed above, the third layer  28  contains the clamps  34  provided on the cover  12 . In other words, the closure body  10  need not be a separate piece from the cover  12 , and the cover  12  itself serves to house the optical connectors  8 A to  8 D. In the closed state, the third layer  28  is set so as to overlap the first and second layers  14  and  15  as seen from the Y direction, and the first through the third layers  14 ,  15 , and  28  are each layered in the Y direction. 
     The fourth layer  29  (see  FIG. 4 ) is an area included in the third layer  28 . The fourth layer  29  is constituted by the area outside the area in which the optical connectors  8 A to  8 D are positioned within the cover  12 . In other words, the closure body  10  need not be a separate piece from the cover  12 , and the cover  12  itself serves to house the branching optical cables  7 A to  7 D. 
     A retaining piece  38  for retaining the branching optical cables  7 A to  7 D and guiding them outside the closure body  10  is provided on the side walls  32   b  and  32   d  of the cover  12  (see  FIG. 3 ). The retaining piece  38  is provided with four rubber seals  39  located on the side wall  32   b  towards an end  12   e  of the cover  12 , and with four rubber seals  39  located on the side wall  32   d  toward another end  12   f  of the cover  12 . This configuration yields a cover  12  in which eight outlets for leading the branching optical cables  7 A to  7 D to the outside of the closure body  10  are provided. 
     Next, the hanger  50  will be described. As shown in  FIG. 7 , the hanger  50  is for suspending the closure body  10  from the messenger wire  3 . The hanger  50  is provided with a base plate  51  and a grip plate  52 . The base plate  51  has a base  53  extending in the Y direction, and an anchor  54  extending downwards (on one side in the Z direction) from an end  52   a  of the base  53 . The base plate  51  is integrally formed from a single bent plate. 
     The base  53  is provided with a groove  56  that opens upward (on the other side in the Z direction) and extends in the X direction in order to locate the messenger wire  3 . An end  52   b  of the base  53  on the side opposite the end  52   a  is formed as it is bent upward with respect to the base  53  so as to extend in the Z direction. A through-hole  53   c  into which the grip plate  52  is inserted is provided in the end  52   b . The through-hole  53   c  is a rectangular hole penetrating in the Y direction. 
     The anchor  54  has a first part  54   a  extending in the Z direction, a second part  54   b  located nearer the other end  52   b  of the base  53  than the first part  54   a  and extending in the Z direction, and a third part  54   c  that connects the first part  54   a  and second part  54   b . The second part  54   b  is positioned between the end  52   a  and the groove  56  as seen from the Z direction. In other words, as shown in the drawing, the second part  54   b  is located not directly underneath the messenger wire  3 , but rather in a position offset from the messenger wire  3  in the Y direction. An anchor  54   d  for securing the hanger  50  to the base  11  is provided on the second part  54   b . The anchor  54   d  engages with a claw (not shown) provided on the base  11 , coupling the hanger  50  to the base  11 . 
     The grip plate  52  is a plate-shaped member that extends in the Y direction. One end of the grip plate  52  is inserted into the through-hole  53   c  provided in the base plate  51 , and the other end is secured to the base  53  by a bolt  57 . The grip plate  52  is arranged so as to close off part of the groove  56 , thereby working with the base  53  to grip the messenger wire  3  located in the groove  56 . 
     The hanger  50  can be secured to the base  11  by changing the orientation of the hanger  50  (that is, the positional relationship of the ends  52   a  and  52   b  of the base plate  51 ). For example, as shown in  FIG. 8 , the hanger  50  can be secured to the base  11  so that the end  52   a  is positioned towards the cover  12  (that is, so that the end  52   b  is positioned towards the base  11 ). Such a configuration reduces the distance between the closure body  10  and the messenger wire  3  in the Y direction. This causes the closure body  10  to be situated within the spiral constituted by the spiral hanger  4 . It is thereby possible to make the optical cable connection closure  1  inconspicuous, and to improve the esthetic appeal of the optical cable connection closure  1 . 
     On the other hand, as shown in  FIG. 9 , the hanger  50  can be secured to the base  11  so that the end  52   a  is positioned towards the base  11  (that is, so that the end  52   b  is positioned towards the cover  12 ). Such a configuration increases the distance between the closure body  10  and the messenger wire  3  in the Y direction. As opposed to the configuration shown in  FIG. 8 , this enables a space S formed between the closure body  10  and the spiral hanger  4  to be expanded, thereby allowing many cables to be inserted into (housed within) the space S. 
     Next, a method of connecting the branching optical cables  7 A to  7 D to the second optical cables  5   s  of the trunk optical cables  5 A to  5 D using the optical cable connection closure  1  will be described. 
     Step 1 
     First, as shown in  FIG. 10 , the trunk optical cables  5 A to  5 D are housed within the first layer  14  (see  FIG. 4 ) with the cover  12  of the closure body  10  in an open state. Specifically, the trunk optical cables  5 A to  5 D are arranged within the base  11  so as to extend along the X direction, and are inserted into the grooves in the rubber seals  19  so as to form roughly equidistant rows in the Z direction. 
     Step 2 
     Next, as shown in  FIG. 11 , only the second optical cable  5   s  included in the trunk optical cable  5 A is cut, and the second optical cable  5   s  is separated from the first optical cable  5   f  along the coupler  5   j  (see  FIG. 2 ). 
     Step 3 
     Next, as shown in  FIG. 12 , the second optical cable  5   s  and the branching optical cable  7 A are optically connected using the optical connector  8 A. A known optical connector can be used as the optical connector  8 A. 
     Step 4 
     Next, as shown in  FIG. 13 , the second optical cable  5   s  is housed in the second layer  15  (see  FIG. 4 ), and the second optical cable  5   s  is retained in a wrapped-around state. In other words, the second optical cable  5   s  is hung on the first through fourth catches  22  to  25  as the second optical cable  5   s  is being wrapped around in the circumferential direction around an axis in the Y direction. 
     At this time, the second optical cable  5   s  is inserted through the gap  22   c  into the spaces  22   j  and  23   j  of the first catches  22  and  23  (see  FIG. 6 ), and the second optical cable  5   s  is inserted so as to be threaded between the second catches  24  and  25 . The second optical cable  5   s  is thereby held in place so as to be movable in the circumferential direction around an axis in the Y direction. 
     As described above, the first catches  22  and  23  and second catches  24  and  25  for retaining the second optical cable  5   s  wrapped in the circumferential direction around the Y direction are provided within the second layer  15 . These catches  22  to  25  allow the second optical cable  5   s  to be held in place so as to be movable in the circumferential direction. It is thereby possible to house the second optical cable  5   s  within the second layer  15  regardless of the length of the second optical cable  5   s . In this case, the need to precisely set the length of the second optical cables  5   s  separated from the trunk optical cables  5 A to  5 D can be reduced, and the second optical cables  5   s  can be retained without removing the optical connectors  8 A to  8 D and without applying stress thereto even if the lengths of the second optical cables  5   s  vary. As a result, the ease of housing the trunk optical cables  5 A to  5 D within the optical cable connection closure  1  can be further improved. 
     Next, the optical connector  8 A is retained by the clamps  34  of the cover  12 , and as a result, the optical connector  8 A is housed in the third layer  28  (see  FIG. 4 ) established within the cover  12 . Concurrently, the branching optical cable  7 A extending from the optical connector  8 A is housed within the fourth layer  29  (see  FIG. 4 ) of the cover  12 . Specifically, the branching optical cable  7 A is guided through the gap between the clamps  34  and the side wall  32   a  to the end  12   e  of the cover  12 . The branching optical cable  7 A is then guided to the outside of the cover  12  along the X direction through the rubber seals  39  by the end  12   e.    
     Through the steps 1 through 4 described above, the trunk optical cable  5 A is split into the first optical cable  5   f  extending along the messenger wire  3  and the branching optical cable  7 A extended into a residence or the like. Next, as shown in  FIG. 14 , the steps 1 through 4 described above are performed on the other trunk optical cables  5 B to  5 D, thereby likewise splitting the trunk optical cables  5 B to  5 D into first optical cables  5   f  and branching optical cables  7 B to  7 D. When the process of splitting the trunk optical cables  5 B to  5 D has been completed, the cover  12  is closed, and the work is complete. 
     In the present embodiment, the hanger  50  may be attached to the base  11  in advance, or attached to the base  11  after the base  11  and the cover  12  have been closed. In the present embodiment, all of the trunk optical cables  5 A to  5 D were operated upon, but it is also acceptable to operate upon as few as one of the cables as necessary. In the present embodiment, an example in which the trunk optical cable  5 B is split after the trunk optical cable  5 A has been split is discussed, but the order in which the cables are split can be selected as desired. 
     As described above, the branching optical cables  7 A to  7 D guided from the closure body  10  can be removed from the retaining piece  38  near the end  12   e  of the cover  12  without changing the positioning (moving) of the optical connectors  8 A to  8 D, and can also be removed from the retaining piece  38  near the other end  12   f.    
     As discussed above, the first layer  14 , second layer  15 , and third layer  28  of the optical cable connection closure  1  according to the present embodiment are layered in the Y direction. The first through third layers  14 ,  15 , and  28  are arranged so as to overlap each other as seen from the Y direction. Such a configuration allows the dimensions of the closure body  10  in the Z direction to be reduced, and the closure body  10  to be made more compact (miniaturized). It is thereby possible to make the closure body  10  suspended from the messenger wire  3  inconspicuous, and to improve the esthetic appeal of the optical cable connection closure  1  suspended from the messenger wire  3 . 
     As described above, the closure body  10  also has the fourth layer  29  for housing the branching optical cables  7 A to  7 D, the fourth layer  29  being contained within the third layer  28 . This allows the branching optical cables  7 A to  7 D to be housed without increasing the dimensions of the cover  12  in the Y direction or the Z direction, and the closure body  10  to be made more compact. 
     As described above, the base  11  and the cover  12  are linked by the hinges  13  in a manner that allows opening and closing. Such a configuration allows for easy access to the first through fourth layers  14 ,  15 ,  28 , and  29  by opening the cover  12  off of the base  11 . This reduces the need to provide a tray or the like in which to arrange the trunk optical cables  5 A to  5 D and the like on the base  11  or the cover  12 , and enables a more compact design for the closure body  10 . 
     As described above, when suspending the closure body  10  from the messenger wire  3 , the orientation of the hanger  50  with respect to the base  11  can be changed. As a result, either an effect of improving the esthetic appeal of the closure body  10  or an effect of ensuring a space S for housing the cables can be selectively obtained. 
     As described above, the closure body  10  is formed in a box shape such that the base  11  constituting the first shell and the cover  12  constituting the second shell abut each other in the Y direction. As a result, the first through fourth layers  14 ,  15 ,  28 , and  29  are arranged within the closure body  10 , in which a sealed box-shaped area has been delineated. It is thus possible to protect the trunk optical cables  5 A to  5 D, second optical cables  5   s , optical connectors  8 A to  8 D, and branching optical cables  7 A to  7 D housed within the closure body  10  from inclement weather, sunlight, and the like. 
     Second Embodiment 
     Next, an optical cable connection closure according to a second embodiment will be described. The description of the present embodiment will focus on those points differing from the first embodiment described above. 
     As shown in  FIG. 15  and  FIG. 16 , an optical cable connection closure  60  according to the present embodiment differs from the optical cable connection closure  1  described above in that it is provided with a closure body  61  in lieu of the closure body  10  (see  FIG. 1 ). The closure body  61  contains a frame  64 . 
     The frame  64  constitutes the closure body  61 . The frame  64  extends in the X direction, and delineates a first housing section  62  and a second housing section  63  lined up in the Y direction. First and second layers  66   a  and  66   b  are provided within the first housing section  62 , and a third layer  67  is provided within the second housing section  63 . 
     Specifically, the frame  64  contains a plate-shaped rib  68  perpendicular to the Y direction, a pair of flanges  69  provided on both ends of the rib  68  in the Z direction, and a plate-shaped side plate  72  perpendicular to the X direction. The frame  64  is made, for example, of plastic, and is rigid enough to support the trunk optical cables  5 A to  5 D, branching optical cables  7 A to  7 D, and optical connectors  8 A to  8 D. 
     A flange  69   a  on one side in the Z direction (the upper side in the drawing) has a planar shape. The base  53  of the hanger  50  (see  FIG. 7 ) is secured to the flange  69   a . A flange  69   b  on the other side in the Z direction (the lower side in the drawing) has a planar shape with a partial cutout therein. Specifically, as shown in  FIG. 15 , the flange  69   b  on one side of the rib  68  in the Y direction (the front side in the drawing) is only provided at both ends in the X direction, with an opening  70  being formed therebetween. The side plate  72  is provided on both ends of the rib  68  in the X direction so as to bridge the area between the pair of flanges  69 . 
     In such a frame  64 , as shown in  FIG. 15  and  FIG. 16 , two areas that are long with respect to the X direction are separated by the rib  68 , the flanges  69 , and the side plate  72 , one of the areas on one side in the Y direction constituting the second housing section  63 , and the area on the other side in the Y direction constituting the first housing section  62 . A plurality of slits  77  extending in the X direction through which the optical cables  5   s  are inserted is formed at the parts of the rib  68  corresponding to the opening  70 . These slits  77  allow for the second optical cables  5   s  to pass between the second and third layers  66   b  and  67  (that is, between the first and second housing sections  62  and  63 ). 
     A first layer  66   a  is an area established in the first housing section  62  and has the X direction as its lengthwise direction. The first layer  66   a  houses the trunk optical cables  5 A to  5 D. The first layer  66   a  contains a rubber mount  73  positioned in a groove provided in the side plate  72 . The rubber mount  73  houses the trunk optical cables  5 A to  5 D. The frame  64  of the closure body  61  thereby serves on its own to house the trunk optical cables  5 A to  5 D without the need for a part separate from the frame  64 . 
     A second layer  66   b  is an area established further inside than the first layer  66   a  (that is, towards the rib  68 ) within the first housing section  62 , and has the X direction as its lengthwise direction. In other words, the second layer  66   b  is layered in the Y direction so as to occupy the same position as the first layer  66   a  with respect to the Z direction. The second layer  66   b  houses the split second optical cables  5   s.    
     The third layer  67  is an area established inside the second housing section  63 , and has the X direction as its lengthwise direction. In other words, the third layer  67  is layered in the Y direction so as to occupy the same direction as the first and second layers  66   a  and  66   b  with respect to the Z direction. The third layer  67  houses the optical connectors  8 A to  8 D.  FIG. 15  shows the optical connectors  8 A and  8 B in a housed state. 
     The third layer  67  contains a plurality of clamps  74  for housing the optical connectors  8 A to  8 D. The clamps  74  are vertical pieces rising off of the rib  68 , and clamp and secure the optical connectors  8 A to  8 D in the X direction and the Y direction. The frame  64  of the closure body  61  thereby serves on its own to house the optical connectors  8 A to  8 D without the need for a part separate from the frame  64 . 
     A fourth layer  76  is provided within the third layer  67 , and contains a rubber mount  78  positioned within a groove provided on the side plate  72 . The rubber mount  78  retains the branching optical cables  7 A to  7 D. The frame  64  of the closure body  61  thereby serves on its own to house the branching optical cables  7 A to  7 D without the need for a part separate from the frame  64 . 
     As described above, the optical cable connection closure  60  according to the present embodiment also allows the dimension of the closure body  61  in the Z direction to be reduced, and the closure body  61  to be made more compact. It is thereby possible to make the closure body  61  suspended from the messenger wire  3  inconspicuous, and to improve the esthetic appeal of the optical cable connection closure  60  suspended from the messenger wire  3 . 
     As described above, the first housing section  62  and the second housing section  63  sandwich the frame  64  in the Y direction, and are configured so as to be exposed to the exterior. It is thereby possible to arrange the trunk optical cables  5 A to  5 D from a predetermined orientation along the Y direction with respect to the first layer  66   a  provided in the first housing section  63 . It is also possible to arrange the optical connectors  8 A to  8 D from a direction opposite that of the orientation used when arranging the trunk optical cables  5 A to  5 D with respect to the third layer  67  provided in the second housing section  63 . Good ease of work is thereby ensured. 
     Preferred embodiments of the present invention have been described above, but the present invention is not limited to the embodiments described above, and various modifications and other applications are possible within the scope of the claims. 
     For example, in the first embodiment, the fourth layer  29  is included in the third layer  28 , but it may instead be included in the second layer  15 . In the first embodiment, the entirety of the first through third layers  14 ,  15 , and  28  overlap in the Y direction, but it is also acceptable for parts thereof to overlap. This also yields the abovementioned effect of improving the esthetic appeal of the optical cable connection closure  1 . 
     The closure body  61  housing the trunk optical cables  5 A to  5 D in the second embodiment described above may be covered by a protective cover not shown in the drawings. Various optical cables may be applied as the trunk optical cables  5 A to  5 D and the branching optical cables  7 A to  7 D. 
     The present invention may also be considered to be a method of splitting an optical cable (or an optical cable connection method) for housing a trunk optical cable and optically connecting a branching optical cable to a second optical cable via an optical connector.