Patent Publication Number: US-2023141383-A1

Title: Housing structure, pulling-end-equipped optical cable, and method for manufacturing housing structure

Description:
TECHNICAL FIELD 
     The present disclosure relates to a housing structure, a pulling-end-equipped optical cable, and a method for manufacturing a housing structure. 
     BACKGROUND 
     Patent Literature 1 discloses a cable pulling terminal structure used at the time of pulling an optical cable with a pulling device. 
     PATENT LITERATURE 
     
         
         Patent Literature 1: Japanese Patent Application Laid-open Publication No. 2010-217316 
       
    
     An optical cable can be laid from outside a station building to inside thereof by pulling a pulling part of a pulling-end-equipped optical cable. The laying task inside the station building after pulling-in the optical cable can be facilitated by attaching optical connectors in advance to respective end parts of optical fibers of the optical cable and by housing the optical connectors inside a pulling terminal structure. However, in cases of housing a multitude of optical connectors, the housing may become large. It should be noted that there are demands to reduce the size not only of housings for pulling-end-equipped optical cables, but also of housings configured to house a multitude of optical connectors provided to an end part of an optical cable. 
     SUMMARY 
     One or more embodiments of the present invention reduce the size of a housing body configured to house a multitude of optical connectors. 
     One or more embodiments of the invention relate to a housing structure including: an optical cable including optical fibers; connector units branching off from the optical cable; and a housing body configured to house the connector units. Each of the connector units includes: a first tube configured such that a plurality of the optical fibers are passed therethrough; second tubes, each configured such that a plurality of the optical fibers branching off from the first tube are passed therethrough; and a connector group constituted by optical connectors provided respectively at an end part of the respective second tubes. The respective connector groups of the connector units are located at different positions from one another in a length direction. In case where the shortest connector unit is defined as a first connector unit, the respective first tubes of the connector units other than the first connector unit are present in a region occupied in the length direction by the connector group of the first connector unit. In relation to at least one of the connector units whose connector group is located on a leading-end side with respect to the connector group of the first connector unit, the second tubes of the connector unit that is next longer than the at least one connector unit are present in a region occupied in the length direction by the connector group of the at least one connector unit. 
     One or more embodiments of the invention relate to a pulling-end-equipped optical cable including: an optical cable including optical fibers; connector units branching off from the optical cable; and a housing body configured to house the connector units. Each of the connector units includes: a first tube configured such that a plurality of the optical fibers are passed therethrough; second tubes, each configured such that a plurality of the optical fibers branching off from the first tube are passed therethrough; and a connector group constituted by optical connectors provided respectively at an end part of the respective second tubes. The respective connector groups of the connector units are located at different positions from one another in a length direction. In case where the shortest connector unit is defined as a first connector unit, the respective first tubes of the connector units other than the first connector unit are present in a region occupied in the length direction by the connector group of the first connector unit. In relation to at least one of the connector units whose connector group is located on a leading-end side with respect to the connector group of the first connector unit, the second tubes of the connector unit that is next longer than the at least one connector unit are present in a region occupied in the length direction by the connector group of the at least one connector unit. 
     One or more embodiments of the invention relate to a method for manufacturing a housing structure, the method involving: creating connector units that branch off from an optical cable and that each include a first tube, second tubes, and a connector group constituted by optical connectors provided respectively at an end part of the respective second tubes, by passing a plurality of optical fibers that branch off from the optical cable through the respective first tube, passing a plurality of the optical fibers that branch off from the first tube through the respective second tubes, and providing the optical connectors at an end part of the optical fibers that have been passed through the respective second tubes; and housing the connector units in a housing body in such a manner that: in case where the shortest connector unit is defined as a first connector unit, the respective first tubes of the connector units other than the first connector unit are present in a region occupied in a length direction by the connector group of the first connector unit; and, in relation to at least one of the connector units whose connector group is located on a leading-end side with respect to the connector group of the first connector unit, the second tubes of the connector unit that is next longer than the at least one connector unit are present in a region occupied in the length direction by the connector group of the at least one connector unit. 
     Other features of the present invention will be disclosed in the Description and Drawings as described below. 
     According to the present invention, it is possible to reduce the size of a housing body configured to house optical connectors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a diagram illustrating an outer appearance of a pulling-end-equipped optical cable  100  according to one or more embodiments.  FIG.  1 B  is a diagram illustrating an inner structure of the pulling-end-equipped optical cable  100  according to one or more embodiments. 
         FIG.  2    is a diagram illustrating an optical cable  1 . 
         FIG.  3    is a diagram illustrating a terminal structure  50  according to a modified example. 
         FIG.  4    is a diagram illustrating connector units  20  extending out from a lead-out part of an optical cable  1 . 
         FIGS.  5 A and  5 B  are diagrams illustrating a leading end part of an arbitrary connector unit  20 . 
         FIG.  6 A  is a diagram illustrating an optical connector  10  according to one or more embodiments.  FIG.  6 B  is a diagram illustrating a state in which a tubular member  18  of  FIG.  6 A  has been removed.  FIG.  6 C  is a diagram illustrating a state in which the tubular member  18  and second tube  22  of  FIG.  6 A  have been removed. 
         FIG.  7    is an exploded view of the optical connector  10  according to one or more embodiments. 
         FIG.  8    is a diagram illustrating an arrangement of connector groups  23  according to one or more embodiments. 
         FIG.  9    is a diagram illustrating a first comparative example. 
         FIGS.  10 A and  10 B  are diagrams for comparing arrangements of connector groups  23 . 
         FIG.  10 A  illustrates an arrangement of connector groups  23  according to one or more embodiments. 
         FIG.  10 B  illustrates an arrangement of connector groups  23  according to a second comparative example. 
         FIG.  11    is a flowchart of a method for manufacturing a pulling-end-equipped optical cable  100  according to one or more embodiments. 
         FIGS.  12 A to  12 F  are diagrams illustrating how the pulling-end-equipped optical cable  100  of one or more embodiments is manufactured. 
         FIG.  13    is a diagram illustrating how an optical cable is laid from outside a station building to inside thereof by pulling a pulling part of a pulling-end-equipped optical cable. 
     
    
    
     DETAILED DESCRIPTION 
     At least the following features are disclosed in the Description and Drawings as described below. 
     Disclosed is a housing structure including: an optical cable including optical fibers; connector units branching off from the optical cable; and a housing body configured to house the connector units. Each of the connector units includes: a first tube configured such that a plurality of the optical fibers are passed therethrough; second tubes, each configured such that a plurality of the optical fibers branching off from the first tube are passed therethrough; and a connector group constituted by optical connectors provided respectively at an end part of the respective second tubes. The respective connector groups of the connector units are located at different positions from one another in a length direction. In case where the shortest connector unit is defined as a first connector unit, the respective first tubes of the connector units other than the first connector unit are present in a region occupied in the length direction by the connector group of the first connector unit. In relation to at least one of the connector units whose connector group is located on a leading-end side with respect to the connector group of the first connector unit, the second tubes of the connector unit that is next longer than the at least one connector unit are present in a region occupied in the length direction by the connector group of the at least one connector unit. With this housing structure, it is possible to reduce the diameter and length of the housing body and thereby reduce the size of the housing body. 
     In case where the second tubes of an [N+1]-th connector unit are present in a region occupied in the length direction by the connector group of an N-th connector unit, a distance in the length direction between the connector group of the N-th connector unit and the connector group of the [N+1]-th connector unit may be shorter than a distance in the length direction between the connector group of the first connector unit and the connector group of a second connector unit, where: the second connector unit is the connector unit that is next longer than the first connector unit; the N-th connector unit is an arbitrary connector unit; and the [N+1]-th connector unit is the connector unit that is next longer than the N-th connector unit. In this way, the housing body can be shortened. 
     In relation to one of the connector units whose connector group is located on the leading-end side with respect to the connector group of the N-th connector unit, the second tubes of another 5 of the connector units may be present in a region occupied in the length direction by the connector group of the one connector unit. In this way, the housing body can be further shortened. 
     Also disclosed is a pulling-end-equipped optical cable including: an optical cable including optical fibers; connector units branching off from the optical cable; and a housing body configured to house the connector units. Each of the connector units includes: a first tube configured such that a plurality of the optical fibers are passed therethrough; second tubes, each configured such that a plurality of the optical fibers branching off from the first tube are passed therethrough; and a connector group constituted by optical connectors provided respectively at an end part of the respective second tubes. The respective connector groups of the connector units are located at different positions from one another in a length direction. In case where the shortest connector unit is defined as a first connector unit, the respective first tubes of the connector units other than the first connector unit are present in a region occupied in the length direction by the connector group of the first connector unit. In relation to at least one of the connector units whose connector group is located on a leading-end side with respect to the connector group of the first connector unit, the second tubes of the connector unit that is next longer than the at least one connector unit are present in a region occupied in the length direction by the connector group of the at least one connector unit. In this way, the size of the housing body can be reduced, and the optical cable can be pulled easily. 
     The pulling-end-equipped optical cable may further include a braided tube configured to house the housing body, wherein a pulling part is provided at an end part of the braided tube, and wherein an end part of the braided tube on an opposite side from the side with the pulling part is fixed to the optical cable. In this way, tensile force during pulling is applied to the braided tube and does not directly act on the housing body, and thus, the diameter of the housing body can be reduced. 
     Also disclosed is a method for manufacturing a housing structure, the method involving: creating connector units that branch off from an optical cable and that each include a first tube, second tubes, and a connector group constituted by optical connectors provided respectively at an end part of the respective second tubes, by passing a plurality of optical fibers that branch off from the optical cable through the respective first tube, passing a plurality of the optical fibers that branch off from the first tube through the respective second tubes, and providing the optical connectors at an end part of the optical fibers that have been passed through the respective second tubes; and housing the connector units in a housing body in such a manner that: in case where the shortest connector unit is defined as a first connector unit, the respective first tubes of the connector units other than the first connector unit are present in a region occupied in a length direction by the connector group of the first connector unit; and in relation to at least one of the connector units whose connector group is located on a leading-end side with respect to the connector group of the first connector unit, the second tubes of the connector unit that is next longer than the at least one connector unit are present in a region occupied in the length direction by the connector group of the at least one connector unit. In this way, it is possible to reduce the diameter and length of the housing body and thereby reduce the size of the housing body. 
     Configuration of Pulling-End-Equipped Optical Cable  100 : 
       FIG.  1 A  is a diagram illustrating an outer appearance of a pulling-end-equipped optical cable  100  according to one or more embodiments.  FIG.  1 B  is a diagram illustrating an inner structure of the pulling-end-equipped optical cable  100  according to one or more embodiments. 
     In the following description, as illustrated in  FIG.  1 A , the length direction of the pulling-end-equipped optical cable  100  is referred to as “front-rear direction”, wherein the leading end side as viewed from the pulling-end-equipped optical cable  100  is referred to as “front”, and the opposite side is referred to as “rear”. The front side may be referred to as “leading end side”, and the rear side may be referred to as “base end side”. 
     The pulling-end-equipped optical cable  100  is an optical cable having a pulling part at an end part thereof. As illustrated in  FIG.  13   , an optical cable  1  can be laid from outside a station building to inside thereof by pulling the pulling part of the pulling-end-equipped optical cable  100 . The pulling-end-equipped optical cable  100  includes an optical cable  1  and a terminal structure  50 . 
       FIG.  2    is a diagram illustrating the optical cable  1 . 
     The optical cable  1  is a cable that houses a multitude of optical fibers  3  inside an outer sheath  4 . The optical cable  1  includes a plurality of optical fiber units  2 , a wrapping tape  5 , and the aforementioned outer sheath  4 . The optical fiber unit  2  is a unit in which a plurality of optical fibers  3  are bundled. Herein, the optical fiber unit  2  is constituted by bundling a plurality of intermittently connected optical fiber ribbons with a bundling member. Note that the optical cable  1  of one or more embodiments includes 288 optical fiber ribbons (optical fiber tapes), each constituted by twelve optical fibers  3 , and hence includes a total of 3,456 optical fibers  3 . The number of optical fiber ribbons and optical fibers  3 , however, is not limited to the above. The plurality of optical fiber units  2  are housed inside the outer sheath  4  in a state wrapped by the wrapping tape  5 . Tension members  6  and rip cords  7  are embedded within the outer sheath  4 . 
     A multitude of optical fibers  3  (optical fiber ribbons) extend out from a lead-out part of the optical cable  1 . In one or more embodiments, 288 optical fiber ribbons extend out from the lead-out part of the optical cable  1 . (Note that, in  FIG.  1 B , the number of optical fiber ribbons is reduced for the sake of brevity.) An optical connector  10  is attached to an end part of the optical fibers  3 . The optical connector  10  of one or more embodiments is constituted by a 24-fiber MPO connector. Hence, 144 optical connectors  10  are attached in the optical cable  1  of one or more embodiments. (Note that, in  FIG.  1 B , the number of optical connectors  10  is reduced for the sake of brevity.) The optical fibers  3  (optical fiber ribbons) leading out from the optical cable  1  are passed through later-described protection tubes (first tubes  21  and second tubes  22 ). The structure extending out from the lead-out part of the optical cable  1  (i.e., connector units  20  including optical connectors  10 ) will be described further below. 
     The terminal structure  50  is a structure provided to a terminal of the optical cable  1 . The terminal structure  50  of one or more embodiments is a pulling terminal structure having a pulling part  50 A. The terminal structure  50  of one or more embodiments is a structure that enables pulling of the optical cable  1  while housing the connector units  20  (described below). The pulling part  50 A is a section for pulling the optical cable  1 . The terminal structure  50  includes a housing body  51  and a braided tube  55 . 
     The housing body  51  is a housing member configured to house a plurality of optical connectors  10  (and later-described connector units  20 ). The housing body  51  of one or more embodiments includes a housing tube  52 , a housing tube fixing part  53 , and a front member  54 . The interior space within the housing body  51  constitutes a housing space for housing the optical connectors  10  (and the later-described connector units  20 ). Stated differently, the space surrounded by the housing tube  52 , the housing tube fixing part  53 , and the front member  54  serves as the housing space. It should be noted that a structure constituted by the optical cable  1  and the housing body  51  housing the plurality of optical connectors  10  (and the later-described connector units  20 ) may also be referred to as “housing structure”. 
     The housing tube  52  is a cylindrical (tubular) member configured to house the optical connectors  10 . The housing tube  52  of one or more embodiments houses the connector units  20  (described later) extending out from the lead-out part of the optical cable  1 . The housing tube  52  functions to protect the connector units  20 . In one or more embodiments, the housing tube  52  is constituted by a tube having flexibility (i.e., a flexible tube), and more specifically, a corrugated pipe. Note, however, that the housing tube  52  may be constituted by a type of tube/pipe different from the corrugated pipe, so long as the housing tube has a certain degree of flexibility that makes bending possible in an underground conduit as illustrated in  FIG.  13   . The housing tube  52  is located inside the braided tube  55 . The housing tube fixing part  53  is located on the rear side of the housing tube  52 . The housing tube  52  is fixed to the optical cable  1  via the housing tube fixing part  53 . The front member  54  is located on the front side of the housing tube  52 . 
     The housing tube fixing part  53  is a member configured to fix the housing tube  52  to the optical cable  1 . The housing tube fixing part  53  is located in the vicinity of the lead-out part  1 A of the optical cable  1 . The housing tube  52  is attached to the front side of the housing tube fixing part  53 . Note that the housing tube fixing part  53  reinforces the housing tube  52  by being fitted to the rear edge of the housing tube  52 . 
     The front member  54  is a member constituting a front part of the housing body  51 . The front member  54  reinforces the housing tube  52  by being fitted to the front edge of the housing tube  52 . 
     The braided tube  55  is a member made by braiding fiber members in a tube shape. Stated differently, the braided tube  55  is a tube made by braiding fiber members in a mesh form. The fiber members constituting the braided tube  55  may be, for example, resin fibers or metal wiring (wires). The leading end of the braided tube  55  is provided with the pulling part  50 A. When the pulling part  50 A is pulled, a large tensile force is applied to the braided tube  55 , but the braided tube  55 , which is constituted by a multitude of fiber members, has sufficient durability against such tensile force. Further, the braided tube  55  has a certain degree of flexibility that makes bending possible in an underground conduit as illustrated in  FIG.  13   . 
     The housing body  51  is located inside the braided tube  55 . The braided tube  55  functions to protect the housing body  51  from friction with the inner wall surface of an underground conduit as illustrated in  FIG.  13   . Also, the end part of the optical cable  1  is housed inside the braided tube  55 . The braided tube  55 &#39;s end part on the base end side is fixed to the optical cable  1  by the tube fixing part  56 . For example, the tube fixing part  56  is constituted by a heat-shrinkable tube, and the braided tube  55  is fixed to the optical cable  1  by sandwiching the rear edge of the braided tube  55  between the heat-shrinkable tube and the optical cable  1 . The braided tube  55 &#39;s end part on the leading end side is provided with the pulling part  50 A. The pulling part  50 A is a section configured to be pulled with a pulling device such as a winch. The pulling part  50 A may be referred to as “pulling end”. The pulling part  50 A of one or more embodiments is constituted by forming an excessive-length portion at the leading end of the braided tube  55  in a ring shape. That is, in one or more embodiments, the pulling part  50 A is formed integrally with the braided tube  55 . Note, however, that the pulling part  50 A is not limited to such a configuration, and may be provided to a separate member other than the braided tube  55 . 
       FIG.  3    is a diagram illustrating a terminal structure  50  according to a modified example. The terminal structure  50  of the modified example includes a housing body  51 . As illustrated in this modified example, the terminal structure  50  does not have to include the aforementioned braided tube  55 . The housing body  51  of the modified example includes a housing tube  52 , a housing tube fixing part  53 , and a front member  54 , and the front member  54  is provided with a pulling part  50 A. As illustrated in this modified example, the pulling part  50 A does not have to be provided to the braided tube  55 , and may be provided to the front part of the housing body  51 . 
     It should be noted that, as regards the terminal structure  50  of one or more embodiments as illustrated in  FIGS.  1 A and  1 B , tensile force during pulling is applied directly to the braided tube  55 , and does not directly act on the housing tube  52 . Hence, according to one or more embodiments, it is possible to suppress destruction of the housing tube  52  caused by application of tensile force on the housing tube  52 . In contrast, as regards the terminal structure  50  of the modified example as illustrated in  FIG.  3   , tensile force during pulling is applied to the housing tube  52 . The housing tube  52 , which is constituted by a corrugated pipe, is relatively weak against tensile force. Hence, if the housing tube is to be provided with a structure that can withstand the tensile force during pulling, it will be difficult to reduce the diameter of the housing tube  52 . In contrast, in one or more embodiments, the tensile force during pulling does not act on the housing tube  52 , and thus, the diameter of the housing tube  52  can be reduced. 
     Conversely, the more the housing tube  52 &#39;s diameter is reduced, the smaller the housing space inside the housing body  51  becomes. Note, however, that with one or more embodiments, a multitude of optical connectors  10  (144 optical connectors  10  in this example) can be housed inside the small housing space of the housing body  51 , as will be described below. 
     Connector Units  20 : 
       FIG.  4    is a diagram illustrating the connector units  20  extending out from the lead-out part of the optical cable  1 .  FIGS.  5 A and  5 B  are diagrams illustrating a leading end part of an arbitrary connector unit  20 . 
     In one or more embodiments, a plurality of (in this example, nine) connector units  20  branch off and extend out from the lead-out part  1 A of the optical cable  1 . The plurality of connector units  20  are housed inside the housing space of the housing body  51 . In  FIG.  4   , for the sake of explanation, the housing space of the housing body  51  is illustrated in an enlarged/expanded manner, and the connector units  20  are illustrated with spaces therebetween. 
     In the description below, the connector units  20  may be referred as the first connector unit  20 A, the second connector unit  20 B, . . . , the ninth connector unit  20 I, in order from the shortest connector unit. Hence, if an arbitrary connector unit  20  (except for the longest connector unit  20 ) is defined as the N-th connector unit  20 , the connector unit  20  that is next longer than the N-th connector unit  20  can be expressed as the [N+1]-th connector unit  20 . 
     A single connector unit  20  includes: a plurality of (in this example, sixteen) optical connectors  10 ; a single first tube  21 ; and the same number of second tubes  22  as the optical connectors  10 . Note that the optical connectors  10  (the sixteen optical connectors  10  in this example) of a single connector unit  20  may also be referred to as “connector group  23 ”. So, stated differently, a single connector unit  20  includes: a single first tube  21 ; a plurality of second tubes  22 ; and a connector group  23 . 
     The first tube  21  is a member located on the base-end side with respect to the second tubes  22 , and is a protection tube for protecting a plurality of the optical fibers  3 . The first tube  21  may also be referred to as “primary tube”. A plurality of the optical fibers  3  branching off from the optical cable  1  are passed through the first tube  21 . In this example, 384 optical fibers (i.e., 32 pieces of 12-fiber optical fiber ribbons) are passed through the first tube  21 . Note, however, that the number of optical fibers to be passed through the first tube  21  is not limited thereto. 
     Each second tube  22  is a member located on the base-end side with respect to the optical connector  10 , and is a protection tube for protecting the optical fibers extending out from the optical connector  10 . A plurality of the optical fibers  3  branching off from the first tube  21  are passed through the respective second tube  22 . The second tube  22  may also be referred to as “secondary tube”. Each second tube  22  is arranged between the first tube  21  and the optical connector  10 . As will be described below, the front end part of the second tube  22  is attached to the optical connector  10 . The rear end part of the second tube  22  is arranged at a branching part of the first tube  21 . 
     Since a plurality of optical fibers branching off from the first tube  21  are passed through each second tube  22 , the number of optical fibers passed through each second tube  22  is smaller than the number of optical fibers passed through the first tube  21 . In this example, the 384 optical fibers (i.e., 32 pieces of 12-fiber optical fiber ribbons) passed through the first tube  21  are separated into sixteen branches, and 24 optical fibers (i.e., 2 pieces of 12-fiber optical fiber ribbons) are passed through each second tube  22 . Note, however, that the number of optical fibers to be passed through each second tube  22  is not limited thereto. In one or more embodiments, a single connector unit  20  includes sixteen second tubes  22 . Note, however, that the number of second tubes  22  (or the number of branches of optical fibers) in each connector unit  20  is not limited thereto. 
     The first tubes  21  and the second tubes  22  are each constituted by a braided tube. A braided tube is a member made by braiding fiber members in a tube shape. In one or more embodiments, the first tubes  21  and the second tubes  22  are constituted by polyester resin fibers. Note, however, that the material for the first tubes  21  and the second tubes  22  is not limited to polyester. Further, the first tubes  21  and the second tubes  22  do not necessarily have to be constituted by braided tubes. For example, the first tubes  21  and the second tubes  22  may be constituted by silicone tubes. 
     Each second tube  22  has a smaller inner diameter and outer diameter than the first tube  21 , as each contains a smaller number of optical fibers. Note, however, that the number of second tubes  22  is greater than the number of first tubes  21 , and in one or more embodiments, there are sixteen second tubes  22  with respect to a single first tube  21 . Further, in one or more embodiments, the total of cross-sectional areas of the plurality of (in this example, sixteen) second tubes  22  in a single connector unit  20  is larger than the cross-sectional area of the first tube  21 . Further, in one or more embodiments, the cross-sectional area of a bundle of the plurality of (in this example, sixteen) second tubes  22  in a single connector unit  20  is larger than the cross-sectional area of the first tube  21 . 
     The connector group  23  is an assembly constituted by a plurality of the optical connectors  10 . In this example, each connector group  23  is constituted by sixteen optical connectors  10  (see  FIGS.  5 A and  5 B ). Note, however, that the number of optical connectors  10  constituting the connector group  23  is not limited to sixteen. In this example, each connector group  23  is constituted by four sets of optical connectors  10 , each set including four optical connectors  10  which are located at the same position in the length direction (thus, there are sixteen optical connectors  10  in total). The positions, in the length direction, of the respective sets of optical connectors  10  are gradually shifted from one another. More specifically, the positions, in the length direction, of the respective sets of optical connectors  10  are shifted from one another stepwise by a length worth approximately a single optical connector  10 . If all of the optical connectors  10  in the connector group  23  were arranged at the same position in the length direction, the cross-sectional area of the entire connector group  23  would increase, thus making it difficult to house the connector group  23  in the housing body  51 &#39;s small housing space. In contrast, by locating the respective sets of optical connectors  10  at positions that are gradually different from one another in the length direction as in one or more embodiments, the cross-sectional area of the connector group  23  can be reduced, and thus, the connector group  23  can easily be housed in the housing body  51 &#39;s small housing space. Note that, in one or more embodiments, four optical connectors  10  constitute a single set, but the number of optical connectors is not limited thereto. For example, eight optical connectors  10  may constitute a single set, and the connector group  23  may be constituted by two sets of optical connectors  10 . 
     As described above, the housing structure of one or more embodiments includes: an optical cable  1 ; connector units  20  branching off from the optical cable  1 ; and a housing body  51  configured to house the connector units  20 . Each connector unit  20  includes: a first tube  21  configured such that a plurality of optical fibers branching off from the optical cable are passed therethrough; a plurality of second tubes  22 , each configured such that a plurality of optical fibers branching off from the first tube  21  are passed therethrough; and a connector group  23  constituted by a plurality of optical connectors  10  (the same number as the second tubes  22 ) provided respectively at an end part of the respective second tubes  22 . Next, an example of the optical connector  10  will be described. 
       FIG.  6 A  is a diagram illustrating an optical connector  10  according to one or more embodiments.  FIG.  6 B  is a diagram illustrating a state in which a tubular member  18  of  FIG.  6 A  has been removed.  FIG.  6 C  is a diagram illustrating a state in which the tubular member  18  and second tube  22  of  FIG.  6 A  have been removed.  FIG.  7    is an exploded view of the optical connector  10  according to one or more embodiments. 
     The optical connector  10  of one or more embodiments is an MPO connector (a F13-type multi-fiber optical connector as defined in JIS C 5982). The optical connector  10  of one or more embodiments includes a ferrule  11 , a pin clamp  12 , a housing  13 , a coupling  14 , a spring  15 , a spring pusher  16 , and a fixing member  17 . Note, however, that the configuration of the optical connector  10  is not limited thereto, and it will suffice if the optical connector includes a ferrule  11 , a housing  13 , and a fixing member  17 . 
     The ferrule  11  is a member for retaining an end part of the optical fiber  3 . The ferrule  11  of one or more embodiments is an MT ferrule (a F12-type multi-fiber optical connector as defined in JIS C 5981). The ferrule  11  has a plurality of fiber holes, and the optical fibers  3  are passed through and fixed in the respective fiber holes. The pin clamp  12  is arranged on the rear side of the ferrule  11 . The ferrule  11  is pressed toward the front by the spring  15  via the pin clamp  12 . A flange part (collar part) of the ferrule  11  comes into contact with a protrusion (not illustrated) formed on the inner wall surface of the housing  13 , and thereby, the ferrule  11 , which is being pressed toward the front, is prevented from falling out frontward. 
     The housing  13  is a member for housing the ferrule  11  in a retractable manner. The housing  13  houses the ferrule  11 , the pin clamp  12 , the spring  15 , and the spring pusher  16 . Engagement holes  13 A are formed in the respective side surfaces of the housing  13 . The engagement holes  13 A are holes for engagement with the spring pusher  16  (more specifically, claw parts  161 A). 
     The coupling  14  is a member to be provided outside the housing  13 . By sliding the coupling  14  rearward, the optical connector  10  can be detached from an adapter (not illustrated). The spring  15  is an elastic member for pressing the ferrule  11 . The spring  15  is arranged in a compressed and deformed state between the pin clamp  12  and the spring pusher  16 . The spring pusher  16  is a receiving part (spring receiving member) for fixing the rear end of the spring  15  with respect to the housing  13 . The spring pusher  16  includes a pair of aim parts  161  and a fitting part  162 . The aim parts  161  are parts to be engaged with the housing  13 . The spring  15  is to be arranged between the pair of arm parts  161 . A claw part  161 A is formed at an end part of each aim part  161 . The claw parts  161 A engage with the respective engagement holes  13 A of the housing  13 , and thereby, the spring pusher  16  is fixed to the housing  13 . The fitting part  162  is a section for fixing the fixing member  17 . 
     The fixing member  17  is a member for fixing an end part of the second tube  22 . The fixing member  17  includes a fitting part  17 A and a tubular part  171 . The fitting part  17 A is a section to be fixed to the fitting part  162  of the spring pusher  16 . By fitting the fitting part  17 A to the fitting part  162  of the spring pusher  16 , the fixing member  17  is fixed with respect to the housing  13 . The tubular part  171  is a tubular section constituting a rear part of the fixing member  17 . In one or more embodiments, the tubular part  171  is formed in the shape of a circular cylinder. Note, however, that the tubular part  171  may be an elliptic cylinder or a polygon cylinder. The fixing member  17  (and the tubular part  171 ) has a through hole formed therein along the front-rear direction, and the optical fibers  3  (in this example, two optical fiber ribbons) can be passed through this through hole. 
     In one or more embodiments, the tubular part  171  has protrusion parts  171 A. The protrusion parts  171 A are sections (pin-shaped sections) protruding outward from the outer circumferential surface of the tubular part  171 . When the second tube  22  (which is a braided tube) is placed over the tubular part  171 , the protrusion parts  171 A can be inserted in the mesh holes of the second tube  22 . In this way, the second tube  22  gets caught by the tubular part  171 , and thereby, the second tube  22  can be suppressed from getting detached from the tubular part  171 , and the second tube  22  can be retained on the optical connector  10 . Further, since the second tube  22  can be suppressed from getting detached from the tubular part  171 , it is possible to keep protecting the optical fibers  3  which extend out from the rear side of the optical connector  10 . With one or more embodiments, the second tube  22  can be retained on the housing  13  with a simple structure, and thus, the length of the optical connector  10  can be shortened easily. Reduction in the length of the optical connector  10  can in turn reduce the length of the connector group  23 , and as a result, the length L 0  of the housing body  51  can also be shortened. 
     As illustrated in  FIGS.  6 A to  6 C  (and  FIG.  7   ), the fixing member  17  of one or more embodiments further includes a tubular member  18 . The tubular member  18  is a circular-cylindrical member which is separate from the main body of the fixing member  17 . By fitting the tubular member  18  onto the tubular part  171 , the second tube  22  can be sandwiched between the outer circumferential surface of the tubular part  171  and the inner circumferential surface of the tubular member  18 . In this way, the second tube  22  can be suppressed from getting detached from the tubular part  171 . Note, however, that the second tube  22  may be fixed to the fixing member  17  without using the tubular member  18 . 
     The configuration of the optical connector  10  is not limited to the above. Note, however, that the cross-sectional area of the optical connector  10  of one or more embodiments is larger than the cross-sectional area of the second tube  22 . 
     Arrangement of Connector Groups  23  in Respective Connector Units  20 : 
       FIG.  8    is a diagram illustrating an arrangement of connector groups  23  according to one or more embodiments.  FIG.  8    illustrates an alignment of a plurality of connector units  20  of one or more embodiments. 
     As described above, in one or more embodiments, nine pieces (nine units) of connector units  20  are housed in the housing space of the housing body  51 . Hence, in one or more embodiments, nine sets (nine groups) of connector groups  23  are housed in the housing space of the housing body  51 . If the nine connector groups  23  were all arranged at the same position in the length direction, it would be difficult to house the connector groups  23  in the housing body  51 &#39;s small housing space, because the cross-sectional area of each optical connector  10  is relatively large (compared to the cross-sectional area of the first tube  21  or the second tube  22 ). So, in one or more embodiments, the respective connector groups  23  of the connector units  20  are located at different positions in the length direction and gradually shifted from one another. However, when the positions of the connector groups  23  of the respective connector units  20  are gradually shifted from one another in the length direction, the length (dimension in the length direction) of the housing body  51  may become large. To address this, one or more embodiments arrange the connector groups  23  as illustrated in  FIG.  8   , to suppress an increase in the length of the housing body  51 . The arrangement of connector groups  23  of one or more embodiments will be described below. 
     As illustrated in  FIG.  8   , the shortest connector unit  20  among the nine connector units  20  is the first connector unit  20 A. Herein, a region occupied in the length direction by the connector group  23  of the first connector unit  20 A is defined as “region A”. In the region A, in addition to the connector group  23  of the first connector unit  20 A, there are eight first tubes  21  of the other eight connector units  20 . 
     In the region A illustrated in  FIG.  8   , the connector group  23  of the first connector unit  20 A, as well as the eight first tubes  21  of the other eight connector units  20 , are arranged, but not the second tubes  22  of the other eight connector units  20 . Hence, the total of the cross-sectional areas of structures occupying the region A is the total of the cross-sectional area of the connector group  23  of the first connector unit  20 A and the cross-sectional areas of the eight first tubes  21 . 
       FIG.  9    is a diagram illustrating a first comparative example. In the first comparative example, the connector unit  20  does not include the first tube  21 , but instead, the second tubes  22  attached to the respective optical connectors  10  extend up to the lead-out part  1 A of the optical cable  1 . As a result, in the first comparative example, the region A includes the connector group  23  of the first connector unit  20 A and a multitude of second tubes  22  of the other eight connector units  20 . Hence, the total of the cross-sectional areas of structures occupying the region A is the total of the cross-sectional area of the connector group  23  of the first connector unit  20 A and the cross-sectional areas of the second tubes  22  worth eight units (i.e., 128 second tubes  22 ). 
     As described above, the total cross-sectional area of the plurality of (in this example, sixteen) second tubes  22  in a single connector unit  20  is larger than the cross-sectional area of the first tube  21 . So, if the second tubes  22  of other connector units  20  are present in the region A as illustrated in the first comparative example of  FIG.  9   , the total cross-sectional area of structures occupying the region A will increase. (As a result, in the first comparative example, the housing body  51  needs to be made thick (increased in diameter) to increase the housing space.) In contrast, with one or more embodiments illustrated in  FIG.  8   , the region A includes the first tubes  21  of the eight connector units  20  other than the first connector unit  20 A, and thus, the total cross-sectional area of structures occupying the region A can be reduced. In this way, one or more embodiments can reduce the diameter of the housing body  51  (more specifically, the housing tube  52 ). 
     In one or more embodiments, as illustrated in  FIG.  8   , the connector group  23  of the second connector unit  20 B (i.e., the connector unit  20  that is next longer than the first connector unit  20 A) is arranged on the leading-end side with respect to the connector group  23  of the first connector unit  20 A to an extent that the second tubes  22  of the second connector unit  20 B are not present in the region A. With this configuration, the first tube  21  of the second connector unit  20 B will be present in the region A. Further, by arranging the connector group  23  of the second connector unit  20 B in this way, the respective first tubes  21  of other connector units  20  that are longer than the second connector unit  20 B will also be present in the region A. So, by arranging the connector group  23  of the second connector unit  20 B on the leading-end side, i.e., the front side, with respect to the connector group  23  of the first connector unit  20 A to an extent that the second tubes  22  of the second connector unit  20 B are not present in the region A, the connector group  23  of the first connector unit  20 A and the respective first tubes  21  of the other eight connector units  20  will be arranged in the region A. 
     Note that, similar to the first connector unit  20 A, also in relation to the second connector unit  20 B, only the respective first tubes  21  of the other connector units  20  (i.e., the third connector unit  20 C to the ninth connector unit  20 I) are present in a region occupied by the connector group  23  of the second connector unit  20 B (or overlap the connector group  23  of the second connector unit  20 B), and the second tubes  22  of the other connector units  20  are not present (or do not overlap). With this configuration, also in the region occupied by the connector group  23  of the second connector unit  20 B, the cross-sectional area of structures within that region can be reduced. 
     Similarly, also in relation to the third connector unit  20 C and the fourth connector unit  20 D, only the respective first tubes  21  of the other connector units  20  are present in a region occupied by the connector group  23  of that connector unit  20 , and the second tubes  22  of the other connector units  20  are not present. With this configuration, also in the region occupied by the connector group  23  of the third connector unit  20 C or the fourth connector unit  20 D, the cross-sectional area of structures within that region can be reduced. 
     Note that, as illustrated in  FIG.  8   , in the region A (i.e., the region occupied by the connector group  23  of the first connector unit  20 A), there are nine connector units  20  (i.e., the first connector unit  20 A to the ninth connector unit  20 I), including the connector group  23  of the first connector unit  20 A. In contrast, in a region occupied by the connector group  23  of another connector unit  20  different from the first connector unit  20 A, at least structures included in the first connector unit  20 A are not present, and hence, the cross-sectional area of structures within that region decreases. For example, in the region occupied by the connector group  23  of the second connector unit  20 B, there are eight connector units  20  (i.e., the second connector unit  20 B to the ninth connector unit  20 I), but none of the structures of the first connector unit  20 A is present. Hence, the cross-sectional area of structures within that region is smaller compared to the region A. Further, the more the connector group  23  of the connector unit  20  is located toward the leading-end side, the fewer the number of connector units  20  there will be in the region occupied by the connector group  23  of that connector unit  20 , and thus, the smaller the cross-sectional area of structures within that region will be. For example, when comparing the region occupied by the connector group  23  of the second connector unit  20 B and the region E occupied by the connector group  23  of the fifth connector unit  20 E, the cross-sectional area of structures within the region E, which is occupied by the connector group  23  of the fifth connector unit  20 E, is smaller. 
     So, in one or more embodiments, as illustrated in  FIG.  8   , for connector units  20  whose connector group  23  is arranged on the leading-end side, the second tubes  22  of other connector units  20  are permitted to be present in the region occupied by the connector group  23  of the connector unit  20  concerned. For example, the second tubes  22  of the sixth connector unit  20 F (i.e., the connector unit  20  that is next longer than the fifth connector unit  20 E) are present in the region E occupied by the connector group  23  of the fifth connector unit  20 E. With this configuration, in one or more embodiments, the distance in the length direction between the connector group  23  of the fifth connector unit  20 E and the connector group  23  of the sixth connector unit  20 F can be reduced. As a result, in one or more embodiments, the length L 0  of the housing body  51  can be shortened. 
     Similarly, in relation to one of the connector units  20  (e.g., any one of the sixth connector unit  20 F to the eighth connector unit  20 H) whose connector group  23  is located on the leading-end side with respect to the connector group  23  of the fifth connector unit  20 E, the second tubes  22  of another of the connector units  20  (e.g., the seventh connector unit  20 G) are present in a region occupied by the connector group  23  of the one connector unit  20  (e.g., the sixth connector unit  20 F, or overlap the connector group  23  of the one connector unit  20 ). With this configuration, it is possible to reduce also the distance in the length direction between the connector groups  23  which are arranged on the leading-end side with respect to the connector group  23  of the fifth connector unit  20 E, and thus, the length L 0  of the housing body  51  can be shortened. 
       FIGS.  10 A and  10 B  are diagrams for comparing arrangements of connector groups  23 .  FIG.  10 A  illustrates an arrangement of connector groups  23  according to one or more embodiments.  FIG.  10 B  illustrates an arrangement of connector groups  23  according to a second comparative example. 
     In the second comparative example illustrated in  FIG.  10 B , for all of the connector units  20 , the second tubes  22  of other connector units  20  are not present in a region occupied in the length direction by any connector group  23 . Stated differently, for all of the connector units  20  except for the longest ninth connector unit  20 I, the respective first tubes  21  of the other connector units  20  are present in a region occupied in the length direction by any connector group  23 . Hence, in the second comparative example, it is necessary to widen the distance in the length direction between the connector groups  23  for all of the connector units  20 . As a result, in the second comparative example, the distance in the length direction between the connector group  23  of the fifth connector unit  20 E and the connector group  23  of the sixth connector unit  20 F is wider compared to one or more embodiments illustrated in  FIG.  10 A . Similarly, in the second comparative example, also in relation to a connector unit  20  (e.g., the sixth connector unit  20 F) whose connector group  23  is located on the leading-end side with respect to the connector group  23  of the fifth connector unit  20 E, the distance in the length direction between the connector group  23  of the connector unit  20  concerned and the connector group  23  of the next longer connector unit  20  is wider compared to one or more embodiments. As a result, the length L 1  of the housing body  51  of the second comparative example becomes longer than the length L 0  of the housing body  51  of one or more embodiments. 
     As described above, in the housing structure of one or more embodiments, the respective first tubes  21  of the connector units  20  other than the first connector unit  20 A, which is the shortest connector unit, are present in a region A occupied in the length direction by the connector group  23  of the first connector unit  20 A. In this way, one or more embodiments can reduce the diameter of the housing body Si. On the other hand, in relation to at least one of the connector units  20  (e.g., the fifth connector unit  20 E) whose connector group  23  is located on the leading-end side with respect to the connector group  23  of the first connector unit  20 A, the second tubes  22  of the connector unit  20  (e.g., the sixth connector unit  20 F) that is next longer than the aforementioned connector unit  20  are present in a region (e.g., region E) occupied in the length direction by the connector group  23  of the aforementioned connector unit  20 . In this way, not only the diameter of the housing body  51 , but also the length of the housing body  51  can be reduced. 
     Further, in one or more embodiments, in case where the second tubes  22  of an [N+1]-th connector unit  20  are present in a region occupied in the length direction by the connector group  23  of an N-th connector unit  20  (for example, in case where N=5), the distance in the length direction between the connector group  23  of the N-th connector unit  20  and the connector group  23  of the [N+1]-th connector unit  20  is shorter than the distance in the length direction between the connector group  23  of the first connector unit  20 A and the connector group  23  of the second connector unit  20 B, where: the N-th connector unit  20  is an arbitrary connector unit  20 ; and the [N+1]-th connector unit  20  is the connector unit  20  that is next longer than the N-th connector unit  20 . In this way, the length L 0  of the housing body  51  can be shortened. 
     Furthermore, in one or more embodiments, in relation to one of the connector units  20  (e.g., the [N+1]-th connector unit  20 ; the sixth connector unit  20 F) whose connector group  23  is located on the leading-end side with respect to the connector group  23  of the N-th connector unit  20  (e.g., N=5; the fifth connector unit  20 E), the second tubes  22  of another of the connector units  20  (e.g., the [N+2]-th connector unit  20 ; the seventh connector unit  20 G) are present in a region occupied in the length direction by the connector group  23  of the aforementioned one connector unit. In this way, the distance in the length direction between the connector groups  23  located on the leading-end side with respect to the connector group  23  of the N-th connector unit  20  can also be reduced, and thus, the length L 0  of the housing body  51  can be further shortened. Note, however, that it is not necessary to reduce the distance between all of the connector groups  23  located on the leading-end side with respect to the connector group  23  of the N-th connector unit  20 . 
     Method for Manufacturing Pulling-End-Equipped Optical Cable  100 : 
       FIG.  11    is a flowchart of a method for manufacturing a pulling-end-equipped optical cable  100  according to one or more embodiments.  FIGS.  12 A to  12 F  are diagrams illustrating how the pulling-end-equipped optical cable  100  of one or more embodiments is manufactured. 
     First, a worker prepares the terminal structure  50  of one or more embodiments (S 101 ). More specifically, the worker prepares the aforementioned braided tube  55  and the housing body  51  (e.g., the housing tube  52 , the housing tube fixing part, and the front member). Also, the worker prepares a heat-shrinkable tube constituting the tube fixing part  56 . Note that the worker passes the optical cable  1  through the heat-shrinkable tube in advance. 
     Next, the worker leads out the optical fibers  3  from the optical cable  1  (S 102 ; see  FIG.  12 A ). Further, the worker passes a plurality of optical fibers that have been branched off from the optical cable through the respective first tubes  21 , and also passes a plurality of the optical fibers  3  that have been branched off from each first tube  21  through the respective second tubes  22  (S 103 ). Note that the worker cuts the optical fibers  3  (optical fiber ribbons) leading out from the optical cable  1  such that the connector units  20 , after completion, respectively have predetermined lengths. Cutting of the optical fibers  3  may be performed before passing the optical fibers through the first tubes  21  and second tubes  22 , or after passing the optical fibers through the first tubes  21  and second tubes  22 . 
     Next, the worker attaches the optical connectors  10  to the respective end part of the optical fibers  3  (optical fiber ribbons) passed through the respective second tubes  22  (S 104 ; see  FIG.  12 B ). The worker also fixes the optical connector  10  to the end part of each second tube  22  (S 105 ; see  FIGS.  6 A to  6 C ). Note that the worker fixes the opposite-side end part of the second tubes  22  to the respective first tube  21  (not illustrated). By fixing the optical connectors  10  to the respective end parts of all of the second tubes  22 , assembly of the plurality of connector units  20  is completed. 
     Note that, in one or more embodiments, when the plurality of completed connector units  20  are arranged along the length direction, the respective first tubes  21  of the connector units  20  other than the first connector unit  20 A, which is the shortest connector unit, are present in a region A occupied in the length direction by the connector group  23  of the first connector unit  20 A. Further, in relation to at least one of the connector units  20  (e.g., the fifth connector unit  20 E) whose connector group  23  is located on the leading-end side with respect to the connector group  23  of the first connector unit  20 A, the second tubes  22  of the connector unit  20  (e.g., the sixth connector unit  20 F) that is next longer than the aforementioned connector unit  20  are present in a region (e.g., region E) occupied in the length direction by the connector group  23  of the aforementioned connector unit  20 . The worker cuts the optical fibers leading out from the optical cable into predetermined lengths in such a manner that the connector units  20  are arranged as described above (see  FIG.  12 A ). 
     After assembling the connector units  20 , the worker assembles the housing body  51  (S 106 ; see  FIG.  12 C ). In this example, the worker assembles the housing body  51  by attaching the housing tube fixing part to the optical cable, and attaching the housing tube and the front member while housing the connector units  20 . Note that, at this stage, the housing structure, wherein the connector units  20  are housed inside the housing body  51  as illustrated in  FIG.  8   , is completed. Further, in cases where the terminal structure  50  has a structure as illustrated in  FIG.  3   , manufacture of a pulling-end-equipped optical cable  100  is completed at the stage of S 105 . 
     In one or more embodiments, after assembling the housing body  51 , the housing body  51  is housed inside the braided tube  55  (S 107 ). At this time, as illustrated in  FIG.  12 D , the worker slides the braided tube  55  over the housing body  51  from the front side, to arrange the housing tube  52  inside the braided tube  55 . Further, as illustrated in  FIG.  12 E , the worker arranges the end part of the braided tube  55  onto the outer circumference of the optical cable  1  and also slides the heat-shrinkable tube, which has been provided on the optical cable  1  in advance, over the end part of the braided tube  55 , to arrange the end part of the braided tube  55  between the optical cable  1  and the heat-shrinkable tube. 
     Finally, the worker heats the heat-shrinkable tube, to fix the end part of the braided tube  55  to the optical cable  1 . In this way, as illustrated in  FIG.  12 F , manufacturing of the pulling-end-equipped optical cable  100  is completed. 
     As described above, in the manufacturing method of one or more embodiments: a plurality of optical fibers that branch off from an optical cable are passed through respective first tubes  21 ; a plurality of the optical fibers that branch off from each first tube  21  are passed through respective second tubes  22 ; and optical connectors  10  are respectively provided at an end part of the optical fibers that have been passed through the respective second tubes  22  (S 103 , S 104 ). This thereby creates connector units  20  that branch off from the optical cable and that each include a first tube  21 , second tubes  22 , and a connector group  23  constituted by the optical connectors  10  provided respectively at an end part of the respective second tubes  22 . Further, in one or more embodiments, by housing the connector units  20  in a housing body  51 , a housing structure (or pulling-end-equipped optical cable  100 ) is manufactured. Further, in the manufacturing method of one or more embodiments, the respective first tubes  21  of the connector units  20  other than the first connector unit  20 A, which is the shortest connector unit, are present in a region A occupied in the length direction by the connector group  23  of the first connector unit  20 A. In this way, one or more embodiments can reduce the diameter of the housing body  51 . On the other hand, in relation to at least one of the connector units  20  (e.g., the fifth connector unit  20 E) whose connector group  23  is located on the leading-end side with respect to the connector group  23  of the first connector unit  20 A, the second tubes  22  of the connector unit  20  (e.g., the sixth connector unit  20 F) that is next longer than the aforementioned connector unit  20  are present in a region (e.g., region E) occupied in the length direction by the connector group  23  of the aforementioned connector unit  20 . In this way, not only the diameter of the housing body  51 , but also the length of the housing body  51  can be reduced. 
     Other Embodiments 
     Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 : Optical cable 
               1 A: Lead-out part 
               2 : Optical fiber unit 
               3 : Optical fiber 
               4 : Outer sheath 
               5 : Wrapping tape 
               6 : Tension member 
               7 : Rip cord 
               10 : Optical connector 
               11 : Ferrule 
               11 A: Guide pin 
               12 : Pin clamp 
               13 : Housing 
               13 A: Engagement hole 
               14 : Coupling 
               15 : Spring 
               16 : Spring pusher 
               161 : Arm part 
               161 A: Claw part 
               162 : Fitting part 
               17 : Fixing member 
               17 A: Fitting part 
               171 : Tubular part 
               171 A: Protrusion part 
               18 : Tubular member 
               20 : Connector unit 
               21 : First tube 
               22 : Second tube 
               23 : Connector group 
               50 : Pulling terminal structure 
               50 A: Pulling part 
               51 : Housing body 
               52 : Housing tube 
               53 : Housing tube fixing part 
               54 : Front member 
               55 : Braided tube 
               56 : Tube fixing part 
               100 : Pulling-end-equipped optical cable