Patent Publication Number: US-2022229236-A1

Title: Reinforcing sleeve, reinforcing structure of spliced portion of optical fiber

Description:
TECHNICAL FIELD 
     The present invention relates to a reinforcing sleeve, and a reinforcing structure of a spliced portion of an optical fiber using the reinforcing sleeve. 
     BACKGROUND 
     It is known that a reinforcing sleeve is provided at a fusion spliced portion for reinforcing when fusion splicing optical fiber core wires with each other, for example. 
     Various types of such reinforcing sleeves have been devised. For example, Patent Document 1 discloses a reinforcing sleeve in which a hot melt adhesive tube and a tension member are inserted into a heat-shrinkable tube. 
     RELATED ART 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. 1989-32208 (JP-A-1989-32208) 
       
    
     SUMMARY 
     Problems to be Solved by the Invention 
     An optical fiber tape core wire has been used in recent years as an optical fiber for carrying mass quantity of data at high speed. The optical fiber tape core wire includes a plurality of optical fiber core wires that are placed side by side and bonded with each other, and is used to facilitate packaging inside a cable and to simplify operations. In addition to the optical fiber tape core wire including the plurality of optical fiber core wires that are disposed side by side and fixed and bonded over an entire length by resin, an optical fiber ribbon including the plurality of side-by-side optical fiber core wires bonded with each other at intervals in a longitudinal direction has also been used. Such intermittent bonding between optical fiber core wires improves fiber density, reduces transmission loss due to bending, and facilitates making a single core fiber. Hereinafter, the optical fiber tape core wire and the optical fiber ribbon will be collectively referred to as an optical fiber tape for simplification. 
       FIG. 10A  to  FIG. 10C  show steps for reinforcing a spliced portion of optical fiber tapes using a reinforcing sleeve. First, as shown in  FIG. 10A , optical fiber core wires  101  that are disposed facing each other are butted to each other and fusion bonded with each other by discharging electricity from an electrode  103 . At this time, a reinforcing sleeve  100  is put aside on a side of one of the optical fiber core wires  101 . 
     Next, as shown in  FIG. 10B , the reinforcing sleeve  100  is moved to the spliced portion of the optical fiber core wires  101  (an arrow F in the drawing). Then, as shown in  FIG. 10C , the reinforcing sleeve  100  is heated and shrunk so that the reinforcing sleeve  100  and a plurality of the optical fiber core wires  101  are unified as one body, thereby reinforcing the spliced portion of the plurality of optical fiber core wires  101 . 
       FIG. 11A  is a cross-sectional view of a state shown in  FIG. 10B . As mentioned above, the reinforcing sleeve  100  includes a heat-meltable member  107  and a tension member  109  that are inserted into a heat-shrinkable tube  105 . The heat-meltable member  107  is in a cylindrical shape, and the spliced portion of the side-by-side optical fiber core wires  101  is provided so as to pass through the heat-meltable member  107 . Outer jackets of the optical fiber core wires  101  that are to be passed through the heat-meltable member  107  are removed before splicing. 
       FIG. 11B  is an ideal schematic view of a structure of the reinforcing sleeve  100  when heated. The heat-shrinkable tube  105  shrinks by heating. Also, the heat-meltable member  107  softens by heat, filling up space inside the heat-shrinkable tube  105  after shrinking, and becomes unified with the plurality of optical fiber core wires  101  and the tension member  109 . 
     Here, an upper surface of the tension member  109  (on a side of the optical fiber core wires  101 ) is often formed as a plane. It is expected for the plurality of optical fiber core wires  101  to align with the plane of the upper surface of the tension member  109 , and to be unified with the tension member  109  and the heat-meltable member  107 . 
     However, in reality, as shown in  FIG. 11C , when the heat-shrinkable tube  105  shrinks, the heat-meltable member  107  receives force from its surroundings (arrows G in the drawing), and thus the plurality of optical fiber core wires  101  receive side pressure. As mentioned above, although the optical fiber core wires  101  are expected to align straightly with the plane portion of the upper surface of the tension member  109 , the side pressure, particularly in a width direction, disarranges the optical fiber core wires  101 . For example, part of the optical fiber core wires  101  move away from the tension member  109  to be gathered around the center. 
     Such tendency is more noticeable in particular as a distance between the optical fiber core wires  101  (a pitch) decreases or the number of the optical fiber core wires increases. This tendency is also more noticeable when a diameter of an optical fiber bare wire is small, with less rigidity. Also, this tendency is further noticeable in an intermittently-bonded optical fiber ribbon, in which the plurality of optical fiber core wires are bonded at intervals in a longitudinal direction. 
     If the alignment of the optical fiber core wires  101  is disarranged as above, transmission loss in part of the optical fiber core wires  101  may increase. For this reason, when shrinking the heat-shrinkable tube  105 , the optical fiber core wires  101  are expected to be always unified in a fixed form, without disarrangement of the alignment of each of the optical fiber core wires  101 . 
     The present invention was made in response to the above issue, and it is an object of the present invention to provide a reinforcing sleeve and the like that can efficiently reinforce a spliced portion of optical fiber tapes. 
     Means for Solving Problems 
     To achieve the above object, a first aspect of the present invention is a reinforcing sleeve for collectively reinforcing spliced portions of a plurality of optical fiber core wires that are disposed side by side. The reinforcing sleeve includes a heat-shrinkable tube, a tension member, and a heat-meltable member. The tension member and the heat-meltable member are inserted into the heat shrinkable tube. The heat-meltable member includes a convex portion protruding toward an inner surface side of the heat-meltable member. The convex portion is formed on a side of the tension member at proximity of a center portion of a width direction in a cross section perpendicular to a longitudinal direction of the tube-shaped heat-meltable member. 
     According to the first aspect of the present invention, the convex portion protruding toward the inner surface side is formed on the side of the tension member at proximity of the center portion of the width direction of the tube-shaped heat meltable-member. Thus, the optical fiber core wires can be dispersed toward end portions along the convex portion. This can prevent disarrangement caused by side pressure. 
     A second aspect of the present invention is a reinforcing sleeve for collectively reinforcing spliced portions of a plurality of optical fiber core wires that are disposed side by side. The reinforcing sleeve includes a heat-shrinkable tube, a tension member, and a heat-meltable member. The tension member and the heat-meltable member are inserted into the heat shrinkable tube. The heat-meltable member includes a thick portion having a thickness that is greater than thicknesses of the other parts. The thick portion is formed at proximity of a center portion of a width direction in a cross section perpendicular to a longitudinal direction of the heat-meltable member. 
     The thick portion may be formed on a side of the tension member of the heat-meltable member, and an inner surface side of the heat-meltable member may be formed in a protruding shape protruding toward a center of the heat-meltable member. 
     According to the second aspect of the present invention, an amount of the heat-meltable member per unit circumference length at proximity of the center portion of the width direction of the heat-meltable member is greater than an amount of the heat-meltable member per unit circumference length at proximity of end portions of the width direction of the heat-meltable member. This forms a flow of the heat-meltable member from the center portion toward the end portions at the time of melting the heat-meltable member. Thus, the optical fiber core wires can be dispersed toward the end portions, and this can prevent disarrangement due to side pressure. 
     In addition, the thick portion is in the protruding shape protruding toward the inner surface side, and, when arranging the optical fiber core wires, this protruding shape facilitates dispersing the arrangement of the optical fiber core wires toward the end portion sides. 
     A third aspect of the present invention is a reinforcing sleeve for collectively reinforcing spliced portions of a plurality of optical fiber core wires that are disposed side by side. The reinforcing sleeve includes a heat-shrinkable tube, a tension member, and a heat-meltable member. The tension member and the heat-meltable member are inserted into the heat shrinkable tube. The heat-meltable member includes a first tube-shaped heat-meltable member, and a second heat-meltable member that is disposed at a center portion of a width direction of the first heat-meltable member. 
     The second heat-meltable member may be disposed between the first heat-meltable member and the tension member, and an outer shape of the second heat-meltable member may be formed in a protruding shape protruding toward the first heat-meltable member. 
     The third aspect of the present invention can provide the same effects as the second aspect of the present invention. Also, by disposing further the second heat-meltable member at the center portion of the width direction of the first heat-meltable member, a conventionally used heat-meltable member may be employed as the first heat-meltable member. 
     At this time, the second heat-meltable member is disposed between the first heat-meltable member and the tension member, and the outer shape of the second heat-meltable member is formed in the protruding shape protruding toward the first heat-meltable member. Thus, when arranging the optical fiber core wires, the protruding shape facilitates dispersing the arrangement of the optical fiber core wires toward the end portion sides. 
     A fourth aspect of the present invention is a reinforcing structure of a spliced portion of optical fibers using the reinforcing sleeve according to the first to third aspects of the present invention, in which the heat-meltable member unifies the spliced portion of optical fiber ribbons and the tension member as one body. The optical fiber ribbon includes a plurality of optical fiber core wires that are placed side by side and bonded to each other at intervals in a longitudinal direction. 
     Preferably, the number of the plurality of optical fiber core wires forming the optical fiber ribbon is 12 or more. 
     Preferably, a pitch between the plurality of optical fiber core wires is 200 μm or less. 
     Preferably, an outer diameter of a glass fiber of the optical fiber core wire is 110 μm or less. 
     Preferably, an outer diameter of the optical fiber core wire is 200 μm or less. 
     According to the fourth aspect of the present invention, the plurality of optical fiber core wires forming the optical fiber ribbon are dispersed by the flow of the heat-meltable member, and this can suppress a variation in transmission loss in each optical fiber core wire due to disarrangement of the optical fiber core wires. 
     The above effects are particularly remarkable when the number of the plurality of optical fiber core wires forming the optical fiber ribbon is 12 or more. Also, the above effects are remarkable when the pitch between the plurality of optical fiber core wires is 200 μm or less. Also, the above effects are remarkable when the outer diameter of the glass fiber of the optical fiber core wire is 110 μm or less. Also, the above effects are remarkable when the outer diameter of the optical fiber core wire is 200 μm or less. 
     Effects of the Invention 
     The present invention can provide a reinforcing sleeve and the like that can efficiently reinforce a spliced portion of optical fiber tapes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a side view showing a reinforcing sleeve  1 . 
         FIG. 1B  is a cross-sectional view taken along A-A line in  FIG. 1A . 
         FIG. 2A  is a view showing a reinforcing step for a spliced portion between optical fiber core wires  11  using the reinforcing sleeve  1 , and is a cross-sectional view before shrinking. 
         FIG. 2B  is a view showing the reinforcing step for the spliced portion between the optical fiber core wires  11  using the reinforcing sleeve  1 , and is a cross-sectional view in the course of shrinking. 
         FIG. 2C  is a view showing the reinforcing step for the spliced portion between the optical fiber core wires  11  using the reinforcing sleeve  1 , and is a cross-sectional view after shrinking. 
         FIG. 3A  is a view showing an optical fiber ribbon  12 . 
         FIG. 3B  is a view showing a state in which the optical fiber ribbons  12  are butted to each other. 
         FIG. 4A  is a cross-sectional view of a reinforcing sleeve  1   a.    
         FIG. 4B  is a cross-sectional view of a reinforcing sleeve  1   b.    
         FIG. 5A  is a cross-sectional view of a reinforcing sleeve  1   c  before shrinking. 
         FIG. 5B  is a cross-sectional view of the reinforcing sleeve  1   c  in the course of shrinking. 
         FIG. 6A  is a cross-sectional view of a reinforcing sleeve  1   d.    
         FIG. 6B  is a cross-sectional view of a reinforcing sleeve  1   e.    
         FIG. 7A  is a side view of a reinforcing sleeve  1   f.    
         FIG. 7B  is a cross-sectional view taken along D-D line in  FIG. 7A . 
         FIG. 7C  is a cross-sectional view taken along E-E line in  FIG. 7A . 
         FIG. 8A  is a cross-sectional view of a reinforcing sleeve  1   g.    
         FIG. 8B  is a cross-sectional view of a reinforcing sleeve  1   h.    
         FIG. 9  is a cross-sectional view of a reinforcing sleeve  1   i.    
         FIG. 10A  is a view showing a splicing step of optical fiber core wires  101  using a traditional reinforcing sleeve  100 . 
         FIG. 10B  is a view showing the splicing step of the optical fiber core wires  101  using the traditional reinforcing sleeve  100 . 
         FIG. 10C  is a view showing the splicing step of the optical fiber core wires  101  using the traditional reinforcing sleeve  100 . 
         FIG. 11A  is a view showing the reinforcing step for a spliced portion between the optical fiber core wires  101  using the traditional reinforcing sleeve  100 , and is a cross-sectional view before shrinking. 
         FIG. 11B  is a view showing the reinforcing step for the spliced portion between the optical fiber core wires  101  using the traditional reinforcing sleeve  100 , and is an ideal cross-sectional schematic view after shrinking. 
         FIG. 11C  is a view showing the reinforcing step for the spliced portion between the optical fiber core wires  101  using the traditional reinforcing sleeve  100 , and is an actual cross-sectional schematic view after shrinking. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     Hereinafter, preferable embodiments of the present invention will be described with reference to the accompanying drawings.  FIG. 1A  is a side view of a reinforcing sleeve  1 , and  FIG. 1B  is a cross-sectional view taken along A-A line in  FIG. 1A . The reinforcing sleeve  1  is a member that collectively reinforces spliced portions of a plurality of optical fiber core wires that are disposed side by side. The reinforcing sleeve  1  includes a heat-shrinkable tube  5 , a heat-meltable member  7 , a tension member  9 , and so on. 
     The heat-shrinkable tube  5  is a cylindrical member having an approximately circular cross section. The heat-shrinkable tube  5  is made of polyethylene resin, for example. 
     The heat-meltable member  7  is in a cylindrical shape having an approximately circular or elliptical cross section. The heat-meltable member  7  is made of ethylene-vinyl acetate resin, for example. The heat-meltable member  7  melts preferably at a temperature lower than a heat-shrinking temperature of the heat-shrinkable tube  5 . A thick portion  13  having a thickness that is greater than thicknesses of other parts is provided at proximity of a center portion of a width direction of the heat-meltable member  7 . The thick portion  13  is formed on a lower part of the heat-meltable member  7  (on a side of the tension member  9 ). Also, the thick portion  13  is formed so that an inner surface side of the heat-meltable member  7  is in a shape protruding toward a center of the heat-meltable member  7 . 
     The tension member  9  is a rod-shaped member. The tension member  9  is made of steel, carbon, glass, or ceramics, for example. The tension member  9  and the heat-meltable member  7  are inserted into the heat-shrinkable tube  5 . A rivet-head portion  3  is formed at a part of the heat-shrinkable tube  5  to prevent the tension member  9  and the heat-meltable member  7  from falling. 
     If the tension member  9  inclines in the cross section, the tension member  9  may shift in relation to a position of the heat-shrinkable tube  5  and this may cause the tension member  9  to lose its balance. In such a case, non-uniform force presses the optical fiber core wires against the tension member  9 , which may deteriorate an alignment of the optical fiber core wires. The rivet-head  3 , however, prevents the inclination of the tension member  9  and is effective in maintaining the arrangement of the tension member  9  and the optical fiber core wires. 
     Next, a reinforcing method for an optical fiber spliced portion using the reinforcing sleeve  1  will be described.  FIG. 2A  to  FIG. 2C  are views illustrating reinforcing steps for the spliced portion between optical fiber core wires  11  forming an optical fiber tape. First, similarly to the above-mentioned  FIG. 10A  to  FIG. 10C , outer jackets of end portions of the optical fiber core wires  11  are removed for a predetermined length, and then the end portions are butted together and fusion bonded to each other. At this time, a plurality of the optical fiber core wires  11  on one side of the optical fiber core wires are inserted into the heat-meltable member  7  of the reinforcing sleeve  1 , and the reinforcing sleeve  1  is put aside on the one side of the optical fiber core wires. 
     Next, as shown in  FIG. 2A , the reinforcing sleeve  1  is moved so as to cover the spliced portion of the plurality of optical fiber core wires  11 . At this time, the optical fiber core wires  11  are disposed along the protruding shape of the thick portion  13 , and this facilitates dispersion of the optical fiber core wires  11  in the width direction. Then, the heat-shrinkable tube  5  and the heat-meltable member  7  are heated to shrink the heat-shrinkable tube  5  and melt the heat-meltable member  7 . 
       FIG. 2B  is a cross-sectional view showing a state in which the heat-shrinkable tube  5  starts shrinking and the heat-meltable member  7  starts melting. As mentioned above, the thick portion  13  is formed at the substantially center portion of the width direction of the heat-meltable member  7 . Thus, in a cross section perpendicular to the longitudinal direction of the heat-meltable member  7 , an amount of the heat-meltable member at proximity of the center portion of the width direction of the heat-meltable member  7  is greater than an amount of the heat-meltable member at proximity of the end portions of the width direction of the heat-meltable member  7 . Thus, when the heat-meltable member  7  melts, the heat-meltable member  7  flows from the proximity of the center portion of the width direction toward the end portion sides (arrows B in the drawing). 
       FIG. 2C  is a cross-sectional view showing a state in which the heat-shrinkable tube  5  is completely shrunken. As mentioned above, the heat-meltable member  7  applies side pressure to the optical fiber core wires  11  when the heat-shrinkable tube  5  shrinks. However, when melting the heat-meltable member  7 , the optical fiber core wires  11  disperse toward the end portion sides of the width direction. For this reason, force applied by the flow of the heat-meltable member  7  pushing the optical fiber core wires  11  toward the end portion sides of the width direction counteracts the side pressure applied to each of the optical fiber core wires  11 . This can suppress floating of the optical fiber core wires  11  from the tension member  9  and prevent disarrangement. In reality, the optical fiber core wires  11  are not in contact with the tension member  9 , and the heat-meltable member  7  enters into a space between the optical fiber core wires  11  and the tension member  9 . 
     When the heat-meltable member  7  is completely melted and the heat-shrinkable tube  5  is completely shrunken, the heating is stopped to cool, and then the heat-meltable member  7  unifies the tension member  9  with the spliced portion of the optical fiber core wires  11  as one body. In this way, a reinforcing structure of the spliced portion of the optical fibers using the reinforcing sleeve  1  can be obtained. That is, in the reinforcing structure of the spliced portion of the optical fibers, the heat-meltable member  7  covers the spliced portion of the optical fiber core wires  11 , and the optical fiber core wires  11  forming the optical fiber tape are disposed along a surface of the tension member  9 . 
     If the optical fiber tape is an optical fiber ribbon, in particular, in which a plurality of optical fiber core wires are bonded at intervals in a longitudinal direction and adjacent bonded portions are arranged in a zigzag arrangement or in a step form in the longitudinal direction, for example, the arrangement of the optical fiber core wires  11  is likely to be disarranged due to the side pressure. 
       FIG. 3A  is a view showing an optical fiber ribbon  12 . As mentioned above, the optical fiber ribbon  12  includes the plurality of optical fiber core wires  11  that are arranged side by side and bonded at intervals in the longitudinal direction at bonding portions  11   c . The optical fiber core wire  11  includes a glass fiber  11   a  inside and a resin coating  11   b  that is disposed on an outer periphery of the glass fiber  11   a . The resin coating  11   b  at an end portion of the optical fiber core wire  11  is removed when splicing the optical fiber core wires  11 . Here, a pitch P between the optical fiber core wires  11  is almost equal to an outer diameter of the optical fiber core wire  11 . 
       FIG. 3B  is a schematic view showing a state in which the optical fiber ribbons  12  are butted and fusion bonded with each other. The optical fiber ribbon  12  has intermittent bonding portions for fixing the optical fiber core wires  11  with each other. Thus, the optical fiber ribbon  12  has longer independent parts of the optical fiber wires  11  than a traditional optical fiber tape, in which the optical fiber core wires  11  are fixed over an entire length thereof. For this reason, the arrangement of the optical fiber core wires  11  of the optical fiber ribbon  12  has higher degree of freedom, which may cause position shifting of the optical fiber core wires  11  (the glass fibers  11   a ) when butting the glass fibers  11   a  to each other (a section X in the drawing). Thus, the present embodiment is particularly effective for the intermittently bonded optical fiber ribbon in which the plurality of optical fiber core wires  11  are disposed side by side and bonded at intervals in the longitudinal direction. 
     Also, the disarrangement due to the side pressure is likely to occur often in a case with the optical fiber core wire  11  having the small outer diameter (the outer diameter of the resin coating  11   b ). Thus, the present embodiment is particularly effective in a case where each optical fiber core wire  11  forming the optical fiber tape has the outer diameter of 225 μm or less. It is further effective when the outer diameter of the optical fiber core wire is reduced to 200 μm or less, or even to 170 μm or less. 
     Moreover, the glass fiber  11   a  without the resin coating  11   b  traditionally has the outer diameter of 125 μm. However, if the glass fiber  11   a  is thinner, the rigidity of the optical fiber core wire  11  decreases, and this may cause the disarrangement of the glass fibers  11   a  due to the side pressure. Thus, the present embodiment is particularly effective in a case where the outer diameter of each of the glass fibers  11   a  forming the optical fiber tape is 110 μm or less. 
     Moreover, if the pitch P between the optical fiber core wires  11  is smaller than a traditional pitch of 250 μm, it is necessary to prevent the disarrangement of the optical fiber core wires  11  with certainty. Otherwise, issues such as the glass fibers  11   a  coming into contact with each other are likely to occur. Thus, the present embodiment is particularly effective in a case where the pitch P between the optical fiber core wires  11  is 225 μm or less. In particular, if the pitch P between the optical fiber core wires  11  is reduced to 200 μm or less, or even to 170 μm or less, the possibility of contact or intersection between the glass fibers  11   a  increases, and thus the present embodiment is furthermore effective. 
     Also, the more the number of the optical fiber core wires  11  forming the optical fiber tape is, the more likely the disarrangement of the optical fiber core wires  11  due to the side pressure occurs. Thus, the present embodiment is particularly effective in a case where the number of the plurality of optical fiber core wires  11  forming the optical fiber tape is 8 or more. The present embodiment is furthermore effective as the number of the optical fiber core wires is increased to 12 or more, 16 or more, or 24 or more. 
     That is, the present embodiment is remarkably effective for the intermittently bonded optical fiber ribbon having the large number of the optical fiber core wires  11 , the small pitch P between the optical fiber core wires  11 , and the small outer diameter of the optical fiber core wire  11 . 
     As above, according to the first embodiment of the present invention, the thick portion  13  is formed at the substantially center portion of the width direction of the heat-meltable member  7 . This makes the amount of the heat-meltable member at the center portion greater than the amount of the heat-meltable member on the end portion sides, and thus the flow of the heat-meltable member  7  when melted can disperse the optical fiber core wires  11  to the width direction. This can suppress the disarrangement of the optical fiber core wires  11  due to the side pressure and suppress a variation in transmission loss in each of the optical fiber core wires  11 . 
     Also, the thick portion is formed in a shape protruding toward the inner surface side of the heat-meltable member  7 . This allows the optical fiber core wires  11  to be arranged along the protruding shape of the thick portion  13 . This protruding shape also allows the optical fiber core wires  11  to be dispersed to and arranged on the end portion sides of the width direction. 
     The shape of the thick portion  13  is not limited to the protruding shape protruding toward the inner surface side of the heat-meltable member  7 . For example, the thick portion  13  may protrude toward an outer surface side of the heat-meltable member  7  (on a side of the tension member  9 ), as in a reinforcing sleeve  1   a , shown in  FIG. 4A . This can also make the amount of the heat-meltable member at the center portion greater than the amount of the heat-meltable member on the end portion sides, and thus the flow of the heat-meltable member  7  when melted can disperse the optical fiber core wires  11  to the width direction. 
     Furthermore, to make the heat-meltable member  7  flow in the width direction more efficiently, an upper surface of the tension member  9  (on a side of the heat-meltable member  7 ) may protrude toward a side of the heat-meltable member  7  as in a reinforcing sleeve  1   b  shown in  FIG. 4B . By forming a slope surface, which gradually moves away from the heat-meltable member  7  as moving toward the end portion of the width direction, on the upper surface of the tension member  9 , the heat-meltable member  7  can flow toward the end portion sides of the width direction more efficiently. Although linear slopes are formed in the example shown in the drawing, the slope may be a curved surface or may be linearly shaped. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described.  FIG. 5A  is a cross-sectional view of a reinforcing sleeve  1   c . In the descriptions hereafter, structures having the same functions as in the reinforcing sleeve  1 ,  1   a , and  1   b  will have the same notations as in  FIG. 1A  to  FIG. 4B , and redundant descriptions will be omitted. 
     The reinforcing sleeve  1   c  has approximately the same structure as the reinforcing sleeve  1  except that the heat-meltable member  7  is in a different shape. In the present embodiment, the thick portion  13  is disposed on an upper part of the heat-meltable member  7  (on a side opposite to the tension member  9 ). More particularly, the thick portion  13  is formed on the upper part of the heat-meltable member  7  in a shape protruding toward the inner surface side of the heat-meltable member  7 . That is, a lower part of the heat-meltable member  7  (the side of the tension member  9 ) is in the same shape as traditional heat-meltable members. 
       FIG. 5B  is a cross-sectional view showing a state in which the heat-shrinkable tube  5  starts shrinking and the heat-meltable member  7  starts melting. As mentioned above, the thick portion  13  is formed at the substantially center portion of the width direction of the heat-meltable member  7 . When the heat-meltable member  7  softens and melts, the heat-meltable member  7  starts to flow from the upper part to the lower part. When the heat-meltable member  7  has flowed to the lower part to a certain extent, flows to the end portions of the width direction occur (arrows C in the drawing). 
     As above, forming the thick portion  13  on the opposite side of the tension member  9  can also make the amount of the heat-meltable member at proximity of the center portion of the width direction of the heat-meltable member  7  in a cross section perpendicular to the longitudinal direction of the heat-meltable member  7  greater than the amount of the heat-meltable member on proximity of the end portions of the width direction. 
     The thick portion  13  may be formed on the upper part of the heat-meltable member  7  (the opposite side of the tension member  9 ) in a shape protruding toward an outer surface side of the heat-meltable member  7  as in a reinforcing sleeve  1   d  shown in  FIG. 6A . In addition, the upper surface side of the tension member  9  (the side of the heat-meltable member  7 ) may be in a shape protruding upward as in a reinforcing sleeve  1   e  shown in  FIG. 6B . 
     According to the second embodiment of the present invention, the same effects as in the first embodiment can be obtained. As above, the thick portion  13  may be either on the lower part or on the upper part of the heat-meltable member  7 . 
     Third Embodiment 
     Next, a third embodiment will be described.  FIG. 7A  is a side view of a reinforcing sleeve  1   f ,  FIG. 7B  is a cross-sectional view taken along D-D line in  FIG. 7A , and  FIG. 7C  is a cross-sectional view taken along E-E line in  FIG. 7A . The reinforcing sleeve if has approximately the same structure as the reinforcing sleeve  1  except that both the heat-meltable member  7  and a heat-meltable member  17  are used. In the present embodiment, the heat-meltable member includes the tube-shaped heat-meltable member  7 , which is a first heat-meltable member, and the heat-meltable member  17 , which is a second heat-meltable member disposed at the center portion of the width direction of the heat-meltable member  7 . 
     The heat-meltable member  17  is disposed between the heat-meltable member  7  and the tension member  9 . That is, the heat-meltable member  17  is disposed on the lower part of the heat-meltable member  7 . Also, the heat-meltable member  17  is in a rod shape and is in an elliptical shape, for example. That is, an outer shape of the heat-meltable member  17  is formed to be protruding toward the heat-meltable member  7 . Note that cross sectional shape of the heat-meltable member  17  is not particularly limited. 
     A width of the heat-meltable member  17  is smaller than a width of the heat-meltable member  7 . With the heat-meltable member  17  being disposed at the substantially center portion of the width direction, it is also possible to make the amount of the heat-meltable member (sum of the heat-meltable member  7  and the heat-meltable member  17 ) at proximity of the center portion of the width direction of the heat-meltable member  7  in a cross section perpendicular to the longitudinal direction of the heat-meltable member  7  greater than the amount of the heat-meltable member (the heat-meltable member  7  only) on proximity of the end portions of the width direction. 
     The heat-meltable member  17  may be disposed over an entire length of the reinforcing sleeve  1   f , or may be disposed only over a predetermined range at substantially center of a longitudinal direction of the reinforcing sleeve  1   f . As mentioned above, the glass fibers are exposed at the spliced portion of the optical fiber core wires  11 . At the exposed part of the glass fiber, a fiber diameter is small and the resin coating, which is a protective layer, is removed. Thus, the exposed part is likely to be affected by the side pressure. 
     Thus, with the heat-meltable member  17  disposed at a part corresponding to the exposed part of the glass fiber, the flow of the heat-meltable members  7  and  17  when melted, as mentioned above, can suppress the influence of the side pressure. Also, the amount of use of the heat-meltable members can be saved by not disposing the heat-meltable member  17  at proximity of end portions of the longitudinal direction of the reinforcing sleeve  1   f , since such the portions have the resin coating and are less affected by the side pressure compared to the glass fiber exposed portion. 
     A position of the heat-meltable member  17  is not restricted to a position between the heat-meltable member  7  and the tension member  9 . For example, the heat-meltable member  17  may be disposed inside the heat-meltable member  7  as in a reinforcing sleeve  1   g  shown in  FIG. 8A . In such the case, the optical fiber core wires  11  may be disposed on an upper part of the heat-meltable member  17  or on a lower part of the heat-meltable member  17 . 
     Alternatively, the heat-meltable member  17  may be disposed on the upper part of the heat-meltable member  7  (on the side opposite to the tension member  9 ) as in a reinforcing sleeve  1   h  shown in  FIG. 8B . Furthermore, although drawings are omitted, the upper surface of the tension member  9  may be in a shape protruding toward the heat-meltable members  7  and  17  as mentioned above. 
     According to the third embodiment, the same effects as in the first embodiment can be obtained. As above, a plurality of the heat-meltable members  7  and  17  may be used to increase the amount of the heat-meltable member at the center portion of the width direction. 
     Fourth Embodiment 
     Next, a fourth embodiment will be described.  FIG. 9  is a cross-sectional view of a reinforcing sleeve  1   i . The reinforcing sleeve  1   i  has approximately the same structure as the reinforcing sleeve  1  except that, instead of forming the thick portion  13 , the shape of the heat-meltable member  7  is altered. That is, although the tube-shaped heat-meltable member  7  has a substantially uniform thickness over an entire circumference, a convex portion  14  protruding toward an inner surface side is formed at proximity of a center portion of a width direction on the side of the tension member  9 . 
     It is expected that molding the heat-meltable member  7  in advance to form the convex portion  14  protruding toward the inner surface side as above can provide the same effects as the reinforcing sleeve  1   b , for example. In addition, as the convex portion  14  is formed, a concave portion is formed on an outer surface at the center of the width direction on the side of the tension member  9 . This facilitates positioning of the heat-meltable member  7  in a rotational direction. Furthermore, when using the heat-meltable member  17  as in the reinforcing sleeve  1   f , positioning of the heat-meltable member  17  is easy since the heat-meltable member  17  can be disposed to fit the concave portion that is formed in advance on the outer surface. 
     According to the fourth embodiment, the same effects as in the first embodiment can also be obtained. That is, the present invention is to have a structure in which the heat-meltable member can disperse the optical fiber core wires from proximity of the center portion toward proximity of the end portions of the width direction. For example, the convex portion  14  protruding toward the inner surface side may be provided by molding the inner surface shape at the proximity of the center of the width direction of the heat-meltable member  7  on the side of the tension member. Alternatively, a thick portion  8  having a thickness larger than the other parts may be formed at proximity of the center portion of the width direction of the heat-meltable member  7  so as to function as the convex portion  14 . Further alternatively, the heat-meltable member  17 , which is the second heat-meltable member, may be disposed at proximity of the substantially center of the width direction of the heat-meltable member  7  so as to function as the convex portion  14 . Needless to say, structures in the each of the embodiments can be combined with each other. 
     Although the preferred embodiments of the present invention have been described referring to the attached drawings, the technical scope of the present invention is not limited to the embodiments described above. It is obvious that persons skilled in the art can think out various examples of changes or modifications within the scope of the technical idea disclosed in the claims, and it will be understood that they naturally belong to the technical scope of the present invention. 
     DESCRIPTION OF NOTATIONS 
     
         
           1 ,  1   a ,  1   b ,  1   c ,  1   d ,  1   e ,  1   f ,  1   g ,  1   h ,  1   i  . . . reinforcing sleeve 
           3  . . . rivet-head portion 
           5  . . . heat-shrinkable tube 
           7 , 17  . . . heat-meltable member 
           9  . . . tension member 
           11  . . . optical fiber core wire 
           11   a  . . . glass fiber 
           11   b  . . . resin coating 
           11   c  . . . bonding portion 
           12  . . . optical fiber ribbon 
           13  . . . thick portion 
           14  . . . convex portion 
           100  . . . reinforcing sleeve 
           101  . . . optical fiber core wire 
           103  . . . electrode 
           105  . . . heat-shrinkable tube 
           107  . . . heat-meltable member 
           109  . . . tension member