Optical fiber unit and optical fiber cable

An optical fiber unit includes: an optical fiber bundle formed by bundling a plurality of optical fibers; and a plurality of bundling members. Each of the bundling members is wound on an outer circumference of the optical fiber bundle along a length direction of the optical fiber bundle while a winding direction of the bundling member is reversed alternately, and joined with another bundling member at reverse sections where the winding direction of the bundling member is reversed. A region surrounded by a pair of the bundling members to be joined at the reverse sections includes a joining point at one of the reverse sections of another pair of the bundling members.

TECHNICAL FIELD

One or more embodiments of the present invention relate to an optical fiber unit and an optical fiber cable.

BACKGROUND

Techniques are known for forming an optical fiber cable including optical fiber units which are optical fiber aggregates formed by bundling a plurality of optical fibers. In such techniques, it is common to employ a method wherein a rough winding string (bundling member) is wound around the bundle of optical fibers to thereby suppress/prevent the bundle of optical fibers from falling apart while allowing the optical fiber units to be differentiated from one another by the colors of the bundling members.

In relation to such bundling members, Patent Literature 1 discloses a technique in which a plurality of bundling members are wound helically around a bundle of optical fibers and the bundling members are joined together, to thereby tie the bundle of optical fibers together. Patent Literature 2 (particularly FIG. 7 of Patent Literature 2) discloses a technique wherein the circumference of a bundle of a plurality of optical fibers is bundled with two bundling members by winding the two bundling members in an S-Z configuration, and the two bundling members are bonded and fixed together at reverse sections where their winding directions are reversed.

CITATION LIST

Patent Literature

SUMMARY

In Patent Literature 1, a plurality of bundling members are wound helically on the circumference of a bundle of optical fibers, and the bundling members are joined together at their intersection points. Thus, in performing mid-span branching for extracting a specific optical fiber, the joined sections between the bundling members need to be disengaged. At that time, the bundling members need to be retrieved helically, which increases the time and effort for extracting the optical fiber. Also, at the time of retrieving the bundling members, there is a possibility that the optical fibers may break as a result of e.g. the worker's finger getting caught in the optical fibers.

In contrast, a configuration wherein two bundling members are wound in an S-Z configuration around the circumference of the bundle of optical fibers, as in Patent Literature 2, is advantageous in that workability at the time of extracting optical fibers is improved. If, however, there is a defect in the joining of bundling members at reverse sections where their winding directions are reversed, the optical fibers cannot be kept bundled.

One or more embodiments of the present invention may enable the retaining of the bundle of optical fibers even if there is a defect in the joining of bundling members at reverse sections where their winding directions are reversed.

One or more embodiments of the present invention provide an optical fiber unit including: an optical fiber bundle formed by bundling a plurality of optical fibers; and a plurality of bundling members. Each of the bundling members is wound on an outer circumference of the optical fiber bundle along a length direction of the optical fiber bundle while its winding direction is reversed alternately, and joined with another bundling member at reverse sections where its winding direction is reversed. A region surrounded by a pair of the bundling members to be joined at the reverse sections includes a joining point at one of the reverse sections of another pair of the bundling members.

Other features of one or more embodiments of the present invention are made clear by the following description and the drawings.

Advantageous Effects

With one or more embodiments of the present invention, it may be possible to retain the bundle of optical fibers even if there is a defect in the joining of bundling members at reverse sections where their winding directions are reversed.

DETAILED DESCRIPTION

At least the following matters are made clear from the following description and the drawings.

According to one or more embodiments, an optical fiber unit includes: an optical fiber bundle formed by bundling a plurality of optical fibers; and a plurality of bundling members. Each of the bundling members is wound on an outer circumference of the optical fiber bundle along a length direction of the optical fiber bundle while its winding direction is reversed alternately, and joined with another bundling member at reverse sections where its winding direction is reversed. A region surrounded by a pair of the bundling members to be joined at the reverse sections includes a joining point at one of the reverse sections of another pair of the bundling members. With this optical fiber unit, even if the joining of the bundling members at the reverse sections where their winding directions are reversed is faulty, it is possible to retain the bundle of the optical fibers.

In one or more embodiments, one pair of the bundling members is wound around the entire circumference of the optical fiber bundle; and another pair of the bundling members is wound around the entire circumference of the optical fiber bundle. In this way, even if the joining points of one of the pairs of bundling members are consecutively faulty, the other of the pairs of bundling members can retain the bundle of the optical fibers.

In one or more embodiments, the bundling member is joined with said another bundling member at the reverse sections, and is also joined with a different bundling member from said another bundling member at intersection points between said different bundling member and the bundling member. In this way, the joining of the bundling members is strengthened.

In one or more embodiments, a joining point at one of the reverse sections of one pair of the bundling members and another joining point which is at one of the reverse sections of a different pair of the bundling members and which is in a region surrounded by said one pair of the bundling members joined at said joining point are arranged along the length direction of the optical fiber bundle. In this way, the joining points are easy to separate.

In one or more embodiments, the aforementioned region includes a plurality of joining points at the reverse sections of other pairs of the bundling members. In this way, the joining of the bundling members is strengthened.

Further, according to one or more embodiments, an optical fiber cable includes: a plurality of optical fiber units; and an outer sheath that covers the plurality of optical fiber units. Each of the optical fiber units includes an optical fiber bundle formed by bundling a plurality of optical fibers, and a plurality of bundling members. Each of the bundling members is wound on an outer circumference of the optical fiber bundle along a length direction of the optical fiber bundle while its winding direction is reversed alternately, and joined with another bundling member at reverse sections where its winding direction is reversed. A region surrounded by a pair of the bundling members to be joined at the reverse sections includes a joining point at one of the reverse sections of another pair of the bundling members. In this way, even if the joining of the bundling members at the reverse sections where their winding directions are reversed is faulty, it is possible to retain the bundle of the optical fibers.

First Embodiment

Structure of Optical Fiber Unit2, Etc.:

FIG. 1Ais a cross-sectional view of an optical fiber cable1including optical fiber units2. The optical fiber cable1includes: a plurality of optical fiber units2; and an outer sheath3. Each optical fiber unit2has a structure wherein a plurality of optical fibers8are bundled by bundling members10. The structure of the optical fiber unit2is described in detail further below. In this example, the optical fiber cable1includes three optical fiber units2. The three optical fiber units2are covered by a wrapping tape5, and the outer side thereof is covered by the outer sheath3. Tension members4A and rip cords4B are embedded in the outer sheath3.

FIG. 1Bis a perspective view of the optical fiber unit2according to the first embodiment. The optical fiber unit2has a structure wherein a bundle of a plurality of optical fibers8(i.e., an optical fiber bundle6) is bundled by bundling members10. The bundling members10are wound on the outer circumference of the optical fiber bundle6, and thus, the plurality of optical fibers8are bundled together and are prevented from falling apart. In this example, the optical fiber bundle6is constituted by bundling together a plurality of intermittently connected optical fiber ribbons7.

FIG. 2is a diagram illustrating an example of an intermittently connected optical fiber ribbon7.

The intermittently connected optical fiber ribbon7is an optical fiber ribbon7including a plurality of optical fibers (twelve in this example) arranged side by side and connected intermittently. Two adjacent ones of the optical fibers8are connected by a connection part9A. Between two adjacent optical fibers8, a plurality of connection parts9A are arranged intermittently in the length direction. The plurality of connection parts9A of the intermittently connected optical fiber ribbon7are arranged intermittently and two-dimensionally in the length direction and the ribbon's width direction. Regions other than the connection parts9A between the two adjacent optical fibers8constitute non-connected parts9B. In the non-connected parts9B, the two adjacent optical fibers8are not restrained. Thus, the intermittently connected optical fiber ribbon7can be rolled up into a cylindrical form (a bundle), or folded up, and the multitude of optical fibers8can be bundled with high density.

It should be noted that the intermittently connected optical fiber ribbon7constituting the optical fiber bundle6is not limited to the example illustrated in the figure. For example, the arrangement of the connection parts9A may be changed. Also, the number of optical fibers8constituting the intermittently connected optical fiber ribbon7may be changed. Further, the optical fiber bundle6does not have to be constituted by an intermittently connected optical fiber ribbon7, but may instead be constituted by, for example, bundling a plurality of separate optical fibers8.

The bundling member10is a member that bundles the plurality of optical fibers8together. The bundling member10is a thread-form, cord-form, or tape-form member capable of tying the plurality of optical fibers8together. Each bundling member10is wound on the outer circumference of the optical fiber bundle6. In the illustrated optical fiber unit2, the optical fiber bundle6is bundled by four bundling members10, but there may be four or more bundling members10in the optical fiber unit2, as will be described further below. In the description below, the bundling members10may be indicated with indexes (A to D) so that the bundling members10are distinguished from one another for explanation.

A predetermined color is applied to each bundling member10, and thus, the bundling member also functions as an identification member. The bundling members10in each optical fiber unit2have different colors, and can thus be differentiated from one another. In cases where each optical fiber unit2includes two bundling members10as illustrated in the figures, it is also possible to differentiate the optical fiber units2from one another by the combination of colors of the bundling members10. Instead of coloring the bundling members10, an identification mark may be printed on the surface of each bundling member10.

FIG. 3is a diagram illustrating a cross-sectional structure of the bundling member10. The bundling member10includes core parts11and a cover part12. The core parts11are members that extend along the length direction of the optical fiber unit2, and the bundling member10includes a plurality of the core parts11. The cover part12is a member that covers the outer circumference of each of the core parts11, and that has a lower melting point than the melting point of the core parts11. The two bundling members10which bundle the optical fiber unit2are thermally fusion-bonded at intersection points therebetween by the adhesiveness that arises by heating the cover part12at a temperature equal to or higher than the melting point. In one or more embodiments, the difference between the melting point of the core part11and the melting point of the cover part12is 20° C. or greater. The melting point of the core part11may be from 200 to 230° C., and the melting point of the cover part12may be from 150 to 180° C. It is possible that: even when the cover part12is heated and molten, the cover part12either does not bond with the optical fibers8or has a weak adhesive force even if it bonds with the optical fibers; and the cover part does not cause degradation of the cover layer(s) of the optical fibers8.

As for the core parts11and the cover part12, it is possible to use, for example, a high melting point resin such as polypropylene (PP), polyamide (PA) or polyethylene terephthalate (PET), or a high melting point fiber such as polypropylene fiber, polyamide fiber (e.g. nylon (registered trademark)) or polyester fiber (e.g. PET fiber), or a high melting point tape or film made of e.g. PET or PP, covered by: a thermoplastic resin which is capable of reversibly repeating softening and hardening by heating and cooling, e.g. a low melting point resin such as polyethylene (PE), ethylene-vinyl acetate copolymer (EVA) or ethylene-ethyl acrylate copolymer (EEA); or a so-called hot-melt adhesive which employs a thermoplastic resin or rubber as a base and which is capable of reversibly repeating softening and hardening by heating and cooling.

It should be noted that the bundling members10do not have to be a composite material of a high melting point material (core parts11) and a low melting point material (cover part12) as illustrated inFIG. 3, and instead may be constituted by a single material. For example, each bundling member may be constituted by either a high melting point material or a low melting point material; also, the two bundling members10may be constituted by different materials.

The width of the bundling member10is, in one or more embodiments, from 1 mm to 2 mm inclusive. If the width of the bundling member10is narrower than 1 mm, the bundling member may break at the time of fusion-bonding. If the width of the bundling member10is wider than 2 mm, heat may not be transferred sufficiently, making fusion-bonding difficult. In the present embodiment, a bundling member10having a width of from 1.8 to 1.9 mm (thickness: 0.1 mm) is used.

FIG. 4is an explanatory diagram for illustrating how the bundling members10are wound.FIG. 5Ais a developed view of the bundling members10for illustrating how the bundling members10are wound. InFIG. 5A, a position on the outer circumferential surface of the optical fiber bundle6is illustrated in a cylindrical coordinate system on the assumption that the outer circumferential surface of the optical fiber bundle6is a circumferential surface. Accordingly, the horizontal axis in FIG.5A indicates a position in the length direction. Further, the vertical axis therein indicates an angle from a reference position (0 degrees) and indicates a position in the circumferential direction on the outer circumferential surface of the optical fiber bundle6. How the bundling members10are wound around the optical fiber bundle6is described below also with reference toFIG. 1B.

Each bundling member10is wound on the outer circumference of the optical fiber bundle6and is arranged along the length direction of the optical fiber unit2such that the bundling member depicts an arc covering half the circumference of the bundle (i.e., 180 degrees). The bundling member10is joined (fusion-bonded) with another bundling member10at a joining point15. Further, the winding direction, with respect to the optical fiber bundle6, of the bundling member10is reversed at the joining point15(fusion-bonded point) with another bundling member10. In this way, the bundling members10are wound around the optical fiber bundle6in an S-Z configuration. In the description below, the joining point15between a bundling member10A and a bundling member10D is indicated with an index AD while the joining point15between a bundling member10B and a bundling member10C is indicated with an index BC, so that the joining points15may be distinguished from one another for explanation.

Each bundling member10is wound on the outer circumference of the optical fiber bundle6along the length direction of the optical fiber bundle6while the winding direction of the bundling member10is reversed alternately. Each bundling member10is joined with another bundling member10at reverse sections where their winding directions are reversed. In this way, if the joining points at the reverse sections are separated, the bundling members10covering the outer circumference of the optical fiber bundle6in a mesh pattern can be opened and the optical fiber(s)8can be extracted from the optical fiber unit2. If the bundling members10are wound helically in one direction on the outer circumference of the optical fiber bundle6, it is necessary to helically retrieve or cut the bundling members10, thus increasing the time and effort for extracting the optical fiber(s)8. Stated differently, if the bundling members10are wound helically in one direction, it takes time to unwind the helically-wound bundling members10. In contrast, in the present embodiment, the optical fiber(s)8can be extracted by simply disengaging the joining point15at the time of, for example, mid-span branching, thus facilitating the extraction work. Stated differently, in the optical fiber unit2wherein the bundling members10are wound in the S-Z configuration, a worker can easily separate the bundling members10by pulling them at the terminal, and thus, the time required for work can be shortened compared to cases where the bundling members10are wound helically in one direction.

It may be that the joining strength at the joining point15is of a degree at which the joining point15is not ruptured unexpectedly but can be separated easily with the worker's hands. It may be that the force necessary for separating the joining point15between the bundling members10is smaller than the force required for cutting the bundling member10, and so, the joining strength of the bundling members10may be less than or equal to the breaking strength of each bundling member10. Further, it may be that the two bundling members10can be re-joined by applying heat with a heater or by applying an adhesive after the extraction of the optical fiber(s)8in the mid-span branching.

As illustrated inFIG. 4, when the optical fiber unit2is viewed from one side in the length direction, the joining points15are arranged so as to sandwich the optical fiber bundle6. For the sake of explanation, it is assumed that one of the joining points15is positioned at the reference position (0 degrees), and that the other joining point is positioned at 180 degrees. In the first embodiment, joining points15AD and joining points15BC are located at the reference position and the position at 180 degrees.

First, a description will be given below of how the bundling member10A and the bundling member10D among the four bundling members10are wound. The bundling member10A is wound clockwise on the outer circumference of the optical fiber bundle6(cf. upper diagram ofFIG. 4), and is joined with the bundling member10D at a joining point15AD (cf. upper diagram ofFIG. 4); then, its winding direction is reversed, and the bundling member10A is then wound counter-clockwise on the outer circumference of the optical fiber bundle6(cf. center diagram ofFIG. 4), is joined with the bundling member D at a joining point15AD (cf. center diagram ofFIG. 4), and then is again wound clockwise on the outer circumference of the optical fiber bundle6(cf. lower diagram ofFIG. 4(or upper diagramFIG. 4)); and the aforementioned steps are repeated. The bundling member10D is wound counter-clockwise on the outer circumference of the optical fiber bundle6(cf. upper diagram ofFIG. 4), and is joined with the bundling member10A at the joining point15AD (cf. upper diagram ofFIG. 4); then, its winding direction is reversed, and the bundling member10D is then wound clockwise on the outer circumference of the optical fiber bundle6(cf. center diagram ofFIG. 4), is joined with the bundling member10A at the joining point15AD (cf. center diagram ofFIG. 4), and then is again wound counter-clockwise on the outer circumference of the optical fiber bundle6(cf. lower diagram ofFIG. 4(or upper diagram ofFIG. 4)); and the aforementioned steps are repeated. In this way, the bundling member10A and the bundling member10D are wound with respect to the optical fiber bundle6in the S-Z configuration, as illustrated inFIG. 1B. Further, as illustrated inFIG. 4, when the optical fiber unit2is viewed from one side in the length direction, the two joining points15AD are arranged so as to sandwich the optical fiber bundle (the joining points15AD are arranged at the positions at 0 degrees and 180 degrees).

Similarly, the bundling member10B and the bundling member10C are wound with respect to the optical fiber bundle6in the S-Z configuration, as illustrated inFIG. 1B. Further, as illustrated inFIG. 4, when the optical fiber unit2is viewed from one side in the length direction, the two joining points15BC are arranged so as to sandwich the optical fiber bundle6(the joining points15BC are arranged at the positions at 0 degrees and 180 degrees).

There are two pairs of bundling members10(a pair of the bundling member10A and the bundling member10D and a pair of the bundling member10B and the bundling member10C) whose winding directions are reversed at the joining points15. The phase of one of the pairs of the bundling members10(for example, the bundling member10A and the bundling member10D) is shifted from that of the other pair of the bundling members10(for example, the bundling member10B and the bundling member10C) by 180 degrees (cf.FIG. 5A). Thus, the position of the joining point15(for example, the joining point15AD) of one of the pairs of the bundling members10is shifted in the length direction from that of the joining point (for example, the joining point15BC) of the other pair of the bundling members10.

Further, the bundling member10A and the bundling member10B are both wound on the outer circumference of the optical fiber bundle6within a range from the reference position (0 degrees) to 180 degrees. At the same time, the phase of the bundling member10A is shifted from that of the bundling member10B by 180 degrees (cf.FIG. 5A). For this reason, there are intersection points between the bundling member10A and the bundling member10B at positions at approximately 90 degrees.

Similarly, the bundling member10C and the bundling member10D are both wound on the outer circumference of the optical fiber bundle within a range from 180 degrees to 360 degrees (0 degrees). At the same time, the phase of the bundling member10C is shifted from that of the bundling member10D by 180 degrees (cf.FIG. 5A). For this reason, there are intersection points between the bundling member10C and the bundling member10D at positions at approximately 270 degrees.

InFIG. 5A, the joined sections15between the bundling members10are only at the reverse sections where their winding directions with respect to the optical fiber bundle6are reversed, but the joined sections between the bundling members10are not limited thereto.FIG. 5Bis a developed view illustrating joining points in a modified example. As illustrated inFIG. 5B, each of the bundling members10may not only be joined at the reverse sections where its winding direction with respect to the optical fiber bundle6is reversed, but may also be joined with the other bundling member10at the intersection points where the bundling member10and the other bundling member10intersect. For example, the bundling member10A is not only joined with the bundling member10D at the reverse sections where their winding directions with respect to the optical fiber bundle6are reversed, but also joined with the bundling member10B at the intersection points where the bundling member10A and the bundling member10B intersect.

FIG. 12Ais a perspective view of an optical fiber unit2according to a comparative example. Also in the comparative example, the winding direction, with respect to an optical fiber bundle6, of each S-Z-wound bundling member10is reversed at joining points15with another bundling member10.

FIG. 12Bis a developed view of the bundling members10for illustrating how the bundling members10are wound according to the comparative example. InFIG. 12B, a region surrounded by a bundling member10B and a bundling member10C corresponding to one pitch is cross-hatched. In other words, one mesh cell formed of the pair of bundling members10(the bundling member10B and the bundling member10C) joined at joining points15BC is cross-hatched. In the comparative example, as illustrated in the figure, the cross-hatched region includes no joining point of any other bundling member10(a bundling member10A or a bundling member10D).

Further, in the comparative example, a range on the outer circumferential surface of the optical fiber bundle6occupied by one bundling member10does not include another bundling member10. For example, the range from 90 degrees to 180 degrees on the outer circumferential surface of the optical fiber bundle6occupied by the bundling member10B does not include any other bundling member10.

FIG. 12Cis a developed view of the bundling members when some of the joining points15are faulty in the comparative example. This drawing illustrates the developed view of the bundling members10when the joining points15BC of the bundling member10B are faulty. For example, if an abnormality occurs in the bundling member10B when the optical fiber unit2is produced, or if an abnormal tension is applied to the bundling member10B after the optical fiber unit2is produced, the joining points15BC may not be formed or the joining points15BC may be ruptured, thereby causing the joining points15BC to be consecutively faulty, as illustrated inFIG. 12C. If the joining points15BC are consecutively faulty, the bundling member10B and the bundling member10C are separated.

In the comparative example, if the joining points15BC of the bundling member10B are consecutively faulty, the mesh of the bundling members10that covers the outer circumference of the optical fiber bundle6breaks, resulting in a state where the optical fiber bundle6cannot be bundled. Hence, in the comparative example, when some of the joining points of the bundling member10are faulty, the plurality of optical fibers constituting the optical fiber bundle6may fall apart.

FIG. 6Aillustrates a region surrounded by a pair of bundling members10joined at the reverse sections according to the present embodiment. In the figure, the cross-hatching indicates a region surrounded by the bundling member10A and the bundling member10D between a joining point15AD at a reverse section where their winding directions are reversed in a predetermined direction and a joining point15AD at the next reverse section where their winding directions are reversed in the same direction. Stated differently, the region surrounded by the bundling member10A and the bundling member10D corresponding to one pitch is cross-hatched. In other words, one mesh cell formed of the pair of bundling members10(the bundling member10A and the bundling member10D) joined at the joining points15AD is cross-hatched.

In the present embodiment, the cross-hatched region includes a joining point15BC at a reverse section of another pair of bundling members10(the bundling member10B and the bundling member10C). That is, in the present embodiment, a region surrounded by a pair of bundling members10(the bundling member10A and the bundling member10D in this example) to be joined at the reverse sections—where their winding directions are reversed in the predetermined direction—includes a joining point15at a reverse section of another pair of bundling members10(the bundling member10B and the bundling member10C in this example).

FIG. 6Bis a developed view of the bundling members10when some of the joining points15AD are faulty. Also in the present embodiment, if the joining points15AD are consecutively faulty, the bundling member10A and the bundling member10D are separated.

In the present embodiment, however, the cross-hatched region includes the joining point15BC, as illustrated inFIG. 6A. With this configuration, even if the joining points15AD are consecutively faulty, the joining point15BC (joining point in the cross-hatched region) prevents the mesh of the bundling members10, which covers the outer circumference of the optical fiber bundle6, from breaking and opening up. Therefore, in the present embodiment, even if the joining points15AD are consecutively faulty, it is possible to keep the state where the optical fiber bundle6is bundled by the bundling members10.

In the present embodiment, a range on the outer circumferential surface of the optical fiber bundle6occupied by one bundling member10includes another bundling member10. For example, as illustrated inFIG. 6A, the range from 0 degrees to 180 degrees on the outer circumferential surface of the optical fiber bundle6occupied by the bundling member10A includes another bundling member10B. In other words, in the present embodiment, the range on the outer circumferential surface of the optical fiber bundle6occupied by the one bundling member10overlaps the range on the outer circumferential surface of the optical fiber bundle6occupied by another bundling member10. With this configuration, as illustrated inFIG. 6C, even if the joining points15AD are consecutively faulty and thereby the bundling member10A cannot perform the function of bundling the optical fiber bundle6, the other bundling member10B prevents the mesh of the bundling members10, which covers the outer circumference of the optical fiber bundle6, from breaking and opening up.

Further, in the present embodiment, there are two pairs of bundling members10whose winding directions are reversed at the joining points15. One of the pairs of bundling members10is wound around the entire circumference of the optical fiber bundle6, and also, the other pair of bundling members10is wound around the entire circumference of the optical fiber bundle6. More specifically, the pair of bundling members10consisting of the bundling member10A and the bundling member10D is wound around the entire circumference of the optical fiber bundle6, and also, the pair of bundling members10consisting of the bundling member10B and the bundling member10C is wound around the entire circumference of the optical fiber bundle6. With this configuration, even if the joining points15(for example, the bundling members15AD) of one of the pairs of bundling members10(for example, the bundling member10A and the bundling member10D) are consecutively faulty, the other pair of bundling members10(for example, the bundling member10B and the bundling member10C) can keep the state where the optical fiber bundle6is bundled.

Further, as illustrated inFIG. 5B, the bundling member10A may not only be joined with the bundling member10D (corresponding to “another bundling member”) at the reverse sections where the winding direction of the bundling member10A with respect to the optical fiber bundle6is reversed, but may also be joined with the bundling member10B (corresponding to a “different bundling member from said another bundling member”) at the intersection points between the bundling member10B and the bundling member10A. In this manner, each bundling member10is not only joined at the reverse sections where its winding direction with respect to the optical fiber bundle6is reversed, but also joined at intersection points where the bundling member10and another bundling member10intersect, thereby strengthening the joining of the bundling members10. This makes it easier to keep the state where the optical fiber bundle6is bundled.

At the time of mid-span branching of the optical fiber cable1in the present embodiment, a worker separates one joining point15(for example, the joining point15AD) with the worker's hands, and the worker then separates the joining point (for example, the joining point15BC) of another pair of bundling members10which is in the region surrounded by the pair of bundling members10joined at the one joining point15. In other words, after separating one joining point15(for example, the joining point15AD) with the worker's hands, the worker separates another joining point (for example, the joining point15BC) in the mesh cell formed of the pair of bundling members10joined at the one joining point15. In this way, the bundling members10covering the outer circumference of the optical fiber bundle6in a mesh pattern can be opened, and the optical fiber(s)8can be extracted. Also, when the worker repeats the separation work, the bundling members10covering the outer circumference of the optical fiber bundle6in a mesh pattern can be opened along the length direction.

According to the optical fiber unit in the present embodiment, the joining points15to be separated at the time of branching are arranged along the length direction. In other words, one joining point15(for example, the joining point15AD) and another joining point15(for example, the joining point15BC) which is of a different pair of bundling members10and which is in the region (the cross-hatched region ofFIG. 5A) surrounded by the pair of bundling members10joined at the one joining point15are arranged along the length direction. Accordingly, after separating a discretionary joining point15, the worker can sequentially separate the joining points15adjacent to the separated joining point15in the length direction with the separated joining point15as a starting point. Thus, it is easier to locate the joining points15to separate.

Method for Producing Optical Fiber Unit2:

Hereinafter, a method for producing an optical fiber unit2including four bundling members10joined as illustrated inFIG. 5Bis described.

FIG. 7is a diagram schematically illustrating a production device20for producing an optical fiber unit2.FIG. 8Ais a perspective view in the vicinity of an inlet of a bundling member passage part41(first bundling member passage parts41A and second bundling member passage parts41B) provided to a rotating member40.FIG. 8Bis a perspective view in the vicinity of an outlet of the bundling member passage part41. In the description below, the direction in which the optical fiber bundle6is fed is referred to as a “feeding direction”. In the figure, the direction from left to right is the feeding direction.

The production device20is a production device for producing the optical fiber unit2by winding the bundling members10(in this example, four bundling members10) on the outer circumference of an optical fiber bundle6formed by bundling a plurality of optical fibers8. The production device20includes a fiber passage pipe30, a rotating member40(a first rotating member40A and a second rotating member40B), and a heating unit50.

The fiber passage pipe30is a fiber passage member for feeding the optical fiber bundle6in the feeding direction. The fiber passage pipe30is a circular-cylindrical (tubular) member. The optical fiber bundle6enters the fiber passage pipe30from an opening (inlet) on the upstream side in the feeding direction, passes through the fiber passage pipe30, and is fed in the feeding direction from an opening (outlet) on the downstream side in the feeding direction. The heating unit50is arranged downstream from the fiber passage pipe30. The optical fiber bundle6that has passed through the fiber passage pipe30is immediately fed into the heating unit50.

The rotating member40is a rotating element that is arranged to the outer circumference of the fiber passage pipe30and that feeds the bundling members10while oscillating, with the feeding direction serving as the axis. The rotating member40includes a first rotating member40A and a second rotating member40B. The first rotating member40A is a circular-cylindrical member that is arranged to the outer circumference of the fiber passage pipe30(fiber passage member). The second rotating member40B is a circular-cylindrical member that is arranged to the outer circumference of the first rotating member40A. The first rotating member40A and the second rotating member40B oscillate while rotating in opposite directions from one another.

The first rotating member40A is provided rotatably with respect to the fiber passage pipe30(fiber passage member). The first rotating member40A has two first bundling member passage parts41A. The two first bundling member passage parts41A are arranged at symmetrical positions so as to sandwich the fiber passage pipe30. When the first rotating member40A rotates, with the feeding direction serving as the axis, the first bundling member passage parts41A move so as to depict an arc on the outer circumference of the optical fiber bundle6(the optical fiber bundle6passing through the fiber passage pipe30), with the feeding direction serving as the axis. The first rotating member40A is constituted by a first guide pipe42A and a first retaining pipe43A. Two first guide grooves421A are formed in the first guide pipe42A along the length direction. The first guide grooves421A are covered by the first retaining pipe43A to form the first bundling member passage parts41A. When the first rotating member40A rotates, with the feeding direction serving as the axis, the two bundling member passage parts41A move so as to depict an arc on the outer circumference of the optical fiber bundle6, with the feeding direction serving as the axis.

The second rotating member40B is provided rotatably with respect to the first rotating member40A. The second rotating member40B has two second bundling member passage parts41B. The two second bundling member passage parts41B are arranged at symmetrical positions so as to sandwich the fiber passage pipe30. When the second rotating member40B rotates, with the feeding direction serving as the axis, the second bundling member passage parts41B move so as to depict an arc on the outer circumference of the optical fiber bundle6, with the feeding direction serving as the axis. The second rotating member40B is constituted by a second guide pipe42B and a second retaining pipe43B. Two second guide grooves421B are formed in the second guide pipe42B along the length direction. The second guide grooves421B are covered by the second retaining pipe43B to form the second bundling member passage parts41B. When the second rotating member40B rotates, with the feeding direction serving as the axis, the two second bundling member passage parts41B move so as to depict an arc on the outer circumference of the optical fiber bundle6, with the feeding direction serving as the axis.

FIGS. 9A to 9Eare diagrams illustrating the movement ranges of the first rotating member40A and the second rotating member40B. It should be noted thatFIGS. 9A to 9Edo not illustrate the fiber passage pipe30arranged inside the rotating member40and the optical fiber bundle6passing through the fiber passage pipe30.FIG. 9Aillustrates the middle position of the first rotating member40A and the second rotating member40B. The “middle position” is the position in the middle of the movement range of the rotating member40. At the middle position, the two first bundling member passage parts41A and the two second bundling member passage parts41B are aligned. The first rotating member40A and the second rotating member40B each oscillate within the range between 120 degrees clockwise and 120 degrees counter-clockwise (i.e., within the range of ±120 degrees) with the middle position serving as the center. Herein, “oscillation” refers to a to-and-from rotating motion with the feeding direction serving as the axis.

As illustrated inFIGS. 9B and 9C, when viewed from one side in the length direction, the first rotating member40A rotates by 120 degrees clockwise from the middle position, and the second rotating member40B rotates 120 degrees counter-clockwise from the middle position. The first bundling member passage parts41A and the second bundling member passage parts41B pass each other within a range from the state ofFIG. 9Bto the state ofFIG. 9C. Thus, the four bundling members10are fed in the feeding direction while an intersection point between the bundling member10A and the bundling member10D is formed and an intersection point between the bundling member10B and the bundling member10C is formed on the outer circumference of the optical fiber bundle6at the rotating member40's downstream end in the feeding direction.

When the first rotating member40A and the second rotating member40B reach respective ends in their movement ranges, their rotating directions are reversed, and the first rotating member40A and the second rotating member40B rotate to the respective other ends of their movement ranges. For example, after the first rotating member40A rotates clockwise and the second rotating member40B rotates counter-clockwise as illustrated inFIGS. 9B and 9C, the first rotating member40A then rotates counter-clockwise and the second rotating member40B rotates clockwise as illustrated inFIGS. 9D and 9E. The first bundling member passage parts41A and the second bundling member passage parts41B pass each other also within a range from the state ofFIG. 9Dto the state ofFIG. 9E. Thus, an intersection point between the bundling member10A and the bundling member10D is formed and an intersection point between the bundling member10B and the bundling member10C is formed on the outer circumference of the optical fiber bundle6at the rotating member40′s downstream end in the feeding direction.

Focusing on the bundling member10A and the bundling member10D, an intersection point is formed within the range from the state ofFIG. 9Bto the state ofFIG. 9C, and an intersection point is formed within the range from the state ofFIG. 9Dto the state ofFIG. 9E. The two intersection points are located on opposite sides from one another across the optical fiber bundle6. The two intersection points formed on the opposite sides across the optical fiber bundle6are each fusion-bonded in the heating unit50. In this way, the two joining points15AD are formed so as to sandwich the optical fiber bundle6, as illustrated inFIGS. 1A and 5B.

Similarly, focusing on the bundling member10B and the bundling member10B, an intersection point is formed within the range from the state ofFIG. 9Bto the state ofFIG. 9C, and an intersection point is formed within the range from the state ofFIG. 9Dto the state ofFIG. 9E. The two intersection points are located on opposite sides from one another across the optical fiber bundle6. The two intersection points formed on the opposite sides across the optical fiber bundle6are each fusion-bonded in the heating unit50. In this way, the two joining points15BC are formed so as to sandwich the optical fiber bundle6, as illustrated inFIGS. 1A and 5B.

Each bundling member10is wound so as to ultimately cover half the outer circumference of the optical fiber bundle6(i.e., 180 degrees). On the other hand, the rotating member40(the first rotating member40A and the second rotating member40B) that feeds each bundling member10is rotated by an angle (240 degrees) that is greater than the winding angle (180 degrees) at which the bundling member10is ultimately wound. This configuration is employed to suppress/prevent the intersection point between the two bundling members10from disappearing during the period after the bundling members10are fed out from the rotating member40until the bundling members10are joined in the heating unit50, even if the bundling members10unwind and the winding angle of each bundling member10decreases.

It should be noted that, as illustrated inFIG. 8B, the respective downstream ends, in the feeding direction, of the fiber passage pipe30, the first rotating member40A, and the second rotating member40B are located substantially at the same position. The optical fiber bundle6is fed out from the fiber passage pipe30's downstream end in the feeding direction, and the bundling members10are fed out from the respective downstream ends, in the feeding direction, of the first rotating member40A and the second rotating member40B. When the first rotating member40A and the second rotating member40B oscillate with their feeding directions serving as the axis, the first bundling member passage parts41A and the second bundling member passage parts41B move to and from, with their feeding directions serving as the axis, so as to depict an arc on the outer circumference of the optical fiber bundle6. Thus, the bundling members10are fed into the heating unit50on the downstream side in the feeding direction while intersection points between the two bundling members10are formed on the outer circumference of the optical fiber bundle6at the rotating member40′s downstream end in the feeding direction.

The heating unit50is a member (heater) that heats the intersection points between the bundling members10and fusion-bonds the bundling members10at their intersection points. The heating unit50is arranged downstream from the fiber passage pipe30and the rotating member40in the feeding direction. The heating unit50has a unit passage part51(through hole) through which the optical fiber unit2(the optical fiber bundle6and the bundling members10) is passed. When the optical fiber bundle6and the bundling members10, which constitute the optical fiber unit2, pass through the heating unit50, there are intersection points of the four bundling members10formed on the outer circumference of the optical fiber bundle6. These intersection points are fusion-bonded together by being heated by the heating unit50, and thus, the bundling members10are joined together.

With the aforementioned production method, as illustrated inFIG. 5B, the bundling member10A is not only fusion-bonded and joined with the bundling member10D (corresponding to “another bundling member”) at the reverse sections where their winding directions with respect to the optical fiber bundle6are reversed, but also fusion-bonded and joined with the bundling member10B (corresponding to a “different bundling member from said another bundling member”) at the intersection points between the bundling member10B and the bundling member10A. It should be noted that the method for producing the optical fiber unit2is not limited to the aforementioned method, and other methods may be employed. Also, the joining of the bundling members10is not limited to fusion-bonding by applying heat, and bonding with an adhesive may be employed.

If the angle of rotation of the rotating member40(the first rotating member40A and the second rotating member40B) is made smaller in the aforementioned method, the bundling members10can alternatively be joined together as illustrated in the comparative example (FIG. 12B). It should be noted that, to join the bundling members10as in the comparative example illustrated inFIG. 12B, the oscillation period of the rotating member40has to be shortened. As a result, when the optical fiber unit2is produced, an abnormal tension is applied to the bundling members10, which may make the joining points consecutively defective. In contrast, when the bundling members10are joined as in the present embodiment (FIG. 5B) by the aforementioned production method, the oscillation period of the rotating member40can be made long, which is advantageous in that the joining points15are less likely to be faulty.

Second Embodiment

Each optical fiber unit2in the first embodiment includes four bundling members10, but the number of the bundling members10may be four or more. Each optical fiber unit2in a second embodiment includes six bundling members10.

FIG. 10is a developed view of the bundling members10according to the second embodiment. Also in the second embodiment, each bundling member10is wound on the outer circumference of the optical fiber bundle6along the length direction of the optical fiber bundle6while the winding direction of each bundling member10is reversed alternately. Each bundling member10is joined with another bundling member10at reverse sections where its winding direction is reversed. For example, a bundling member10A is wound on the outer circumference of the optical fiber bundle6along the length direction of the optical fiber bundle6while the winding direction is reversed alternately. The bundling member10A is joined with another bundling member10F at the reverse sections where its winding direction is reversed.

The second embodiment includes three pairs of bundling members10whose winding directions are reversed at joining points15(the first embodiment included two pairs of bundling members10). More specifically, in the second embodiment, the three pairs of bundling members10include a pair of the bundling member10A and the bundling member10F, a pair of a bundling member10B and a bundling member10C, and a pair of a bundling member10D and a bundling member10E. The phase of each pair of bundling members10is shifted from that of another pair of bundling members10by 120 degrees. In this way, the position of each joining point15(for example, a joining point15AF) of each pair of bundling members10is shifted from that of a joining point (for example, a joining point15BC or a joining point15DE) of another pair of bundling members10in the length direction.

InFIG. 10, a region surrounded by the pair of bundling members10joined at reverse sections is cross-hatched. In the figure, the cross-hatching indicates a region surrounded by the bundling member10A and the bundling member10F between a joining point15AF at a reverse section where their winding directions are reversed in a predetermined direction and a joining point15AF at the next reverse section where their winding directions are reversed in the same direction. In other words, the region surrounded by the bundling member10A and the bundling member10F corresponding to one pitch is cross-hatched. Stated differently, one mesh cell formed of the pair of bundling members10(the bundling member10A and the bundling member10F) joined at the joining points15AF is cross-hatched.

Also in the second embodiment, the cross-hatched region includes a joining point15BC and a joining point15DE which are at reverse sections of other pairs of bundling members10. In this manner, in the present embodiment, a region surrounded by a pair of bundling members10(the bundling member10A and the bundling member10F in this example) to be joined at the reverse sections—where their winding directions are reversed in a predetermined direction—includes a joining point15at one of the reverse sections of another pair of bundling members10(in the example, the pair of the bundling member10B and the bundling member10C or the pair of the bundling member10D and the bundling member10E). In this way, even if the joining points15AF are consecutively faulty, the joining point15BC and the joining point15DE (joining points in the cross-hatched region) prevent the mesh of the bundling members10that covers the outer circumference of the optical fiber bundle6from breaking. Therefore, also in the second embodiment, even if the joining points15AF are consecutively faulty, it is possible to keep the state where the optical fiber bundle6is bundled by the bundling members10.

Further, in the second embodiment, the cross-hatched region includes a plurality of joining points15(two in this example) at the reverse sections of other pairs of bundling members10. With this configuration, in the second embodiment, at the time of mid-span branching, a worker needs to separate one joining point15(for example, the joining point15AD) with the hands, and also needs to separate the plurality of joining points15(for example, the joining point15BC and the joining point15DE) in the region surrounded by the pair of bundling members10joined at the one joining point15. In the second embodiment, since the joining points15that are to be separated at the time of mid-span branching are not arranged along the length direction, workability of the second embodiment is inferior to that of the first embodiment. However, the joining of the bundling members10is stronger, which is thus advantageous in that it is possible to easily keep the state where the optical fiber bundle6is bundled.

Also in the second embodiment, a range on the outer circumferential surface of the optical fiber bundle6occupied by one bundling member10includes another bundling member10. For example, the range from 0 degrees to 180 degrees on the outer circumferential surface of the optical fiber bundle6occupied by the bundling member10A includes a plurality of other bundling members10(the bundling member10B, the bundling member10C, the bundling member10D, and the bundling member10E in this example). In other words, also in the second embodiment, the range on the outer circumferential surface of the optical fiber bundle6occupied by the one bundling member10overlaps the ranges on the outer circumferential surface of the optical fiber bundle6occupied by other bundling members10. With this configuration, even if, for example, the joining points15AF are consecutively faulty and thereby the bundling member10A cannot perform the function of bundling the optical fiber bundle6, the other bundling members10prevent the mesh of the bundling members10that covers the outer circumference of the optical fiber bundle6from breaking.

Further, the second embodiment includes three pairs of bundling members10whose winding directions are reversed at the joining points15, and each pair of bundling members is wound around the entire circumference of the optical fiber bundle6. With this configuration, even if the joining points15(for example, the bundling members15AF) of one pair of bundling members10(for example, the bundling member10A and the bundling member10F) are consecutively faulty, the other pairs of bundling members10can keep the state where the optical fiber bundle6is bundled.

It should be noted that, also in the second embodiment, each bundling member10may not only be joined with another bundling member10at the reverse sections where their winding directions with respect to the optical fiber bundle6are reversed, but may also be joined with a different bundling member10from said another bundling member at the intersection points between the different bundling member and the bundling member10. For example, the bundling member10A may not only be joined with the bundling member10F at the reverse sections where their winding directions with respect to the optical fiber bundle6are reversed, but may also be joined with the bundling member10B and/or the bundling member10D at the intersection points between the bundling member10B or the bundling member10D and the bundling member10A. This strengthens the joining of the bundling members10, which makes it easy to keep the state where the optical fiber bundle6is bundled.

Third Embodiment

In the foregoing embodiments, each bundling member10is wound on the outer circumference of the optical fiber bundle6and is arranged such that the bundling member depicts an arc covering half the circumference of the bundle (i.e., 180 degrees) along the length direction of the optical fiber unit2. Also in the foregoing embodiments, each bundling member10is joined with the same bundling member10at the reverse sections where their winding directions are reversed, irrespective of the direction in which its winding direction is reversed. It should be noted that the angle at which the bundling member10is wound in the S-Z configuration around the circumference is not limited to 180 degrees. In addition, each bundling member10may be joined with a different bundling member10depending on the direction in which its winding direction is reversed.

FIG. 11is a developed view of bundling members10according to a third embodiment. Also in the third embodiment, each bundling member10is wound on the outer circumference of the optical fiber bundle6along the length direction of the optical fiber bundle6while the winding direction of each bundling member10is reversed alternately. Each bundling member10is joined with another bundling member10at reverse sections where its winding direction is reversed.

Each bundling member10is wound on the outer circumference of the optical fiber bundle6and is arranged such that the bundling member depicts an arc covering ⅓ of the circumference of the bundle (i.e., 120 degrees) along the length direction of the optical fiber unit2. For example, a bundling member10A is wound on the outer circumference of the optical fiber bundle6along the length direction of the optical fiber bundle6while the winding direction is reversed alternately. In this way, the bundling member10A is arranged on the outer circumference of the optical fiber bundle6within a range from 0 degrees to 120 degrees.

Further, each bundling member10is joined with different bundling members10depending on the direction in which its winding direction is reversed. For example, the bundling member10A is joined with a bundling member10D at joining points15AD at reverse sections where the winding direction of the bundling member10A is reversed in a predetermined direction. Also, the bundling member10A is joined with a bundling member10F at joining points15AF at reverse sections where the winding direction of the bundling member10A is reversed in the opposite direction.

InFIG. 11, a region surrounded by a pair of bundling members10joined at reverse sections is cross-hatched. In the figure, the cross-hatching indicates a region surrounded by the bundling member10A and the bundling member10D between a joining point15AD at a reverse section where their winding directions are reversed in a predetermined direction and a joining point15AD at the next reverse section where their winding directions are reversed in the same direction. In other words, the region surrounded by the bundling member10A and the bundling member10D corresponding to one pitch is cross-hatched. Stated differently, one mesh cell formed of the pair of bundling members10(the bundling member10A and the bundling member10D) joined at the joining points15AD is cross-hatched.

Also in the third embodiment, the cross-hatched region includes a joining point15BC at a reverse section of another pair of bundling members10. With this configuration, even if the joining points15AD are consecutively faulty, the joining point15BC (joining point in the cross-hatched region) prevents the mesh of the bundling members10that covers the outer circumference of the optical fiber bundle6from breaking. Therefore, also in the third embodiment, even if the joining points15AD are consecutively faulty, it is possible to keep the state where the optical fiber bundle6is bundled by the bundling members10.

In the third embodiment, the joining points15to be separated at the time of branching are arranged along the length direction, similarly to the first embodiment. In other words, one joining point15(for example, the joining point15AD) and another joining point15(for example, the joining point15BC) which is of a different pair of bundling members10and which is in the region surrounded by the pair of bundling members10joined at the one joining point15are arranged along the length direction. With this configuration, also in the third embodiment, after separating a discretionary joining point15, the worker can sequentially separate the joining points15adjacent to the separated joining point15in the length direction with the separated joining point15as a starting point. Thus, it is easier to locate the joining points15to separate.

Also in the third embodiment, a range on the outer circumferential surface of the optical fiber bundle6occupied by one bundling member10includes another bundling member10. For example, the range from 0 degrees to 120 degrees on the outer circumferential surface of the optical fiber bundle6occupied by the bundling member10A includes another bundling member10B. In other words, also in the third embodiment, the range on the outer circumferential surface of the optical fiber bundle6occupied by one bundling member10overlaps the range on the outer circumferential surface of the optical fiber bundle6occupied by another bundling member10. With this configuration, even if the joining points15AD are consecutively faulty and thereby the bundling member10A cannot perform the function of bundling the optical fiber bundle6, the other bundling member10B prevents the mesh of the bundling members10that covers the outer circumference of the optical fiber bundle6from breaking.

It should be noted that, also in the third embodiment, each bundling member10may not only be joined with another bundling member10at the reverse sections where their winding directions with respect to the optical fiber bundle6are reversed, but may also be joined with a different bundling member10from the other bundling member at the intersection points between the different bundling member and the bundling member10. For example, the bundling member10A may not only be joined with the bundling member D and the bundling member10F at the reverse sections where the winding direction of the bundling member10A with respect to the optical fiber bundle6is reversed, but may also be joined with the bundling member10B at intersection points between the bundling member10B and the bundling member10A. This strengthens the joining of the bundling members10, which makes it easy to keep the state where the optical fiber bundle6is bundled.

Other Embodiments

The foregoing embodiments are for facilitating the understanding of the present invention, and are not to be construed as limiting the present invention. It goes without saying that the present invention may be modified and/or improved without departing from the gist thereof, and that the present invention encompasses any equivalents thereof.

Number of Bundling Members10:

The foregoing embodiments describe examples in which the number of bundling members10wound on the optical fiber bundle6is four or six. However, the number of bundling members10to be provided in a single optical fiber unit2is not limited thereto. For example, the number of bundling members may be eight or more or an odd number.

The aforementioned rotating member40is constituted by the first rotating member40A and the second rotating member40B. It should be noted that the number of rotatable members constituting the rotating member40is not limited to two and may be three or more. Further, although the aforementioned rotating member is constituted by a circular-cylindrical member (pipe), the rotating member may, for example, be constituted by a ring-shaped member.

REFERENCE SIGNS LIST