DESCRIPTION
T
itle of Invention: OPTICAL FIBER UNIT, OPTICAL FIBER
BRANCHING METHOD, AND OPTICAL FIBER CABLE
5
Technical Field
[0001]
The present invention relates to an optical fiber unit,
an optical fiber branching method, and an optical fiber cable.
10
Background Art
[0002]
Techniques are known for forming an optical fiber cable
including optical fiber units which are optical fiber
15 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
20 the optical fiber units to be differentiated from one another
by the colors of the bundling members.
[0003]
In relation to such bundling members, Patent Literature
1 discloses a technique in which a plurality of bundling
25 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
30 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
sections where their winding directions are reversed.
3
C
itation List
Patent Literature
[0004]
5 Patent Literature 1: JP 2011-169939A
Patent Literature 2: JP 2012-88454A
S
ummary of Invention
Technical Problem
10 [0005]
Conventional methods, however, may result in poor
workability at the time of extracting a desired optical fiber
from an optical fiber unit. For example, in Patent Literature
1, a plurality of bundling members are wound helically on the
15 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
20 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
25 fibers.
[0006]
Moreover, in cases where a bundling member is wound
helically on the circumference of a bundle of optical fibers,
or in cases where two bundling members are wound in an S-Z
30 configuration around the circumference of the bundle of
optical fibers as in Patent Literature 2, the optical fibers
may meander when tension is applied to the bundling member(s),
resulting in a possibility of increased transmission loss.
4
[0007]
An objective of the invention is to improve workability
at the time of extracting optical fibers in an optical fiber
unit in which a bundle of optical fibers is bundled by bundling
5 members, and to suppress/prevent an increase in transmission
loss even when tension is applied to the bundling members.
S
olution to Problem
[0008]
10 A primary aspect of the invention for achieving the
aforementioned objective is an optical fiber unit including:
a plurality of optical fibers; and at least three bundling
members that bundle the plurality of optical fibers into a
bundle. A first bundling member, among the plurality of
15 bundling members, is arranged along a length direction of the
bundle of the optical fibers so as to be wound on an outer
circumference of the bundle of the optical fibers. The first
bundling member is joined with a second bundling member at
a contact point where the first bundling member contacts the
20 second bundling member, and is joined with a third bundling
member at a contact point where the first bundling member
contacts the third bundling member, the third bundling member
being different from the second bundling member. The first
bundling member’s winding direction with respect to the
25 bundle of the optical fibers is reversed at the contact point
with the second bundling member and at the contact point with
the third bundling member.
[0009]
Other features of the invention are made clear by the
30 following description and the drawings.
A
dvantageous Effects of Invention
[0010]
5
With the present invention, it is possible to improve
workability at the time of extracting optical fibers in an
optical fiber unit in which a bundle of optical fibers is
bundled by bundling members, and to suppress/prevent an
5 increase in transmission loss even when tension is applied
to the bundling members.
B
rief Description of Drawings
[0011]
10 [Fig. 1] Fig. 1 is a cross-sectional view of an optical
fiber cable 1 according to a first reference example.
[Fig. 2] Fig. 2 is a schematic diagram of an optical fiber
unit 10 according to the first reference example.
[Fig. 3] Fig. 3 is a schematic diagram of an
15 intermittently connected fiber ribbon 11.
[Fig. 4] Fig. 4 is a diagram illustrating a
cross-sectional structure of a bundling member 12.
[Fig. 5] Fig. 5 is a cross-sectional view illustrating
how the bundling members 12 are wound in the first reference
20 example.
[Fig. 6] Fig. 6 is a diagram illustrating an optical fiber
unit according to Comparative Example 1.
[Fig. 7] Fig. 7A is a table showing results comparing the
first reference example and Comparative Example 1 regarding
25 workability in a cable-end operation, and Fig. 7B is a table
showing results comparing the first reference example and
Comparative Example 1 regarding workability in mid-span
branching.
[Fig. 8] Fig. 8 is a cross-sectional view of an optical
30 fiber cable according to a modified example of the first
reference example.
[Fig. 9] Fig. 9 is a schematic diagram of an optical fiber
unit 10 according to a second reference example.
6
[Fig. 10] Fig. 10 is a cross-sectional view illustrating
how the bundling members 12 are wound in the second reference
example.
[Fig. 11] Fig. 11 is a schematic diagram of an optical
5 fiber unit 10 according to a first embodiment.
[Fig. 12] Fig. 12 is a cross-sectional view illustrating
how the bundling members 12 are wound in the first embodiment.
[Fig. 13] Figs. 13A to 13C are explanatory diagrams
illustrating a comparative example wherein a single bundling
10 member 12 is wound helically around the circumference of a
bundle of intermittently connected fiber ribbons 11.
[Fig. 14] Figs. 14A to 14C are explanatory diagrams
illustrating a comparative example wherein two bundling
members 12 are wound in an S-Z configuration on the
15 circumference of a bundle of intermittently connected fiber
ribbons 11, as in the first reference example.
[Fig. 15] Fig. 15 is an explanatory diagram illustrating
a case where a tensile force is applied to the bundling members
12 in the first embodiment.
20 [Fig. 16] Fig. 16 is a table showing evaluation results
of transmission loss.
D
escription of Embodiments
[0012]
25 At least the following matters are made clear from the
following description and the drawings.
[0013]
Disclosed is an optical fiber unit including: a plurality
of optical fibers; and at least three bundling members that
30 bundle the plurality of optical fibers into a bundle. A first
bundling member, among the plurality of bundling members, is
arranged along a length direction of the bundle of the optical
fibers so as to be wound on an outer circumference of the bundle
7
of the optical fibers. The first bundling member is joined
with a second bundling member at a contact point where the
first bundling member contacts the second bundling member,
and is joined with a third bundling member at a contact point
5 where the first bundling member contacts the third bundling
member, the third bundling member being different from the
second bundling member. The first bundling member’s winding
direction with respect to the bundle of the optical fibers
is reversed at the contact point with the second bundling
10 member and at the contact point with the third bundling member.
[0014]
With this optical fiber unit, it is possible to improve
workability at the time of extracting optical fibers, and to
suppress/prevent an increase in transmission loss even when
15 tension is applied to the bundling members.
[0015]
In the aforementioned optical fiber unit, it is
preferable that the plurality of optical fibers are bundled
by four bundling members. With this optical fiber unit, it
20 is possible to suppress/prevent an increase in transmission
loss even when tension is applied to the bundling members.
[0016]
In the aforementioned optical fiber unit, it is
preferable that the bundling members are arranged evenly
25 along the length direction of the bundle of the optical fibers
such that each bundling member depicts an arc covering
one-fourth of the circumference of the bundle. With this
optical fiber unit, it is possible to suppress/prevent an
increase in transmission loss even when tension is applied
30 to the bundling members.
[0017]
In the aforementioned optical fiber unit, it is
preferable that, as viewed from one of the contact points,
8
another one of the contact points is present on the opposite
side of the bundle. With this optical fiber unit, force
applied to the optical fibers is canceled out, and the optical
fibers can be suppressed/prevented from meandering.
5 [0018]
In the aforementioned optical fiber unit, it is
preferable that, when a cross section of the optical fiber
unit is viewed from the length direction of the bundle of the
optical fibers, a polygon is formed by lines that each connect
10 the two contact points of each of the bundling members. With
this optical fiber unit, deformation in which the optical
fibers bend to the inside of the polygon is less likely to
occur, and thus, the optical fibers are less likely to meander.
As a result, it is possible to suppress/prevent an increase
15 in transmission loss.
[0019]
In the aforementioned optical fiber unit, it is
preferable that the range over which each bundling member is
wound with respect to the bundle of the optical fibers is less
20 than or equal to half the outer circumference of the bundle
of the optical fibers. With this optical fiber unit,
deformation of the optical fibers can be further suppressed.
[0020]
In the aforementioned optical fiber unit, it is
25 preferable that: an optical fiber ribbon is formed by a
plurality of the optical fibers that are arranged side by side;
and connection parts that each connect two adjacent ones of
these optical fibers are arranged intermittently in a length
direction and a width direction of the optical fiber ribbon.
30 [0021]
With this optical fiber unit, the optical fibers are
easier to handle and easier to manage because a plurality of
optical fibers are gathered into a ribbon.
9
[0022]
Also disclosed is an optical fiber branching method
involving: peeling off the first bundling member from the
aforementioned optical fiber unit, to thereby enable a
5 predetermined optical fiber to be extracted from the bundle
of the optical fibers.
[0023]
Also disclosed is an optical fiber cable including a
plurality of the aforementioned optical fiber units, the
10 optical fiber units being housed inside the optical fiber
cable.
[0024]
Further, at least the following matters are also made
clear from the following description and the drawings.
15 [0025]
Disclosed is an optical fiber unit including: a plurality
of optical fibers; and a plurality of bundling members that
bundle the plurality of optical fibers into a bundle. A first
bundling member, among the plurality of bundling members, is
20 arranged along a length direction of the bundle of the optical
fibers so as to be wound on an outer circumference of the bundle
of the optical fibers. The first bundling member is joined
with a second bundling member at a contact point where the
first bundling member contacts the second bundling member.
25 The first bundling member’s winding direction with respect
to the bundle of the optical fibers is reversed at the contact
point.
[0026]
With this optical fiber unit, it is possible to improve
30 workability at the time of extracting optical fibers.
[0027]
In the aforementioned optical fiber unit, it is
preferable that the range over which each bundling member is
1 0
wound with respect to the bundle of the optical fibers is less
than one round around the outer circumference of the bundle
of the optical fibers.
[0028]
5 With this optical fiber unit, there is no need to e.g.
retrieve the bundling members helically, and the bundling
member can be peeled off easily, simply by being pulled in
a predetermined direction. Thus, mid-span branching etc. of
the optical fiber cable is facilitated.
10 [0029]
In the aforementioned optical fiber unit, it is
preferable that the first bundling member’s winding direction
with respect to the outer circumference of the bundle of the
optical fibers is in the reverse direction from the second
15 bundling member’s winding direction with respect to the outer
circumference of the bundle of the optical fibers.
[0030]
With this optical fiber unit, the bundling members can
be peeled off easily from the bundle of optical fibers by
20 pulling the two bundling members in mutually opposite
directions.
[0031]
In the aforementioned optical fiber unit, it is
preferable that the second bundling member is arranged
25 rectilinearly along the length direction of the bundle of the
optical fibers.
[0032]
With this optical fiber unit, the bundling member can be
peeled off easily from the bundle of optical fibers by pulling
30 one of the two bundling members.
[0033]
In the aforementioned optical fiber unit, it is
preferable that, in the length direction of the bundle of the
1 1
optical fibers, the distance between two adjacent joined
points between the first bundling member and the second
bundling member is from 30 mm to 200 mm inclusive.
[0034]
5 With this optical fiber unit, it is possible to improve
workability at the time of extracting optical fibers during
mid-span branching etc.
[0035]
{First Reference Example}
10 Structure of Optical Fiber Unit:
The first reference example describes: an optical fiber
unit constituted by a plurality of optical fibers; and an
optical fiber cable including these optical fiber units. Fig.
1 is a cross-sectional view of an optical fiber cable 1
15 according to the first reference example.
[0036]
This optical fiber cable 1 includes: optical fiber units
10 (10A to 10C); a sheath 30; and tension members 40. Each
optical fiber unit 10 is structured so that, by tying a
20 plurality of optical fibers 111 into a bundle with bundling
members 12, the optical fibers 111 are prevented from falling
apart. In Fig. 1, the optical fiber cable 1 is constituted
by three optical fiber units 10, i.e., optical fiber units
10A, 10B, 10C, but the number of optical fiber units 10
25 included in a single optical fiber cable 1 may be varied as
appropriate depending on e.g. the use of the cable. The
circumference of the optical fiber units 10A to 10C is covered
by a wrapping 15 formed of e.g. a nonwoven fabric, and the
outer circumferential part thereof is covered by a sheath 30
30 which is the outer covering of the optical fiber cable 1.
Tension members 40 are provided in the sheath 30.
Optical Fiber Unit 10:
Fig. 2 is a schematic diagram of the optical fiber unit
1 2
10. Fig. 3 is a schematic diagram of an intermittently
connected fiber ribbon 11.
[0037]
The optical fiber unit 10 of the first reference example
5 is made by: closely gathering intermittently connected fiber
ribbons 11, each constituted by a plurality of optical fibers
111, into a bundle; and tying the bundle together by winding
bundling members 12 on the circumference of the bundle.
[0038]
10 The intermittently connected fiber ribbon 11 is what is
called an optical fiber ribbon wherein the optical fibers 111
are formed into a ribbon (tape) form by: arranging a plurality
of optical fibers 111 side by side; and gathering the optical
fibers by connecting two adjacent optical fibers 111 with
15 connection parts 115. In Fig. 3, the intermittently
connected fiber ribbon 11 is formed by four optical fibers
111, but the number of optical fibers 111 for forming the
intermittently connected fiber ribbon 11 is not limited
thereto.
20 [0039]
Each optical fiber 111 is formed by covering the outer
circumference of a bare fiber, which is a transmission path
for transmitting light, with two cover layers (soft and hard).
The bare fiber is made, for example, of a glass material having
25 a diameter of 125 μm. Each cover layer is made, for example,
of an ultraviolet-curable resin or a thermosetting resin. A
coloring layer is formed on the cover layer; the color of the
coloring layer allows the plurality of optical fibers 111 to
be differentiated from one another according to color. In
30 the first reference example, the diameter of the optical fiber
111 including the coloring layer is approx. 250 μm. Note that
the hard layer itself, of the two cover layers, may be colored,
without forming the coloring layer.
1 3
[0040]
The connection part 115 is a member that connects two
optical fibers 111 adjacent to one another in the width
direction. As illustrated in Fig. 3, in the intermittently
5 connected fiber ribbon 11, a plurality of connection parts
115 are arranged intermittently in the length direction and
the width direction of the optical fibers 111. A
predetermined separation distance is provided in the width
direction between two adjacent optical fibers 111. The
10 intermittently connected fiber ribbon 11 is foldable in the
width direction at the sections of the connection parts 115,
and can thus be formed into a bundle as illustrated in Fig.
2.
[0041]
15 It should be noted that the first reference example
encompasses optical fiber units 10 wherein a plurality of
optical fibers 111 are separately gathered into a bundle by
the bundling members 12, instead of forming the optical fibers
111 into a ribbon (tape) form.
20 [0042]
The bundling member 12 is a member for bundling the
intermittently connected fiber ribbons 11 (the plurality of
optical fibers 111), and a plurality of bundling members 12
are provided in a single optical fiber unit 10. As
25 illustrated in Fig. 2, the optical fiber unit 10 of the first
reference example is provided with two bundling members 12,
i.e., bundling members 12A and 12B.
[0043]
Fig. 4 is a diagram illustrating a cross-sectional
30 structure of the bundling member 12. The bundling member 12
includes: a plurality of core parts 121 extending along the
length direction of the optical fiber unit 10; and a cover
part 122 that covers the outer circumference of each of the
1 4
core parts 121 and that has a lower melting point than the
melting point of the core parts 121. The bundling members
12A and 12B can be thermally fusion-bonded at contact points
therebetween by the adhesiveness that arises by heating the
5 cover part 122 at a temperature equal to or higher than the
melting point. Preferably, the difference between the
melting point of the core part 121 and the melting point of
the cover part 122 is 20°C or greater. The melting point of
the core part 121 is preferably approx. 160°C, and the melting
10 point of the cover part 122 is preferably approx. from 90°C
to 130°C. The requirements for the cover part 122 are that:
even when the cover part is heated and molten, the cover part
122 either does not bond with the optical fibers 111 or has
a weak adhesive force even if it bonds with the optical fibers;
15 and the cover part does not cause degradation of the cover
layer(s) of the optical fibers 111.
[0044]
As for the core parts 121 and the cover part 122, it is
possible to use, for example, a high melting point resin such
20 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
25 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 hot-melt adhesive which
30 employs a thermoplastic resin or rubber as a base and which
is capable of reversibly repeating softening and hardening
by heating and cooling.
[0045]
1 5
It should be noted that the bundling members 12A and 12B
do not have to be a composite material of a high melting point
material (core parts 121) and a low melting point material
(cover part 122) as illustrated in Fig. 4, and instead may
5 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
bundling members 12A and 12B may be constituted by different
materials.
10 [0046]
The joining of the bundling member 12A and the bundling
member 12B does not have to be by thermal fusion-bonding, but
may be achieved by using an adhesive. Examples of adhesives
that may be used for joining/bonding the bundling members
15 include reactive adhesives such as epoxy-based adhesives and
modified olefin-based adhesives employing
ultraviolet-curable resins and/or solvents.
[0047]
The two bundling members 12A and 12B are provided with
20 unique colors to allow the optical fiber units 10 to be
differentiated from one another. For example, in Fig. 1,
three optical fiber units--i.e., optical fiber units 10A to
10C--are housed inside the optical fiber cable 1. In this
case, by applying predetermined colors to the bundling
25 members 12 to be wound on the respective optical fiber units
10A to 10C, the optical fiber units 10A to 10C can be
differentiated easily from one another.
[0048]
Fig. 5 is a cross-sectional view illustrating how the
30 bundling members 12 are wound in the first reference example.
In the first reference example, the bundling member 12A is
wound on the outer circumference of the bundle of
intermittently connected fiber ribbons 11 (plurality of
1 6
optical fibers 111) and is arranged along the length direction
of the bundle of optical fibers 111 such that the bundling
member depicts an arc covering half the circumference of the
bundle (cf. Fig. 2). On the other hand, the bundling member
5 12B is arranged so as to depict an arc covering half the
circumference of the bundle in the opposite direction from
the bundling member 12A. The bundling member 12A and the
bundling member 12B are joined at each contact point where
the bundling member 12A and the bundling member 12B contact
10 one another. After the bundling members are joined at the
contact point, the bundling member 12A’s winding direction,
as well as the bundling member 12B’s winding direction, with
respect to the bundle of optical fibers 111 is reversed.
[0049]
15 In the case of Fig. 5, the bundling member 12A is wound
clockwise on the upper side of the outer circumference of the
bundle of intermittently connected fiber ribbons 11, whereas
the bundling member 12B is wound counterclockwise on the lower
side of the outer circumference of the bundle of
20 intermittently connected fiber ribbons 11. Then, after the
bundling members are joined at contact point J11, their
winding directions are reversed; the bundling member 12A is
wound counterclockwise on the upper side of the outer
circumference of the bundle of intermittently connected fiber
25 ribbons 11, whereas the bundling member 12B is wound clockwise
on the lower side of the outer circumference of the bundle
of intermittently connected fiber ribbons 11. Then, the
bundling members are again joined at contact point J12 located
on the opposite side from the contact point J11 with respect
30 to the bundle of intermittently connected fiber ribbons 11.
By repeating this operation, the state as illustrated in Fig.
2 is achieved.
[0050]
1 7
The strength of the joined section between the bundling
members 12A and 12B is preferably of a degree where the joined
section does not get inadvertently disengaged, but can be
disjoined easily with the hands whenever desired. In this
5 way, at the time of mid-span branching in which a specific
optical fiber 111 is extracted from the bundle of optical
fibers 111 included in an optical fiber cable, the
joined/bonded section can be disjoined with the hands and the
extraction site can be widened, without cutting the bundling
10 members 12A and 12B. Moreover, in cases where the joining
strength is less than or equal to the breaking strength of
each bundling member, preferably less than or equal to the
yield point strength, the bundling members 12 can be peeled
off without elongating and breaking.
15 [0051]
It should be noted that the two bundling members 12A and
12B can be re-joined by applying heat with a heater or by
applying an adhesive after the extraction of an optical fiber
111 in mid-span branching.
20 Sheath 30:
The sheath 30 covers the outer circumferential part of
the optical fiber units 10, which are wrapped by a wrapping
15, and protects the optical fiber units 10 located on the
inside (Fig. 1). The sheath 30 is made e.g. of a resin such
25 as polyethylene resin.
Tension Member 40:
The tension member 40 is a tensile member for preventing
tension applied to the optical fiber cable 1 from being
directly transmitted to the optical fibers 111 (Fig. 1). Each
30 tension member 40 is made e.g. of a steel wire.
[0052]
Workability in Mid-Span Branching Etc.:
By employing a comparative example, verification tests
1 8
were performed regarding the workability in mid-span
branching wherein a specific optical fiber 111 is extracted
by peeling off the sheath 30 at a midpoint of the optical fiber
cable 1 in the length direction, and the workability in a
5 cable-end operation wherein a specific optical fiber 111 is
extracted from an end of the optical fiber cable 1 in the length
direction.
[0053]
Fig. 6 is a diagram illustrating an optical fiber unit
10 according to Comparative Example 1. In the optical fiber unit
of Comparative Example 1, the way the bundling members 12 are
wound is different from that in the optical fiber unit 10 of
the first reference example (Fig. 2). The other features are
substantially the same as those in the optical fiber unit 10.
15 As illustrated in Fig. 6, Comparative Example 1 includes two
bundling members, i.e., bundling members 12C and 12D. The
bundling members 12C and 12D are wound helically around the
bundle of intermittently connected fiber ribbons 11
(plurality of optical fibers 111) in opposite directions from
20 one another. The bundling members 12C and 12D are joined
together by thermal fusion-bonding at sections (contact
points) where the bundling members intersect with one
another.
[0054]
25 With respect to an optical fiber cable according to
Comparative Example 1 including the aforementioned optical
fiber units and the optical fiber cable 1 according to the
first reference example, tests were conducted regarding
workability in mid-span branching and in cable-end operation
30 by changing the winding pitch of the bundling members 12.
Note that “winding pitch” refers to the distance between two
adjacent joined points between the bundling members 12 in the
length direction of the optical fiber unit.
1 9
[0055]
Figs. 7A and 7B show verification results for each
operation. Fig. 7A is a table showing evaluation results
comparing the first reference example and Comparative Example
5 1 regarding workability in a cable-end operation. Fig. 7B
is a table showing evaluation results comparing the first
reference example and Comparative Example 1 regarding
workability in mid-span branching. In both cases, GOOD
indicates that the operation can be conducted easily, POOR
10 indicates that the operation is difficult to conduct, and FAIR
indicates that operation is possible but is poorer in
workability than GOOD.
[0056]
In the cable-end operation shown in Fig. 7A, the
15 workability was FAIR for both the first reference example and
Comparative Example 1 in cases where the winding pitch of the
bundling members 12 was 250 mm or longer. This is because,
by widening the winding pitch, the visibility of the bundling
members 12 is impaired and the optical fiber units become
20 difficult to differentiate from one another, thus resulting
in reduced workability. In other cases (i.e., in cases where
the winding pitch was 200 mm or less), the workability was
GOOD for both the first reference example and Comparative
Example 1, indicating that both examples had good workability.
25 In the cable-end operation, even when the sheath 30 at the
cable’s end section is peeled off and the bundling members
12 are pulled toward the opposite side from the cable end,
the bundling members 12 are less prone to disengage from the
bundle of intermittently connected fiber ribbons 11
30 (plurality of optical fibers 111). Thus, there is not much
difference in workability between the first reference example
and Comparative Example 1, even though the methods for winding
the bundling members 12 are different.
2 0
[0057]
Next, in mid-span branching shown in Fig. 7B, as in the
cable-end operation, the workability was FAIR for both the
first reference example and Comparative Example 1 in cases
5 where the winding pitch of the bundling members 12 was 250
mm or longer. This is because widening the winding pitch
impairs the visibility of the bundling members 12. On the
other hand, there was a significant difference between the
first reference example and Comparative Example 1 in cases
10 where the winding pitch was 60 mm or less.
[0058]
In Comparative Example, the workability was POOR in cases
where the winding pitch was 60 mm or less. In cases where
the distance of the winding pitch of the bundling members 12
15 is 60 mm or less, the work space during mid-span branching
is too small; thus, it is difficult to extract a specific
optical fiber 111 from between the joined sections of the
bundling members 12 in a state where the bundling members are
still wound around the bundle. In such cases, it is necessary
20 to peel off the bundling members 12 at the work section and
expose the bundle of intermittently connected fiber ribbons
11 (plurality of optical fibers 111). In Comparative Example
1, the bundling members 12C and 12D are each wound helically
(Fig. 6); thus, in order to expose the optical fibers 111,
25 there is a need to first peel apart the joined sections of
the bundling members 12C and 12D, and then retrieve each
bundling member helically. This requires time and effort to
extract an optical fiber 111 at a midpoint section, in the
length direction, of the optical fiber cable 1. Also, in the
30 retrieving operation, there is a possibility that the optical
fibers 111 may break as a result of e.g. the worker’s finger
getting caught in the optical fibers.
[0059]
2 1
In contrast, in the optical fiber cable 1 of the first
reference example, the workability was GOOD even in cases
where the winding pitch was 60 mm or less. This is because
the way the bundling members 12 are wound in the first
5 reference example is easier to peel than the way the bundling
members 12 are wound in Comparative Example 1, and it is easy
to expose the optical fibers 111. As illustrated in Figs.
2 and 5, the bundling members 12A and 12B of the optical fiber
cable 1 are wound so as to depict an arc covering half the
10 bundle’s circumference. Therefore, by pulling the bundling
members 12A and 12B in mutually opposite directions, the
bundle of intermittently connected fiber ribbons 11
(plurality of optical fibers 111) can be exposed easily while
peeling the joined section. For example, in Fig. 5, the
15 bundling members can be peeled off easily by pulling the
bundling member 12A upward and pulling the bundling member
12B downward. Stated differently, the range over which each
bundling member 12 is wound with respect to the bundle of
intermittently connected fiber ribbons 11 is less than one
20 round around the outer circumference of the bundle of
intermittently connected fiber ribbons 11. Thus, there is
no need to retrieve the bundling members helically, and the
bundling members can be removed easily, simply by pulling one
bundling member (e.g. the bundling member 12A) in a direction
25 that allows this bundling member to be peeled from the other
bundling member (e.g. the bundling member 12B) to which the
aforementioned bundling member is joined. Thus, the work
efficiency in mid-span branching is excellent, even in cases
where the winding pitch is short.
30 [0060]
It should be noted that, even in the optical fiber cable
1 of the first reference example, the workability rating was
FAIR or POOR in a range where the winding pitch was 20 mm or
2 2
less. This is because, depending on the thickness of the
worker’s fingers, it may be difficult to pinch the bundling
members 12 in cases where the distance is around 20 mm.
[0061]
5 From the aforementioned results, it is understood that
mid-span branching etc. can be performed efficiently in a
range where the winding pitch of the bundling members 12 is
from 30 mm to 200 mm.
[0062]
10 As described above, with the optical fiber unit 10
according to the first reference example, it is possible to
improve workability at the time of extracting optical fibers
111.
[0063]
15 Modified Example:
In an optical fiber cable according to a modified example,
the method according to which the optical fiber units 10 are
housed is different. The configuration of each optical fiber
unit 10 and each bundling member 12 is substantially the same
20 as in the first reference example.
[0064]
Fig. 8 is a cross-sectional view of an optical fiber cable
according to a modified example of the first reference example.
The optical fiber cable of the modified example is what is
25 referred to as a slot-type optical fiber cable. A slot-type
optical fiber cable is an optical fiber cable having a
structure in which slots, or grooves, for housing optical
fiber ribbons or separate optical fibers are provided inside
the optical fiber cable.
30 [0065]
The optical fiber cable of the modified example includes:
optical fiber units 10; a slotted core 20; a sheath 30; and
a tension member 40. The functions of the various members
2 3
other than the slotted core 20 are as described in Fig. 1.
[0066]
The slotted core 20 is a member serving as a base part
of the optical fiber cable of the modified example, and has
5 a plurality of slots 21 formed in the outer circumference at
predetermined intervals. In the optical fiber cable
illustrated in Fig. 8, five slots 21 are provided at regular
intervals in the outer circumferential part of the slotted
core 20. Each slot 21 is a groove that is opened outward
10 (toward the outer circumference side) in the radial direction
of the slotted core 20. Ribs 22 are formed on respective sides
of each slot 21. An optical fiber unit 10 gathered into a
bundle is housed in each slot 21. In Fig. 8, the slot 21 is
formed in a substantially U-shape, which allows the bundled
15 optical fiber unit 10 to be housed easily. The number and
the shape of the slots 21 provided in the slotted core 20 may
be changed as appropriate depending on, for example, the
thickness of the optical fiber cable or the number of optical
fibers 111 to be housed.
20 [0067]
In the modified example, the slots 21 are formed so as
to depict a unidirectional helix with respect to the slotted
core 20’s axial direction (the optical fiber cable’s length
direction). Alternatively, the slots 21 may be formed so as
25 to depict what is called an S-Z helical pattern in which the
slots 21 are formed so as to alternately and repeatedly depict
S-twists and Z-twists periodically. In this case, the
optical fiber cable may also be referred to as an S-Z-slotted
optical fiber cable.
30 [0068]
A slot wrapping 25 is provided between the slotted core
20 and the sheath 30. The slot wrapping 25 is a sheet-form
member that covers the outer circumferential part of the
2 4
slotted core 20 so as to envelop the same. By providing the
slot wrapping 25, the sheath 30 can be prevented from sinking
into the opening of each slot 21 from the outside.
[0069]
5 Even in an optical fiber cable structured as above, the
workability in mid-span branching can be improved by winding,
with respect to each optical fiber unit 10 housed inside the
cable, the bundling members 12 in the same way as in the first
reference example.
10 [0070]
{Second Reference Example}
The second reference example describes an example in
which the way the bundling members are wound in an optical
fiber unit is changed. The fundamental features of the
15 optical fiber cable are substantially the same as in the first
reference example.
[0071]
Fig. 9 is a schematic diagram of an optical fiber unit
10 according to the second reference example. Fig. 10 is a
20 cross-sectional view illustrating how the bundling members
12 are wound in the second reference example. The optical
fiber unit 10 of the second reference example includes two
bundling members, i.e., bundling members 12E and 12F.
[0072]
25 The bundling member 12E is wound on the outer
circumference of the bundle of intermittently connected fiber
ribbons 11 (plurality of optical fibers 111) and is arranged
along the length direction of the bundle of the optical fibers
111 such that the bundling member depicts an arc covering one
30 round of the circumference of the bundle (cf. Fig. 9). The
bundling member 12F (illustrated with hatch lines in Fig. 9)
is arranged rectilinearly along the length direction of the
bundle of optical fibers 111. The bundling members 12E and
2 5
12F are joined at each contact point where the bundling member
12E and the bundling member 12F contact one another. After
the bundling members are joined at the contact point, the
bundling member 12E’s winding direction with respect to the
5 bundle of optical fibers 111 is reversed.
[0073]
In the case of Fig. 10, the bundling member 12E is wound
clockwise on the outer circumference of the bundle of
intermittently connected fiber ribbons 11, and comes into
10 contact at contact point J21 with the bundling member 12F
arranged on the lower side of the bundle. Then, after the
bundling members are joined at contact point J21, the bundling
member 12E’s winding direction is reversed; the bundling
member 12E is wound counterclockwise on the outer
15 circumference of the bundle of intermittently connected fiber
ribbons 11, and again comes into contact with, and is joined
to, the bundling member 12F at contact point J22. By
repeating this operation, the state as illustrated in Fig.
9 is achieved.
20 [0074]
The optical fiber unit 10 according to the second
reference example also has excellent workability in mid-span
branching and in cable-end operation. For example, in cases
where the bundling members 12 need to be peeled off from the
25 bundle of intermittently connected fiber ribbons 11 at the
time of mid-span branching, it is only necessary to pull the
bundling member 12E upward, or pull the bundling member 12F
downward, in Fig. 10. In this way, the joined sections
between the bundling members 12E and 12F are peeled apart,
30 and the bundling members 12 can be peeled off easily from the
bundle of intermittently connected fiber ribbons 11. More
specifically, also in the second reference example, because
the range over which each bundling member is wound with respect
2 6
to the bundle of intermittently connected fiber ribbons 11
is less than one round, there is no need to e.g. retrieve the
bundling members helically, and the bundling member can be
peeled off easily simply by being pulled in a predetermined
5 direction. Thus, the work efficiency in mid-span branching
etc. is excellent.
[0075]
{First Embodiment}
The first embodiment describes an example in which the
10 number of bundling members in an optical fiber unit is
increased. The fundamental features of the optical fiber
cable are substantially the same as in the first reference
example.
[0076]
15 Fig. 11 is a schematic diagram of an optical fiber unit
10 according to the first embodiment. Fig. 12 is a
cross-sectional view illustrating how the bundling members
12 are wound in the first embodiment. The optical fiber unit
10 according to the first embodiment includes four bundling
20 members, i.e., bundling members 12G, 12H, 12I, and 12J.
[0077]
The bundling member 12G is wound on the outer
circumference of the bundle of intermittently connected fiber
ribbons 11 (plurality of optical fibers 111) and is arranged
25 along the length direction of the bundle of optical fibers
111 such that the bundling member depicts an arc covering
one-fourth of the circumference of the bundle (cf. Fig. 9).
Similarly, each of the bundling members 12H to 12J is wound
on the outer circumference of the bundle of intermittently
30 connected fiber ribbons 11 (plurality of optical fibers 111)
and is arranged along the length direction of the bundle of
optical fibers 111 such that the bundling member depicts an
arc covering one-fourth of the circumference of the bundle.
2 7
The bundling member 12G and the bundling member 12H are joined
at each contact point where the bundling member 12G and the
bundling member 12H contact one another, and at each joined
point, the bundling member 12G’s winding direction, as well
5 as the bundling member 12H’s winding direction, with respect
to the bundle of optical fibers 111 is reversed. Also, the
bundling member 12G and the bundling member 12J are joined
at each contact point where the bundling member 12G and the
bundling member 12J contact one another, and at each joined
10 point, the bundling member 12G’s winding direction, as well
as the bundling member 12J’s winding direction, with respect
to the bundle of optical fibers 111 is reversed. When
focusing on the bundling member 12G, the bundling member 12G
(corresponding to the first bundling member) is joined with
15 the bundling member 12H (corresponding to the second bundling
member) at a contact point J31 where the bundling member 12G
contacts the bundling member 12H, and is joined with the
bundling member 12J (corresponding to the third bundling
member) at a contact point J32 where the bundling member 12G
20 contacts the bundling member 12J; and the bundling member
12G’s winding direction with respect to the bundle of
intermittently connected fiber ribbons 11 (plurality of
optical fibers 111) is reversed at the contact point J31 and
at the contact point J32. Similarly, for the other bundling
25 members (e.g. the bundling member 12H), the bundling member
is joined with an adjacent bundling member 12 (e.g. bundling
member 12G) at a contact point where it contacts the adjacent
bundling member, and is joined with another adjacent bundling
member (e.g. bundling member 12I) at a contact point where
30 it contacts this other bundling member; and the bundling
member’s winding direction with respect to the bundle of
intermittently connected fiber ribbons 11 (plurality of
optical fibers 111) is reversed at the two contact points (e.g.
2 8
contact points J31 and J33).
[0078]
In the case of Fig. 12, the bundling member 12G is wound
clockwise on the outer circumference of the bundle of
5 intermittently connected fiber ribbons 11. On the other hand,
the bundling member 12H is wound counterclockwise on the outer
circumference of the bundle of intermittently connected fiber
ribbons 11. After the bundling members are joined at contact
point J31, the bundling member 12G’s winding direction, as
10 well as the bundling member 12H’s winding direction, is
reversed. The bundling member 12G is wound counterclockwise
on the outer circumference of the bundle of intermittently
connected fiber ribbons 11, and is joined with the bundling
member 12J at contact point J32 which is the contact point
15 with the bundling member 12J; then, its winding direction is
again reversed. On the other hand, the bundling member 12H’s
winding direction is reversed at contact point J31, and is
wound clockwise on the outer circumference of the bundle of
intermittently connected fiber ribbons 11, and is joined with
20 the bundling member I at contact point J33 which is the contact
point with the bundling member I; then, its winding direction
is again reversed. Similarly, the bundling member 12I and
the bundling member 12J are joined at contact point J34, and
then, their winding directions are reversed. By repeating
25 this operation, the state as illustrated in Fig. 11 is
achieved.
[0079]
The optical fiber unit 10 according to the first
embodiment also has excellent workability in mid-span
30 branching and in cable-end operation. For example, in cases
where the bundling members 12 need to be peeled off from the
bundle of intermittently connected fiber ribbons 11 at the
time of mid-span branching, each bundling member can be peeled
2 9
off easily by pulling one of the bundling members 12G to 12J
outward in the radial direction of the optical fiber unit 10
in Fig. 12. Also in the present embodiment, because the range
over which each bundling member is wound with respect to the
5 bundle of intermittently connected fiber ribbons 11 is less
than one round, there is no need to e.g. retrieve the bundling
members helically, and the bundling member can be peeled off
easily simply by being pulled in a predetermined direction.
Further, in the present embodiment, any desired bundling
10 member among the four bundling members 12G to 12J can be peeled
off selectively. Thus, work can be conducted in a state where
the other bundling members in locations that do not require
peeling are left as-is; also, the bundle of intermittently
connected fiber ribbons 11 are less likely to fall apart, and
15 work can be conducted even more efficiently.
[0080]
Advantages of Employing Three or More Bundling Members
12:
Employing three or more bundling members 12, as in the
20 first embodiment, not only improves the workability at the
time of extracting optical fibers 111, but also offers the
advantage that an increase in transmission loss can be
suppressed/prevented even when tension is applied to the
bundling members 12. Hereinbelow, comparative examples
25 using one or two bundling members 12 will be described first,
and then, the advantages of employing three or more bundling
members 12 will be described.
[0081]
Figs. 13A to 13C are explanatory diagrams illustrating
30 a comparative example wherein a single bundling member 12 is
wound helically around the circumference of a bundle of
intermittently connected fiber ribbons 11. Fig. 13A is an
explanatory diagram illustrating a state in which a tensile
3 0
force in the length direction is applied to the single,
helically wound bundling member 12. Fig. 13B is an
explanatory diagram illustrating the force applied from the
bundling member 12 to the optical fibers 111. Fig. 13C is
5 an explanatory diagram illustrating how the optical fibers
meander.
[0082]
In cases where a tensile force in the length direction
is applied to the bundling member 12 (cf. Fig. 13A), the
10 bundling member 12 attempts to deform so that it passes along
the shortest distance, and the bundling member 12 attempts
to deform so as to come close to a straight line. Stated
differently, when viewing a cross section from the length
direction as illustrated in Fig. 13B, the bundling member
15 12--which depicts a circular path--attempts to deform toward
the center of the circular path (or toward the barycentric
position of the bundling member 12 when viewing a cross section
from the length direction). Thus, when viewing a cross
section from the length direction as illustrated in Fig. 13B,
20 the optical fibers 111 receive, from the bundling member 12,
a force toward the center of the bundling member 12’s circular
path. As a result, the optical fibers 111 meander along the
length direction as illustrated in Fig. 13C, thus giving rise
to an increase in transmission loss of optical signals.
25 Particularly in cases where the optical fiber cable shrinks
in the length direction due to temperature changes as
described further below, there is a particularly noticeable
increase in transmission loss.
[0083]
30 Figs. 14A to 14C are explanatory diagrams illustrating
a comparative example wherein two bundling members 12 are
wound in an S-Z configuration on the circumference of a bundle
of intermittently connected fiber ribbons 11, as in the first
3 1
reference example. Fig. 14A is an explanatory diagram
illustrating a state in which a tensile force in the length
direction is applied to the two bundling members 12. Fig.
14B is an explanatory diagram illustrating the force applied
5 from the bundling members 12 to the optical fibers 111. Fig.
14C is an explanatory diagram illustrating how the optical
fibers meander.
[0084]
Also in cases where a tensile force in the length
10 direction is applied to the two bundling members 12 (Fig. 14A),
each bundling member 12 attempts to deform so that it passes
along the shortest distance, and each bundling member 12
attempts to deform so as to come close to a straight line.
The winding direction of each bundling member 12 is reversed
15 at the contact point J with the other bundling member 12; thus,
when viewing a cross section from the length direction as
illustrated in Fig. 14B, each bundling member 12 attempts to
deform toward the inner side of a region surrounded by the
semicircular path and the line connecting the two contact
20 points J, and thus attempts to deform toward the line
connecting the two contact points J. Thus, when viewing a
cross section from the length direction as illustrated in Fig.
14B, the optical fibers 111 receive, from each bundling member
12 depicting a semicircular path, a force toward the line
25 connecting the two contact points J.
[0085]
In cases where there are two bundling members 12 as in
the first reference example, when viewing a cross section from
the length direction as illustrated in Fig. 14B, the line
30 connecting the two contact points J of one bundling member
12 matches the line connecting the two contact points J of
the other bundling member 12. Thus, in cases where a tensile
force is applied to the two bundling members 12, the two
3 2
bundling members 12 attempt to deform toward the same line
when viewing a cross section from the length direction as
illustrated in Fig. 14B. Further, when viewing a cross
section from the length direction as illustrated in Fig. 14B,
5 the bundling members 12 attempt to deform such that one contact
point J moves toward the other contact point J. As a result,
the optical fibers 111 meander along the length direction as
illustrated in Fig. 14C, thus giving rise to an increase in
transmission loss of optical signals. Particularly in cases
10 where the optical fiber cable shrinks in the length direction
due to temperature changes as described further below, there
is a particularly noticeable increase in transmission loss.
[0086]
Further, in cases where there are two bundling members
15 12 as in the first reference example, as viewed from a certain
contact point J of the bundling members 12, no contact point
J is present on the opposite side of the bundle of
intermittently connected fiber ribbons 11 as illustrated in
Fig. 14A (that is, the contact point on the opposite side is
20 located at a different position in the length direction).
Thus, when one contact point J moves toward the center of the
bundle of intermittently connected fiber ribbons 11, the
optical fibers 111 will meander along the length direction.
[0087]
25 Fig. 15 is an explanatory diagram illustrating a case
where a tensile force is applied to the bundling members 12
in the first embodiment.
[0088]
Also in cases where a tensile force in the length
30 direction is applied to the bundling members 12 of the first
embodiment, each bundling member 12 attempts to deform so that
it passes along the shortest distance, and each bundling
member 12 attempts to deform so as to come close to a straight
3 3
line. The winding direction of each bundling member 12 is
reversed at each contact point J; thus, when viewing a cross
section from the length direction as illustrated in Fig. 15,
each bundling member 12 attempts to deform toward the inner
5 side of a region surrounded by the arc-shaped path and the
line connecting the two contact points J, and thus attempts
to deform toward the line connecting the two contact points
J. Thus, when viewing a cross section from the length
direction as illustrated in Fig. 15, the optical fibers 111
10 receive, from each bundling member 12 depicting an arc-shaped
path, a force toward each line (the dotted line in the figure)
connecting two contact points J.
[0089]
In cases where there are three or more bundling members
15 12 as in the first embodiment, a certain bundling member 12
(e.g. bundling member 12G) can be arranged such that its
winding direction with respect to the bundle of optical fibers
111 is reversed at a contact point with an adjacent bundling
member (e.g. bundling member 12H) and at a contact point with
20 another adjacent bundling member (e.g. bundling member 12J).
By arranging the bundling members 12 in this way, when viewing
a cross section from the length direction as illustrated in
Fig. 15, the line connecting the two contact points J of a
certain bundling member 12 does not match the line connecting
25 the two contact points J of another bundling member 12, but
a polygon (a square in this example) is formed by the lines
that each connect the two contact points J of each of the
bundling members 12. Thus, when each bundling member 12
attempts to deform toward the inner side of a region surrounded
30 by the arc-shaped path and the line connecting the two contact
points J, each bundling member 12 is in a state where it is
less likely to deform to the inside of this polygon. Further,
when viewing a cross section from the length direction as
3 4
illustrated in Fig. 15, even when a certain bundling member
12 attempts to deform such that one contact point J, among
the two contact points J of that bundling member 12, moves
toward the other contact point J, the bundling member 12 is
5 in a state where it is less likely to deform into the space
inside this polygon.
[0090]
It should be noted that, in cases where a polygon (a square
in this example) is formed by the lines that each connect the
10 two contact points J of each of the bundling members 12, it
is preferable that the range over which each bundling member
12 is wound with respect to the bundle of optical fibers 111
is less than or equal to half the outer circumference of the
bundle of optical fibers 111. Stated differently, it is
15 preferable that the maximum angle of the path of each bundling
member 12 as viewed from the length direction is less than
or equal to 180 degrees. In this way, the center of the bundle
of optical fibers 111 is located on the inner side of the region
surrounded by the polygon, and the cross-sectional area of
20 the region surrounded by the polygon is increased; thus, the
deformation of the optical fibers 111 can be further
suppressed.
[0091]
Accordingly, in cases where there are three or more
25 bundling members 12 as in the first embodiment, even if tension
is applied to the bundling members 12, the optical fibers 111
are less likely to deform so as to bend to the inside of the
polygon illustrated in Fig. 15 (i.e., the polygon formed by
the lines that each connect the two contact points J of each
30 of the bundling members 12 when viewing a cross section from
the length direction as illustrated in Fig. 15). Thus, in
the first embodiment, the optical fibers 111 are less likely
to meander. As a result, it is possible to suppress/prevent
3 5
an increase in transmission loss. Further, even in cases
where the optical fiber cable shrinks in the length direction
due to temperature changes, an increase in transmission loss
can be suppressed/prevented, as described below.
5 [0092]
Further, in cases where there are four bundling members
12 as in the first embodiment, as viewed from a certain contact
point J, another contact point J is present on the opposite
side of the bundle of intermittently connected fiber ribbons
10 11, as illustrated in Fig. 11. Thus, when one contact point
J attempts to move toward the center of the bundle of
intermittently connected fiber ribbons 11, another contact
point J located on the opposite side of the bundle of
intermittently connected fiber ribbons 11 from the
15 aforementioned contact point J also attempts to move toward
the center of the bundle of intermittently connected fiber
ribbons 11. As a result, force applied to the optical fibers
111 is canceled out, and the optical fibers 111 can be
suppressed/prevented from meandering. It should be noted
20 that, in cases where there are four bundling members 12, if
the bundling members 12 are arranged evenly along the length
direction of the bundle of optical fibers 111 such that each
bundling member 12 depicts an arc covering one-fourth of the
circumference of the bundle as illustrated in Fig. 11, there
25 will be another contact point J present on the opposite side
of the bundle of optical fibers 111 as viewed from a certain
contact point J of one of the bundling members 12, and thus,
the optical fibers 111 can be suppressed/prevented from
meandering.
30 [0093]
Fig. 15 illustrates an example where there are four
bundling members 12, but it will suffice to provide at least
three bundling members 12. In cases where there are at least
3 6
three bundling members 12, a polygon (e.g. a triangle) can
be formed by the lines that each connect the two contact points
J of each of the bundling members 12 when viewing a cross
section from the length direction. As a result, the optical
5 fibers 111 are less likely to meander, and thus, it is possible
to suppress/prevent an increase in transmission loss.
[0094]
Next, transmission loss was studied by producing optical
fiber cables having the structure illustrated in Fig. 1.
10 [0095]
As examples of optical fiber cables having helically
wound bundling members 12, a single-wind optical fiber cable
with one bundling member 12 wound helically in one direction
(cf. Fig. 13A), and a cross-wound optical fiber cable with
15 two bundling members 12 wound helically in opposite
directions from one another (cf. Fig. 6) were prepared. It
should be noted that, in these optical fiber cables, the angle
of each bundling member 12’s path was 360 degrees when viewing
a cross section from the length direction.
20 [0096]
As optical fiber cables having two bundling members 12
wound in an S-Z configuration, three types of optical fiber
cables--in each of which the angle of the bundling member 12’s
path was different when viewing a cross section from the length
25 direction--were prepared. In each of the cables, the maximum
angle of the bundling member 12’s path when viewing a cross
section from the length direction was 270 degrees, 225 degrees,
or 180 degrees. (In each case, the angle of the other bundling
member 12’s path was 90 degrees, 135 degrees, or 180 degrees.)
30 [0097]
As optical fiber cables having three bundling members 12
wound in an S-Z configuration, three types of optical fiber
cables--in each of which the angle of the bundling member 12’s
3 7
path was different when viewing a cross section from the length
direction--were prepared. In each of the cables, the maximum
angle of the bundling member 12’s path when viewing a cross
section from the length direction was 240 degrees, 180 degrees,
5 or 120 degrees. Similarly, as optical fiber cables having
four bundling members 12 wound in an S-Z configuration, three
types of optical fiber cables--in each of which the angle of
the bundling member 12’s path was different when viewing a
cross section from the length direction--were prepared. In
10 each of the cables, the maximum angle of the bundling member
12’s path when viewing a cross section from the length
direction was 180 degrees, 120 degrees, or 90 degrees.
[0098]
The density of the optical fibers 111 in each optical
15 fiber cable was 10 fibers/mm2 in each optical fiber cable.
The winding pitch of the bundling members 12 was 100 mm in
each optical fiber cable.
[0099]
Transmission loss was measured according to Temperature
20 Cycling per IEC 60794-1-2 at an initial value of +20°C and
low and high temperatures of -30°C and +70°C. The measurement
results are shown in Fig. 16. It should be noted that the
transmission loss at low temperature or high temperature as
shown in the table is the transmission loss of a selected one
25 of the optical fibers in a cycle, among the three cycles
conducted, with the greatest transmission loss.
[0100]
As regards the evaluation results shown in the table,
samples in which the amount of increase in loss with respect
30 to the initial state was 0.07 dB or greater were rated as POOR,
and samples in which the amount of increase in loss was less
than 0.07 dB were rated as GOOD. From the evaluation results
shown in the table, it can be verified that excellent results
3 8
are obtained by optical fiber cables in which three or more
bundling members 12 are wound in an S-Z configuration.
[0101]
{Other Embodiments}
5 The foregoing embodiments are for facilitating the
understanding of the present invention, and are not to be
construed as limiting the present invention. The present
invention may be modified and/or improved without departing
from the gist thereof, and it goes without saying that the
10 present invention encompasses any equivalents thereof.
[0102]
Intermittently Connected Fiber Ribbon:
The foregoing embodiment describes an example in which
the intermittently connected fiber ribbon 11 is formed by
15 connecting four optical fibers 111. However, the number of
optical fibers constituting the intermittently connected
fiber ribbon 11 is not limited thereto; the number of optical
fibers may be increased or decreased. Also, the connecting
positions and the number of the aforementioned connection
20 parts 115 for connecting two adjacent optical fibers 111 may
be changed depending on the use of the intermittently
connected fiber ribbon 11.
[0103]
Number of Bundling Members:
25 The foregoing embodiment describes an example in which
there are four bundling members wound on the bundle of optical
fibers. However, the number of bundling members to be
provided in a single optical fiber unit is not limited thereto.
For example, there may be three, or five or more, bundling
30 members. However, considering the amount of water-absorbing
substances supplied by the bundling members and the
workability during mid-span branching of the optical fiber
cable as described above, it is preferable to provide a
3 9
plurality of bundling members per single optical fiber unit
and allow each bundling member to be peeled off easily.
R
eference Signs List
5 [0104]
1: Optical fiber cable;
10: Optical fiber unit;
10A, 10B, 10C: Optical fiber units;
11: Intermittently connected fiber ribbon;
10 111: Optical fiber;
115: Connection part;
12: Bundling member;
12A to 12J: Bundling members;
15: Wrapping;
15 20: Slotted core;
21: Slot;
22: Rib;
25: Slot wrapping;
30: Sheath;
20 40: Tension member.
4 0

CLAIMS
Claim. 1 An optical fiber unit comprising:
a plurality of optical fibers; and
5 at least three bundling members that bundle the plurality
of optical fibers into a bundle, wherein:
a first bundling member, among the plurality of bundling
members, is arranged along a length direction of the bundle
of the optical fibers so as to be wound on an outer
10 circumference of the bundle of the optical fibers;
the first bundling member is joined with a second bundling
member at a contact point where the first bundling member
contacts the second bundling member, and is joined with a third
bundling member at a contact point where the first bundling
15 member contacts the third bundling member, the third bundling
member being different from the second bundling member; and
the first bundling member’s winding direction with
respect to the bundle of the optical fibers is reversed at
the contact point with the second bundling member and at the
20 contact point with the third bundling member.
[
Claim 2] The optical fiber unit according to claim 1,
wherein the plurality of optical fibers are bundled by four
bundling members.
25
[Claim 3] The optical fiber unit according to claim 2,
wherein the bundling members are arranged evenly along the
length direction of the bundle of the optical fibers such that
each bundling member depicts an arc covering one-fourth of
30 the circumference of the bundle.
[
Claim 4] The optical fiber unit according to claim 2 or
3, wherein, as viewed from one of the contact points, another
4 1
one of the contact points is present on the opposite side of
the bundle.
[
Claim 5] The optical fiber unit according to any one of
5 claims 1 to 4, wherein, when a cross section of the optical
fiber unit is viewed from the length direction of the bundle
of the optical fibers, a polygon is formed by lines that each
connect the two contact points of each of the bundling members.
[
10 Claim 6] The optical fiber unit according to claim 5,
wherein the range over which each bundling member is wound
with respect to the bundle of the optical fibers is less than
or equal to half the outer circumference of the bundle of the
optical fibers.
15
[Claim 7] The optical fiber unit according to any one of
claims 1 to 6, wherein:
an optical fiber ribbon is formed by a plurality of the
optical fibers that are arranged side by side; and
20 connection parts that each connect two adjacent ones of
these optical fibers are arranged intermittently in a length
direction and a width direction of the optical fiber ribbon.
[
Claim 8] An optical fiber branching method comprising:
25 peeling off the first bundling member from the optical
fiber unit according to any one of claims 1 to 7, to thereby
enable a predetermined optical fiber to be extracted from the
bundle of the optical fibers.
[
30 Claim 9] An optical fiber cable comprising a plurality
of the optical fiber units according to any one of claims 1
to 7, the optical fiber units being housed inside the optical
fiber cable.