DESCRIPTION
OPTICAL FIBER RIBBON CAPABLE OF BRANCHING AND METHOD FOR
MAKING FIBER RIBBON BRANCH
TECHNICAL FIELD
The present invention relates to an optical fiber
ribbon capable of branching and a method for making the
ribbon branch.
BACKGROUND ART
For the purpose of establishing plural separate
optical communications, optical fiber ribbons each of which
has a plurality of optical fibers bundled in a tape-like
shape have been available for these years. A plurality of
such optical fiber ribbons are further bundled and the
whole of them is covered with a sheath, thereby a single
optical fiber cable is structured and then laid down. Such
an optical fiber cable after being laid may be in some
cases subject to a work referred to as "intermediate post-
branching" in which one or more cores are drawn out and
linked with another optical fiber cable. In carrying out
the intermediate post-branching, first it is required that
the sheath of the ribbons is split for the purpose of
drawing out one or more cores and then each optical fiber
ribbon is made to branch. This work usually requires

specialized tools.
At a time of implementation of the intermediate post-
branching, the sheath is split and thus a bend is given to
the optical fiber, thereby transmission loss sometimes
increases. In a case where the subjecc optical fiber
ribbon includes an optical fiber just being used for
communication, namely a "hot line" optical fiber, it is
very important to prevent increase in transmission loss
induced by bending.
Related arts are disclosed in Japanese Patent
Applications Laid-open No. H09-80297, 2005-62427, 2005-
292518, H01-138516, 2005-352510 and 2006-030684, and
Utility Model Application Laid-open No. S59-22404.
DISCLOSURE OF INVENTION
The present invention has an object to provide an
optical fiber ribbon which are readily made to branch by
means of versatile tools with suppressing transmission loss
induced by bending, and a method for making the optical
fiber ribbon branch.
In accordance with a first aspect of the present
invention, an optical fiber ribbon capable of branching by
means of a tool having a width (X) is comprised of: a
plurality of optical fibers running in parallel, each of
the optical fibers having an allowable radius of curvature;
a blanket sheath totally covering the plurality of the

optical fibers; one or more concavities formed at any one
or more intermediates among the optical fibers; and slits
respectively arranged in series at a regular interval along
the concavities, the slits penetrating the blanket sheath
and allowing the tool to be inserted and the blanket sheath
to split by means of movement of the tool along the
concavities, each of the slits having a length prior to
insertion of the tool so determined that flexures of the
optical fibers induced by the tool widening the slits do
not exceed the allowable radius of curvature.
Preferably, each of the optical fibers has an outer
diameter (D) , the blanket sheath has a thickness (t1) from
the respective optical fibers to a surface, each of the
concavities has a thickness (t2), and a length (A), the
allowable redius of curvature (R) , and the intervals (B)
satisfy: Y ≤ A < 500mm, Y < A+B ≤ 500mm, 0.01 ≤ A/(A+B) <1,
0 < t2 < D+2tl, and wherein Y is a
lower limit length of the slits.
Alternatively preferably, each of the optical fibers
has an outer diameter (D), the blanket sheath has a
thickness (tl) from the respective optical fibers to a
surface, each of the concavities has a thickness (t2), and
a length (A), and the intervals (B) satisfy: Y ≤ A < 500mm,
Y < A+B ≤ 500mm, 0.01 ≤ A/(A+B) <1, 0 < t2 < D+2t1, and

, wherein Y is a lower limit length of
the slits.
Alternatively still preferably, the thickness (t1)
satisfies 0 < tl ≤ 0.025mm.
In accordance with a second aspect of the present
invention, a method for making an optical fiber ribbon
branch, the optical fiber ribbon comprising a plurality of
optical fibers running in parallel, each of the optical
fibers having an allowable radius of curvature; a blanket
sheath totally covering the plurality of the optical
fibers; one or more concavities formed at any one or more
intermediates among the optical fibers; and slits
penetrating the blanket sheath, is comprised of: inserting
a tool having a width so determined that flexures of the
optical fibers induced by the tool widening the slits do
not exceed the allowable radius of curvature into one
selected from the slits; and moving the tool along the
concavities to split the blanket sheath.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view of an optical fiber
ribbon according to an embodiment of the present invention,
which shows a cross section thereof in part;
FIG. 2 is a conceptual drawing showing a state where
a slit in the optical fiber ribbon is widened; and

FIG. 3 is a perspective view of an optical fiber
ribbon according to an alternative embodiment of the
present invention, which shows a cross section in part.
BEST MODE FOR CARRYING OUT THE INVENTION
Exemplary embodiments of the present invention will
be described hereinafter with reference to FIGs. 1 through
3.
Referring to FIG. 1, an optical fiber ribbon 1 in
accordance with an embodiment includes a plurality of
optical fibers 3 running in parallel. Each of the optical
fibers 3 may be either a bare fiber or a fiber cord, and
the whole of them is covered with a blanket sheath 5 so as
to form a tape. As the optical fibers 3 form a single
layer, the optical fiber ribbon 1 is relatively thin and
therefore preferably applicable to space-saving uses. Of
course, the optical fibers 3 may be made to form a
plurality of layers. Further, for the purpose of
distinction of the optical fibers 3, these surfaces or any
faces may be colored.
On the blanket sheath 5, at any one or more
intermediates among optical fibers 3, concavities 5A are
formed. Each of the concavities 5A is formed over the
entire length in its longitudinal direction of the blanket
sheath 5. Respectively along the concavities 5A, slits 7
are formed. The slits 7 are arranged in series at regular

intervals B along the concavities and penetrate the blanket
sheath 5 in its thickness direction so as to allow a tool
13 to be inserted therein. Each of the concavities 5A may
have a neck portion substantially parallel to its bottom
portion.
While the slits 7 give structural separation between
partial ribbons 1A, 1B from the outset, portions 9 which
are the concavities 5A but the slits 7 establish junction
between the partial ribbons 1A, 1B.
In the embodiment shown in FIG. 1, an optical fiber
ribbon 1 contains eight optical fibers 3. When numbers #1
through #8 are attached to these optical fibers 3 one by
one from one end thereof, a concavity 5A is formed in an
intermediate between the #4 optical fiber 3 and the #5
optical fiber 3. By using this concavity 5A and the slits
7 formed along the concavity 5A, the blanket sheath 5 can
split so that the optical fiber ribbon 1 can be divided
into a partial ribbon 1A including the #1 through #4
optical fibers 3 and a partial ribbon 1B including the #5
through #8 optical fibers 3.
FIG. 1 exemplarily shows that the #4 and #5 optical
fibers 3 are to some extent apart from each other.
Although such a structure is preferable in view of easiness
of forming the slits 7 and suppression of curvature of the
optical fibers 3, the #4 and #5 optical fibers 3 may be
modified to mutually adjoin. Further, the number of the

optical fibers 3, and the position and the number of the
concavities 5A are also not limited to those described
above.
The work of separating the optical fiber ribbon 1 can
be executed without any tool, nowever, any proper tool 13
may be used for the purpose of preventing the optical fiber
3 from bending. As the tool 13, any versatile member such
as a wire rod having a round, or somehow differently shaped,
cross section. The tool 13 is inserted into any of the
slits 7 and then moved along the concavity 5A, thereby
splitting the blanket sheath 5 along a splitting line 11
and then separating the optical fiber ribbon 1.
When the tool 13 is inserted into one of the slits 7,
the radius of curvature of the related optical fiber 3
decreases (flexure thereof increases). If the radius of
curvature falls below an allowable radius of curvature, the
transmission loss increases to exceed an allowable limit.
Thus the slit 7 is so dimensioned that the radius of
curvature of the optical fiber resulting from widening of
the slit by the tool 13 is kept larger than the allowable
radius of curvature as described hereinafter. More
specifically, as exemplarily shown in FIG. 2, the tool 13
inserted into one of the slit 7 widens the slit 7 so that
flexure is induced on one of the optical fiber 3 adjacent
to the slit 7. at issue. As this flexure can be
approximated by an arc, when a radius of curvature by this

flexure is r, a width of the tool 13 (or a diameter if its
cross section is round) is X, and a length of the slit 7
prior to insertion of the tool 13 is A, a relation among
them is represented by the following equation.

Therefore, to prevent the radius of curvature r from
falling below the allowable radius of curvature R, the
length A of the slit 7 can be determined on the basis of
the following inequality.

Here, Y represents a lower limit of the length of the
slit 7 so as not to fall below the allowable radius of
curvature R. As the allowable radius of curvature R is
typically 30mm for instance, the length A of the slit 7 can
be determined on the basis of the following inequality,
(see FIG. 2)

Then the radius of curvature of the optical fiber 3
is assured to be larger than 30mm that is the allowable
radius of curvature, therefore increase in transmission
loss of the optical fiber led from separation of the
optical fiber ribbon 1 can be sufficiently suppressed.
At a time of intermediate branching of an optical

fiber cable such as an SZ-type optical fiber cable, it is
required to peel off a sheath of the cable over the length
of 500mm. The concavity 5A preferably has at least one
junction portion 9 (a portion not a slit 7 in the concavity
5A) .
Taking the aforementioned matters into consideration,
provided that a lower limit length of the list 7 is Y, the
length A of the slit 7 preferably satisfies the following
inequalities.

Further, when a thickness of the blanket sheath 5
from the optical fiber 3 to a surface thereof is t1 and a
thickness of the concavity 5A is t2, t2 is preferably
within a range of 0 < t2 < D+2t1. As being capable of
splitting with a relatively small force, the concavity 5A
structured in this way effectively prevents application of
an excessive force to the optical fiber 3. More
specifically, as flexure of the optical fiber 3 is
suppressed, increase in transmission loss is suppressed.
Although in the above arguments a wire rod having a
round cross section is exemplified as the tool 13, of

course any tools of various shapes such as a sheet or a
square pillar having a width X can be used.
As being understood from the above explanation, the
number of optical fibers is arbitrary in the present
embodiment of the present invention and a concavity
including slits may be formed at any intermediate between
any pair of the optical fibers. Further the number of
concavities is also arbitrary. Further the shape of the
concavity may be formed in a shape having a roughly V-
shaped cross section instead of the shape shown in FIG. 1.
As an example in such a structure, an embodiment shown in
FIG. 3 is possible. In the embodiment shown in FIG. 3, as
each gap between adjacent optical fibers having a concavity
is made as narrow as possible, the concavity is necessarily
roughly V-shaped. Such an optical fiber ribbon 1 including
a plurality of optical fibers 3 is made to branch into a
plurality of ribbons 1A, 1B, 1C... each including a smaller
number of optical fibers 3.
Further, if the thickness t1 from the optical fiber 3
to the surface of the blanket sheath 5 is in a range of 0 <
tl ≤ 0.025mm, the plurality of ribbons 1A, 1B, 1C... each
including a smaller number of optical fibers 3 are readily
respectively made to branch into ribbons each including a
single optical fiber 3. Still further, instead of the
versatile tool, a tool for shearing disclosed in Japanese
Patent Application Laid-open No. 2006-030684, or a tool for

realizing branching by means of a projection disclosed in
2006-030684, may be used for instance.
To demonstrate effects served by the aforementioned
embodiments, the following measurements have been carried
out. More specifically, an optical fiber ribbon i
containing eight optical fibers 3 shown in FIG. 1 has been
produced, separated into optical fiber ribbons 1A, 1B each
containing four of the optical fibers 3, and further
respectively separated into optical fiber ribbons each
including only one of the optical fibers 3, and then change
of transmission loss is measured at each occasion of
separation. A concavity 5A is formed at an intermediate
between a #4 optical fiber and a #5 optical fiber, and
slits 7 are formed to be arranged in series at regular
intervals B along the concavity 5A.
Here, a single-mode optical fiber (SMF) regulated in
JIS-C6835 or ITUT-G652 and an SR10 optical fiber in
conformity to ITUT-G652B are applied to the optical fiber 3.
An optical fiber of an SR10 equivalence is an optical fiber
that has transmission of 0.50dB or less in regard to light
of 1.550pm in wavelength when the fiber is bent to make 10
turns with a bending diameter O of 20mm.
The length A of the slit 7 is 72mm and the interval B
is 8mm. More specifically, A+B is 80mm and A/(A+B) is 0.9.
Given that a wire rod of 0.2mm in diameter is used as a
tool, the aforementioned condition in which

Y < A < 500mm,
Y < A+B ≤ 500mm, and
0.01 ≤ A/(A+B) < 1, is satisfied.
Table 1 summarizes measurement results in which
transmission loss change in a case where the optical fiber
ribbon 1 is separated into two optical fiber ribbons 1A, 1B
is measured. Table 1 shows two cases, one is related to a
case where a wire rod of 0.2mm in diameter is used and
another is related to a case where a tool by shearing is
used.
[Table 1]
Loss change at a time of separation
8 cores -> 4 cores

As being understood from Table 1, in any optical
fibers, and in any tools, changes in transmission loss are
1dB or less. Thus degradation of transmission properties

is suppressed. Further in any case, the work of
intermediate post-branching can be easily carried out.
Table 2 summarizes measurement results in which
transmission loss change in a case where the separated
optical fiber ribbons 1A or 1B is further separated into
optical fiber ribbons each including a single optical fiber
is measured. Table 2 shows three cases, one is related to
a case where a wire rod of 0.2mm in diameter is used,
another is related to a case where a tool with a file is
used, and the other is related to a case where a tool for
realizing branching by means of a projection is used.
[Table 2]

As being understood from Table 2, in a case where the

optical fiber of SMF is used, change in transmission loss
is 1dB or larger even if any tools are used, but separation
is possible. In a case where the optical fiber of the SR
equivalence is used, as change in transmission loss is ldB
or less even if any tools are used, degradation of
transmission properties induced by bending is sufficiently
suppressed and further the work of intermediate post-
branching can be very easily carried out.
The optical fiber ribbon 1 provides the following
effects. More specifically, as it has a concavity
including slits having a proper length A, bending of the
optical fibers is suppressed when a tool for branching is
inserted into any of the slits, thereby suppressing
increase in transmission loss. By moving the tool along
the concavity, the concavity splits and thus the optical
fiber ribbon 1 easily becomes capable of branching.
The blanket sheath 5 can be produced only from one
layer of a resin. This leads to a possibility for
production of a very thin optical fiber ribbon 1 can be
produced. A very thin optical fiber ribbon 1 is not only
space-saving but also does facilitate the work of branching.
Because the optical fiber ribbon 1 has a structure or
shape similar to that of a conventional multi-core optical
fiber ribbon, it can be used compatibly with the
conventional multi-core optical fiber ribbon, apart from
differences in properties such as easiness of branching.

Although the invention has been described above by
reference to certain exemplary embodiments of the invention,
the invention is not limited to the exemplary embodiments
described above. Modifications and variations of the
embodiments described above will occur to those skilled in
the art, in light of the above teachings.
INDUSTRIAL APPLICABILITY
An optical fiber ribbon which is readily made to
branch by means of versatile tools with suppressing
transmission loss by bending and a method for making the
optical fiber ribbon branch are provided.

CLAIMS
1. An optical fiber ribbon capable of branching by means
of a tool having a width (X) , the optical fiber ribbon
comprising:
a plurality of optical fibers running in parallel,
each of the optical fibers having an allowable radius of
curvature;
a blanket sheath totally covering the plurality of
the optical fibers;
one or more concavities formed at any one or more
intermediates among the optical fibers; and
slits respectively arranged in series at a regular
interval along the concavities, the slits penetrating the
blanket sheath and allowing the tool to be inserted and the
blanket sheath to split by means of movement of the tool
along the concavities, each of the slits having a length
prior to insertion of the tool so determined that flexures
of the optical fibers induced by the tool widening the
slits do not exceed the allowable radius of curvature.
2. The optical fiber ribbon of claim 1, wherein each of
the optical fibers has an outer diameter (D), the blanket
sheath has a thickness (t1) from the respective optical
fibers to a surface, each of the concavities has a
thickness (t2), and a length (A), the allowable redius of
curvature (R), and the intervals (B) satisfy:
Y < A < 500mm,


wherein Y is a lower limit length of the slits.
3. The optical fiber ribbon of claim 1, wherein each of
the optical fibers has an outer diameter (D), the blanket
sheath has a thickness (t1) from the respective optical
fibers to a surface, each of the concavities has a
thickness (t2), and a length (A), and the intervals (B)
satisfy:

wherein Y is a lower limit length of the slits.
4. The optical fiber ribbon of claim 2, wherein the
thickness (t1) satisfies 0 < t1 ≤ 0.025mm.
5. A method for making an optical fiber ribbon branch,
the optical fiber ribbon comprising a plurality of optical
fibers running in parallel, each of the optical fibers
having an allowable radius of curvature; a blanket sheath
totally covering the plurality of the optical fibers; one

or more concavities formed at any one or more intermediates
among the optical fibers; and slits penetrating the blanket
sheath, the method comprising:
inserting a tool having a width so determined that
flexures of the optical fibers induced by the tool widening
the slits do not exceed the allowable radius of curvature
into one selected from the slits; and
moving the tool along the concavities to split the
blanket sheath.

An optical fiber tape core wire can be branched using some tool. The optical fiber tape core wire comprises a
plurality of optical fibers running in parallel, a collective coating which covers the plurality of optical fibers entirely, a recess formed
in at least any one gap between the optical fibers and on the collective coating, and a plurality of slits arranged in series along each
recess at a predetermined interval and permitting cleavage of the collective coating by inserting a tool through the collective coating
and moving the tool along the recess. Length of the slit is set such that the bend of the optical fiber caused by spreading the slit with
the tool does not exceed the allowable radius of curvature of the optical fiber.