[Technical Field]
5 [0001]
The present invention relates to an optical cable and an
optical-cable manufacturing method.
[Background Art]
[0002]
10 There is a known technique for forming an optical fiber
cable using an optical fiber unit which is an optical fiber
assembly formed by a plurality of optical fibers bundled
together. In a method commonly used for this, a roughlywinding thread (a bundling member) is wrapped around the bundle
15 of optical fibers to keep the bundle of optical fibers from
coming apart, and the color of the bundling member is used for
identification of the optical fiber unit. For example, PTL 1
discloses a technique for forming an optical fiber unit by
bundling a plurality of optical fiber ribbons together to make
20 a bundle.
[Citation List]
[Patent Literature]
[0003]
[PTL 1] Japanese Patent Application Publication No. 2007-
25 233252
[Summary of Invention]
[Technical Problem]
[0004]
In a case where an optical fiber unit is formed by
30 bundling a plurality of optical fiber ribbons together, it is
a common practice that, as described in PTL 1, the plurality
of the optical fiber ribbons are bundled together in a stacked
manner (in a manner that the optical fiber ribbons are overlaid
on top of one another). However, when an optical cable is
35 formed using an optical fiber unit formed by a plurality of
3
optical fiber ribbons that are bundled together in a stacked
manner as described in PTL 1, there is a concern that when the
optical cable receives a load (such as, e.g., a bend or a
temperature change), the load may be concentrated at particular
5 optical fibers, which consequently increases transmission loss.
[0005]
The present invention has an object to reduce load
concentration at particular optical fibers.
[Solution to Problem]
10 [0006]
A main aspect of the invention to achieve the above
object is an optical cable comprising a plurality of optical
fiber units, wherein the optical fiber unit has a plurality of
intermittently-coupled optical fiber ribbons, in a cross
15 section perpendicular to a longitudinal direction, at least
one of the optical fiber units is such that a length of a
vector GU is shorter than a largest length of vectors MG of
the plurality of the optical fiber ribbons, where the vector
MG is a vector starting from a midpoint M and ending at a
20 center of gravity G, M is the midpoint between optical fibers
at both ends of each optical fiber ribbon, G is the center of
gravity of the optical fiber ribbon, and the vector GU is a
resultant vector of the vectors MG of the respective optical
fiber ribbons.
25 [0007]
Other features of the present invention will become
apparent in the following description and the drawings.
[Advantageous Effects of Invention]
[0008]
30 The present invention can reduce load concentration at
particular optical fibers.
[Brief Description of Drawings]
[0009]
[Fig. 1] Fig. 1A is a diagram illustrating an optical cable 1.
35 Fig. 1B is a diagram illustrating an optical fiber unit 2.
4
[Fig. 2] Fig. 2 is a diagram illustrating an intermittentlycoupled optical fiber ribbon 7.
[Fig. 3] Fig. 3 is a diagram illustrating a unit manufacturing
apparatus 20 that manufactures the optical fiber unit 2.
5 [Fig. 4] Fig. 4 is a diagram illustrating a bundle attaching
section 50.
[Fig. 5] Fig. 5A is a diagram illustrating the cross-sectional
shape of the optical fiber unit 2 of the optical cable 1 of
the present embodiment. Fig. 5B is a graph showing the
10 coordinates of optical fibers 8 shown in Fig. 5A.
[Fig. 6] Figs. 6A and 6B are diagrams illustrating vectors MG
and a vector GU.
[Fig. 7] Fig. 7A is a diagram illustrating the cross-sectional
shape of the first optical fiber ribbon 7 in Fig. 5A. Fig. 7B
15 is a diagram illustrating a comparative case where the optical
fiber ribbon 7 is bent in one direction relative to the ribbon
width direction.
[Fig. 8] Fig. 8 is a diagram illustrating a first method for
manufacturing the optical fiber unit 2 in an irregularly
20 stacked state.
[Fig. 9] Fig. 9 is a sectional view of a bundle joining section
60 in the first manufacturing method.

[CLAIMS]
[Claim 1]
An optical cable comprising a plurality of optical fiber
units, wherein
5 the optical fiber unit has a plurality of intermittentlycoupled optical fiber ribbons,
in a cross section perpendicular to a longitudinal
direction, at least one of the optical fiber units is such
that
10 a length of a vector GU is shorter than a largest length
of vectors MG of the plurality of the optical fiber ribbons,
where the vector MG is a vector starting from a midpoint
M and ending at a center of gravity G, M is the midpoint
between optical fibers at both ends of each optical fiber
15 ribbon, G is the center of gravity of the optical fiber ribbon,
and the vector GU is a resultant vector of the vectors MG of
the respective optical fiber ribbons.
[Claim 2]
The optical cable according to claim 1, wherein
20 in all the optical fiber units of the optical cable, at
least in any given cross section in a longitudinal direction,
the length of the vector GU is shorter than the largest length
of the vectors MG of the plurality of the optical fiber ribbons
forming the optical fiber unit.
25 [Claim 3]
The optical cable according to claim 2, wherein
the plurality of optical fiber units are twisted together,
and
in all the optical fiber units of the optical cable, in
30 any given cross section taken within a range of a twisting
pitch, the length of the vector GU is shorter than the largest
length of the vectors MG of the plurality of the optical fiber
ribbons forming the optical fiber unit.
[Claim 4]
35 The optical cable according to any one of claims 1 to 3,
49
wherein
the optical fiber unit has a bundling material bundling
the plurality of the optical fiber ribbons.
[Claim 5]
5 The optical cable according to any one of claims 1 to 4,
wherein
in at least one of the optical fiber ribbons forming the
optical fiber unit,
L/L0 is 0.225 or smaller,
10 where L is the length of the vector MG and L0 is a
distance between the optical fibers at both ends of the optical
fiber ribbon in a flat state.
[Claim 6]
The optical cable according to claim 5, wherein
15 L/L0 is 0.149 or smaller.
[Claim 7]
The optical cable according to claim 5, wherein
L/L0 is 0.225 or smaller in all the optical fiber ribbons
forming the optical fiber unit.
20 [Claim 8]
The optical cable according to any one of claims 1 to 7,
wherein
a standard deviation of L/L0 is 0.011 or greater,
where L is the length of the vector MG and L0 is a
25 distance between the optical fibers at both ends of the optical
fiber ribbon in a flat state.
[Claim 9]
The optical cable according to any one of claims 1 to 7,
wherein
30 in at least one of the optical fiber ribbons forming the
optical fiber unit, L1/L0 is 0.205 or greater and 1.490 or
smaller, where L1 is a distance between the optical fibers at
both ends of the optical fiber ribbon and L0 is a distance
between the optical fibers at both ends of the optical fiber
35 ribbon in a flat state.
50
[Claim 10]
The optical cable according to claim 9, wherein
L1/L0 is 0.490 or greater and 1.267 or smaller.
[Claim 11]
5 The optical cable according to claim 9, wherein
L1/L0 is 0.205 or greater and 1.490 or smaller in all
the optical fiber ribbons forming the optical fiber unit.
[Claim 12]
The optical cable according to any one of claims 1 to
10 11, wherein
a standard deviation of L1/L0 of the plurality of the
optical fiber ribbons is 0.018 or greater where L1 is a
distance between the optical fibers at both ends of each
optical fiber ribbon and L0 is a distance between the optical
15 fibers at both ends of the optical fiber ribbon in a flat
state.
[Claim 13]
The optical cable according to any one of claims 1 to
12, wherein
20 in the cross section, at least one of the optical fiber
ribbons of the optical fiber unit has a part that is bent with
one side of a ribbon surface being convex and a part that is
bent with an opposite side of the ribbon surface being convex.
[Claim 14]
25 An optical-cable manufacturing method comprising:
manufacturing an optical fiber unit having a plurality
of intermittently-coupled optical fiber ribbons and
housing a plurality of the optical fiber units inside a
sheath, wherein
30 the optical fiber units are manufactured with a stacked
state of the plurality of the optical fiber units being made
irregular such that in at least one of the optical fiber units,
in a cross section perpendicular to a longitudinal direction,
a length of a vector GU is shorter than a largest length of
35 vectors MG of the plurality of the optical fiber ribbons, where
51
the vector MG is a vector starting from a midpoint M and ending
at a center of gravity G, M is the midpoint between optical
fibers at both ends of each optical fiber ribbon, G is the
center of gravity of the optical fiber ribbon, and the vector
5 GU is a resultant vector of the vectors MG of the respective
optical fiber ribbons.