US 12,754,387 B2Granted

Fiber optic cable

AssigneeNTT, Inc.

InventorsYusuke Yamada, Kazuhide Nakajima

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Abstract

An object of the present invention is to ensure low crosstalk for all multi-core optical fibers in an optical fiber cable having a plurality of identical multi-core optical fibers of non-coupling type in different spiral shapes. An optical fiber cable according to the present disclosure is an optical fiber cable formed by twisting a plurality of units each of which is formed by bundling a plurality of identical multi-core optical fibers of non-coupling type, which includes: that all the units have the same diameter; that the units are arranged in a plurality of layers from a center in a cross section; that the units are arranged in a spiral shape for each of the layers in a longitudinal direction; that all the units included in one of the layers have the same twist pitch of the spiral shape; and that the twist pitch is different for each layer, and is set based on a curvature Rpk of the multi-core optical fiber where crosstalk is the largest.

Claims4

Dependent claims

An optical fiber cable formed by twisting a plurality of units each of which is formed by bundling a plurality of identical multi-core optical fibers, comprising:

that all the units have the same diameter;
that the units are arranged in a plurality of layers from a center in a cross section;
that the units are arranged in a spiral shape for each of the layers in a longitudinal direction;
that all the units included in one of the layers have the same twist pitch of the spiral shape;
and
that the twist pitch is different for each layer, and is set based on a curvature Rpk of the multi-core optical fiber where crosstalk is the largest, wherein
a twist radius r1 of the spiral shape of the unit arranged in an innermost layer being set by a Math. C1;
a curvature ρ1 of the spiral shape of the unit arranged in the innermost layer being set by a Math. C2;
a curvature ρm of the spiral shape of the unit arranged in a specific layer different from the innermost layer being set by a Math. C3;
and
a twist pitch Pm of the spiral shape of the units arranged in the specific layer being set by a Math. C4,
wherein the curvature Rpk does not coincide with the curvature ρ1;
[
Math
.
C1
]

r
⁢
1
=
d
/
{
2
×
sin
⁡
(
π
/
n
)
}
(
C
⁢
1
)
[
Math
.
C2
]

ρ
⁢
1
=
r
⁢
1
/
(
r
⁢
1
2
+
P
⁢
1
/
2
⁢
π
)
2
)
(
C2
)
[
Math
.
C3
]

ρ
m
=
{
r
⁢
1
+
d
⁡
(
m
-
1
)
}
/
[
{
r
⁢
1
+
d
⁡
(
m
-
1
)
}
2
+
(
Pm
/
2
⁢
π
)
2
]
(
C3
)
[
Math
.
C4
]

Pm
=
2
⁢
π
⁢
r
⁢
1
+
d
⁡
(
m
-
1
)
·
r
⁢
1
2
+
(
P
⁢
1
2
⁢
π
)
2
-
[
r
⁢
1
+
d
⁡
(
m
-
1
)
]
2
r
⁢
1
(
C4
)
Where d represents the diameter, n represents the number of units in the innermost layer, P1 represents a twist pitch of the spiral shape of the units arranged in the innermost layer and m represents the number of layers from the center of the specific layer when the innermost layer assumes a first layer.

181 more elements

Dependencies are inferred from the claim text.