Optical waveguides – Optical transmission cable – Ribbon cable
Reexamination Certificate
2000-04-17
2002-08-13
Patel, Tulsidas (Department: 2839)
Optical waveguides
Optical transmission cable
Ribbon cable
C385S113000
Reexamination Certificate
active
06434306
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optical cable for a customer-use to be connected between an outdoor optical cable line and private residence or the like, and especially to an optical cable having good reliability through the elimination of the effects of stress on an optical fiber core of the cable arising as a result of a curving tendency of a tension member of the cable, and to a method for manufacturing thereof.
There have been optical cables for a customer-use consisting of a tension member such as a steel wire and an optical fiber core disposed in parallel and covered with a sheath made of plastic or the like, for example, having the structure shown in
FIG. 4A
(Japanese Unexamined Patent Publications Nos. H.10-010384, H.3-156410).
However, in this kind of optical cables for a customer-use, when the tension member has a curving tendency, if the sheath softens due to being heated to a high temperature by the condition of the environment in which the optical cable was installed, for example, by being exposed under released heat from electrical equipment, the curving tendency of the tension member prevails, and consequently stress acts upon the optical fiber core, and damage such as increased transmission loss or breakage of the optical fiber core occurs.
This phenomenon will now be described specifically, using the drawings.
When the sheath
4
of the optical cable shown in
FIG. 4A
softens by heating, the curving tendency of the tension member
1
may prevail and deformation shown in
FIGS. 4B and 4C
may occur.
When the optical fiber core
2
is pushed to the inner side of the arc of a tension member
1
whose curving tendency has prevailed, as shown in
FIG. 4B
, the optical fiber core
2
suffers stress caused by irregular contracted deformation, and its light transmission loss increases. When the optical fiber core
2
is pushed to the outer side of the arc of a tension member
1
whose curving tendency has prevailed, tension acts on the optical fiber core
2
, causing possible breakage of the optical fiber core.
Typical types of curving tendency of the tension member
1
of an optical cable are shown in
FIGS. 6A
,
6
B and
6
C.
Here, the direction of the curving tendency of the tension member
1
is shown by the direction →R from a tension member
1
a
, whose curving tendency has prevailed in a natural state wherein it is free from constraint by external force, to its center of curvature O, and the degree of the curving tendency is shown by the size of the radius of curvature R. The direction →R of a curving tendency according to this definition is naturally included in the flat plane (hereinafter called the base plain) containing the tension member
1
and the center of curvature O.
The base plain is shown in
FIGS. 6A
,
6
B and
6
C with the reference numerals
200
,
300
and
400
, respectively.
If the curving tendency is the same along the entire length of the tension member
1
, the directions →R of the curving tendencies of all parts of the tension member
1
point toward the same center of curvature O, and their sizes R also take the same value.
When the tension member is wound on a bobbin or straightened under tension or supported by a sheath, this curving tendency is largely constrained by external force and is latent, but when it is freed from external force for example due to the sheath of an optical cable being heated and softening after the cable is installed, the curving tendency prevails and the aforementioned damage occurs.
Hereinafter, except when otherwise indicated, the tension member
1
is referred to in a state such that its curving tendency is constrained by some external force and is completely latent.
The type of curving tendency shown in
FIG. 6A
is such that the optical fiber core
2
is disposed in a flat plane
220
adjacent to and parallel with the base plane
200
containing the tension member
1
and the direction →R and center of curvature O of its curving tendency, and in the position of the tension member
1
as projected perpendicularly onto that plane. The optical cable shown in
FIG. 1
is in the category of the curving tendency type of this FIG.
6
A.
In
FIG. 6A
, the reference numerals
1
,
11
denote the tension member with its curving tendency constrained;
2
,
12
b
the optical fiber core in a state corresponding to that;
1
a
the tension member
1
,
11
with its curving tendency having prevailed; and
2
a
the optical fiber core
2
,
12
b
in a state corresponding to that.
The type of curving tendency shown in
FIG. 6B
is such that the optical fiber core
2
is in a base plane
300
containing the tension member
1
and the direction →R and center of curvature O of its curving tendency, and the optical fiber core
2
is disposed in parallel with the tension member
1
and on the same side thereof as the direction →Ra of its curving tendency. The deformation of an optical cable due to its curving tendency prevailing as shown in
FIG. 4B
is of the category of the curving tendency type shown in this FIG.
6
B.
The type of curving tendency shown in
FIG. 6C
is such that the optical fiber core
2
is in a base plane
400
containing the tension member
1
and the direction →R and center of curvature O of its curving tendency, and the optical fiber core
2
is disposed in parallel with the tension member
1
but on the opposite side thereof from the direction →Rb of its curving tendency. The deformation of an optical cable deforming due to its curving tendency prevailing as shown in
FIG. 4C
is of the category of the curving tendency type shown in this FIG.
6
C.
Optical cables have been manufactured by the kind of method shown in
FIGS. 7A and 7B
. For example, a tension member
1
is given a downward curving tendency by a tension member supply
20
, and is supplied together with an optical fiber
12
b
disposed below it to an extrusion sheathing apparatus. In the extrusion sheathing apparatus, the tension member
1
and the optical fiber
12
b
are integrated by a sheath being formed on them by a crosshead
40
having a die
40
a
with a skittle-shaped opening
40
b
such as that shown in
FIG. 7C
, after which they are taken up on a takeup drum
60
as a completed optical cable.
An optical cable manufactured by this process is of the category of the curving tendency type shown in FIG.
6
B. If either the tension member supply
20
or the die
40
a
shown in
FIGS. 7A and 7B
are vertically inverted, the positional relationship between the curving tendency of the tension member
1
and the optical fiber core
2
is inverted and an optical cable of the category of the curving tendency type shown in
FIG. 6C
is manufactured. Thus, optical cables have normally been of the category of the curving tendency type shown in
FIG. 6B
or FIG.
6
C.
The types of curving tendencies of optical cable shown in
FIGS. 6A through 6C
are merely typical, and an infinite number of types intermediate between these can also exist, depending on the positional relationship between the optical fiber core
2
and the direction of the curving tendency of the tension member
1
. And different curving tendencies can exist in the same optical cable at different positions in the length direction of the optical cable.
When an optical cable has the type of curving tendency of the tension member
1
shown in
FIG. 6B
or
6
C, there is the adverse effects on the optical fiber core
2
as shown in
FIGS. 4B and 4C
due to prevailing this tendency. On the other hand, when an optical cable has the type of curving tendency of the tension member
1
shown in
FIG. 6A
, there is almost no adverse effect on the optical fiber core
2
.
Although it has been possible for an optical cable of related art coincidentally to include the type of curving tendency shown in
FIG. 6A
, the technological ideal of deliberately, actively providing the tension member
1
with this type of curving tendency over the entire length of the optical cable to protect the optical fiber core has not been propose
Ando Kimio
Ishikawa Hiroki
Sera Yuji
Suetsugu Yoshiyuki
Ujiie Seigo
Patel Tulsidas
Sumitomo Electric Industries Ltd.
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