Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
2002-11-18
2004-08-10
Patel, Tulsidas C. (Department: 2839)
Optical waveguides
Optical transmission cable
Loose tube type
Reexamination Certificate
active
06775445
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber drop cable suitable for a FTTH (Fiber to the Home) application, that is, an application where, in order to enable high speed wide band information such as ultra high speed data to be transmitted to and received from even a home or an office, an optical fiber cable extending from a telephone company allows an optical fiber cable core wire to be drawn and wired to a subscriber user such as a usual home and, more particularly, to an improvement over a tensile strength member forming an optical fiber drop cable (external wiring) to be used when drawing an optical fiber to a local home from an electric pole.
2. Description of the Related Art
Referring to
FIG. 1A
, an optical fiber drop cable
101
has a structure which is comprised of an optical fiber core wire
103
(or optical fiber tape-shaped core wire) with a diameter of, for instance, 0.25 mm and a pair of tensile strength members
105
,
105
, composed of conductive metallic wires each including a steel wire with a diameter of, for instance, 0.4 mm, which are disposed along the optical fiber core wire
103
. The optical fiber core wire
103
and the adjacent tensile strength members
105
,
105
are collectively covered with a cable sheath
107
made of thermoplastic resin, such as PVC or fire-retardant PE, to form an optical element section
109
, which is integrally connected to a cable support wire section
115
, serving as a tensile strength member, in parallel thereto via a constricted neck portion
117
, with the cable support wire section
115
including a support wire
111
composed of a metallic wire, such as a steel wire with a diameter of, for instance, 1.2 mm, and covered with a thermoplastic resin sheath
113
such as PVC (polyvinyl chloride) and fire-retardant PE (polyethylene).
Also, as shown in
FIG. 1A
, the cable sheath
107
has both left and right sides formed with notch portions
119
,
119
for cable splicing to take out the optical fiber core wire
103
.
Further, heretofore known optical fiber drop cable of this type is disclosed in Japanese Patent Application laid open Publication No. 2001-83385. As shown in
FIG. 1B
, the fiber drop cable is comprised of an optical element
202
including an optical fiber core wire or an optical fiber tape-shaped core wire
201
and a pair of adjacent tensile strength members T, T composed of conductive metal wires, such as steel wires, respectively, with the optical fiber core wire
201
and the adjacent tensile strength members T, T being covered with a cable sheath S made of thermoplastic resin, and a cable support wire section
203
having a support wire R composed of metal, such as a steel wire, and integrally connected to the optical element section
202
in parallel thereto via a constricted neck portion
204
. Further, the fiber drop cable is structured such that during installation, the support wire section
203
and the optical element section
202
are broken away from one another at the neck portion
205
.
SUMMARY OF THE INVENTION
However, it is feared that not only the optical fiber drop cable
101
previously described but also the other related art optical fiber drop cable encounter accidents, such as burning out of indoor equipments, induced by lightening due to the presence of the conductive metallic wires forming the support wire
111
of the cable support wire section
115
and the tensile strength members
105
,
105
of the optical element section
109
. For this reason, attempts have heretofore been made for either an approach to cut the optical fiber drop cable
101
at the junction closure mounted to an indoor wall surface of the building or the local home to avoid the optical element section
109
from being drawn inside or an approach to cut only the tensile strength members
105
,
105
(steal wires) inside the optical element section
109
, using a specific tool, to allow the optical fiber core wire
103
to be drawn inside the home.
Incidentally, since the cable support wire section
115
is cut at and fixed to the electric pole or the eaves of the local home when drawing the cable support wire section
115
thereto, there is less problem.
In order to improve the deficiencies set forth above, by replacing the conductive metallic material forming the tensile strength members
105
,
105
of the optical element section
109
in question with non-conductive material such as fiberglass, aramid fiber and FRP or the like to form a non-metallic configuration, the above issues may be improved.
Furthermore, with the usual optical fiber drop cable
101
, if there is a low magnitude of adhesive force between the tensile strength members
105
,
105
and the cable sheath
107
, as explained in Japanese Patent Application laid open Publication No. 2000-171673, then the cable
101
undergoes bending and rigorous displacements or the like and, in addition, encounters thermal history such as heat cycles etc., resulting in an increase in optical transmission loss or troubles such as disconnections of the optical fiber core wire
103
encapsulated in the cable.
Accordingly, the adhesive force (extracting force) between the tensile strength members
105
,
105
of the optical element section
109
and the cable sheath
107
forms an important factor in terms of the characteristics of the optical fiber drop cable. But, when manufacturing the above optical fiber drop cable
101
through extrusion forming, a mere technology of extrusion forming the con-conductive material, such as the fiberglass, aramid fiber, FRP (Fiber Reinforced Plastic) or the like, to be used as the tensile strength members
105
,
105
inside the optical element section
109
together with the other members such as the support wire
111
and the optical fiver core wire
103
is hard to obtain an appropriate adhesive force. To increase the above adhesive force, with the invention disclosed in Japanese Patent Application laid open Publication No. 2000-171673, a layer of bonding agent is interposed between the tensile strength members
105
,
105
and the cable sheath
107
. However, the presence of the intervened bonding agent layer results in an increase in manufacturing costs.
The present invention has been made to address such issues mentioned above and has a first object to increase an adhesive force between tensile strength members inside an optical element section and a cable sheath without need for a layer of bonding agent. Further, the present invention provides an optical fiber drop cable, which enables an anti-twist turning property to be improved to avoid an increase in optical transmission loss.
It is a second object of the present invention to provide an optical fiber drop cable that has tensile strength members for an optical element section to be wired to an indoor area of a local home to be structured with non-conductive material of a low cost for avoiding a risk of being struck by lightening while enabling reduction in cost of the cable.
In order to achieve the above objects, an optical fiber drop cable according to a first aspect of the present invention comprises an elongated optical element section having an optical fiber core wire and at least one pair of first tensile strength members, disposed on both sides of the optical fiber core wire in parallel thereto to hold the optical fiber core wire between the first tensile strength members, which are covered with a cable sheath; and an elongated cable support wire section continuously or intermittently adhered to the elongated optical element section in parallel thereto and having a second tensile strength member covered with a sheath; wherein the first tensile strength members includes a collected body of tensile strength fibers made of non-conductive material.
According to the above first aspect, since the first tensile strength members of the optical element section are made of non-conductive material, it is possible to prevent an accident of being struck by lightening. Further more, according to the first aspect,
Kobayashi Kazunaga
Kusakari Masahiro
Miyamoto Matsuhiro
Ohashi Keiji
Tanaka Shimei
Fujikura Ltd.
Patel Tulsidas C.
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