Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
2002-02-19
2004-11-30
Hyeon, Hae Moon (Department: 2839)
Optical waveguides
Optical transmission cable
Loose tube type
C385S105000, C385S112000
Reexamination Certificate
active
06826338
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber cable (hereinbelow, referred to as “optical cable”), in particular, an optical cable employing plastic optical fibers.
2. Discussion of the Background
Optical fibers have been widely employed to transmit high volume of information fast and reliably in recent communication. The optical fibers include silica optical fibers, such as silica single-mode optical fibers, plastic optical fibers (POF) and other fibers. In particular, the plastic optical fibers have a larger diameter than the silica single-mode optical fibers and are excellent in flexibility. From this viewpoint, the optical cables, which employ plastic optical fibers has optical transmission lines, are excellent in workability in end treatment and connection treatment of the optical fibers needed during installation, and in wiring. The optical cables are effective as a short distance trunk in a building after lead-in from a trunk cable, a branch cable, or a line cable for a Local Area Network (LAN) system.
The optical cables are usually configured to cover optical fibers and tensile strength reinforcing members (tension members) for avoiding elongation of the optical fibers due to tension with a sheath. In general, the optical fibers have a primary resin covering applied on a surface to prevent disturbance light from entering, to avoid damage due to a mechanical external force, or for another reason. In the case of optical cables for communication, two or more optical fibers for both input and output are usually housed.
One of the optical cables comprises optical fibers
41
a
and
41
b
, primary covering layers
42
a
,
42
b
for covering the optical fibers, and a secondary covering layer
43
for covering the optical fibers as shown in FIG.
4
(
a
) for instance (see, e.g., JP-A-11-211954).
The optical cable shown in a schematic sectional view of FIG.
4
(
b
) has a structure wherein two optical fibers
44
a
and
44
b
are provided in a cavity
46
delimited by a sheath
45
, and tensile strength reinforcing members are embedded in the sheath (see, e.g., JP-U-60-60714).
The light cable shown in a schematic sectional view of FIG.
4
(
c
) has a structure wherein an optical fiber
48
having a surface covered with a primary covering layer
47
is arranged in a cavity
50
delimited by a sheath
49
(see, e.g., JP-A-7-72356).
However, the optical cables that have been proposed or used have raised the following problems:
1) In the cable having the structure shown in FIG.
4
(
a
), a heat test (at 70° C. for 24 hours) shows that a resin, such as polyethylene, as the covering material is heat-shrunk to form microvents in the surfaces of the optical fibers, which create a problem of resistance to heat in terms of an increase in attenuation.
2) In the cable having the structure shown in FIG.
4
(
b
), the provision of the plural optical fibers in a single cavity creates a problem of resistance to pressure that, when an external force, which is caused, e.g., when a person steps on the cable, is applied to the cable, the plural optical fibers in the single cavity get in contact with each other, are pressed each other, be squashed each other at the worst, or are subjected to plastic deformation to increase attenuation.
3) In the cable having the structure shown in FIG.
4
(
c
), an increase in attenuation, which is caused by flexing action during bending, can be suppressed by determining the unoccupied ratio of the optical fiber in the cavity at 2-30%. However, there is created a problem of mechanical properties, such as an impossibility in avoiding an increase in attenuation to flexing action during bending since the upper limit of the unoccupied ratio is restricted in terms of connection with an optical connector, which is required when the optical cable is connected to the optical connector.
In particular, a graded refractive index plastic optical fiber (hereinbelow, referred to as “GI-POF”), which is prospective as an optical fiber for next-generation communication because of a fast and large volumetric data-carrying capacity, realizes a fast and large volumetric data-carrying capacity by having a refractive index distribution in a sectional direction of the fiber. An optical cable that houses a GI-POF is sensitive to generation of microvents caused by heat-shrinkage of a covering material, application of an external force, flexing action during bending or other factors, and transmission properties are likely to be deteriorated by these disturbances.
The production of an optical cable having a GI-POF is carried out by covering and molding a GI-POF and a structural element, such as a tension member, for protection against tension with, e.g., an extruded thermoplastic resin. There is a possibility that a low molecular chemical compound in the GI-POF is thermally defused by thermal affection from, e.g., the thermoplastic resin molten at a high temperature to change the refractive index distribution of the GI-POF during the production. From this viewpoint, it is necessary to carry out the production so that the GI-POF is not thermally affected during covering and molding.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical cable excellent in resistance to heat and mechanical properties to flexing action, and capable of preventing attenuation from increasing.
The present invention provides an optical fiber cable comprising two or more optical fibers and a partitioning spacer housed in a space encircled by a sheath; the partitioning spacer including an axial portion and a plurality of partitioning plate portions; the partitioning spacer having a sectional shape that the partitioning plate portions radially extend toward an inner circumferential surface of the sheath from the axial portion; and each of the partitioning plate portions having a leading end provided with an enlarged portion in contact with the inner circumferential surface of the sheath and a connecting portion connecting the enlarged portion to the axial portion; wherein the space encircled by the sheath is divided into a plurality of partitioned slots by the partitioning plate portions, and the respective optical fibers are distributed so that two or more optical fibers are not provided in a single partitioned slot.
It is preferable that the sectional shape of the partitioning spacer has the following relations (1) and (2) wherein each of the enlarged portion has a maximum dimension L in a direction perpendicular to a radial direction, each of the connecting portion has a length K in the radial direction, each of the connecting portion has a dimension W in the direction perpendicular to the radial direction, and each of the optical fibers has an outer diameter R:
L−W≧R
(1)
K≧R
(2)
The optical fiber cable is appropriate as a cable with graded refractive index plastic optical fibers (GI-POF) employed therein.
It is preferable that at least one tension member is provided in a partitioned slot without an optical fiber provided therein. At least one of a power line and an information transmission line may be provided in a partitioned slot without an optical fiber provided therein.
It is preferable that the sheath has a hardness of not higher than 95 Shore A hardness. In this case, it is preferable that the sheath is made of thermoplastic resin, and the thermoplastic resin is one selected from soft vinyl chloride, chlorinated polyethylene and soft polyethylene.
The present invention also provides a method for preparing the optical fiber cable stated earlier, comprising distributing the optical fibers in the partitioning spacer, and then forming the sheath by thermoplastic resin extruded from a resin extruder. In the method, it is preferable that the partitioning spacer is heat-treated under a thermal environment at 70-90° C. before preparation of the optical fiber cable.
An optical fiber to be accommodated in the optical cable according to the present invention is a bare optical fiber or an
Asahi Glass Company Limited
Hyeon Hae Moon
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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