Optical waveguides – Optical transmission cable – Loose tube type
Reexamination Certificate
2002-11-18
2004-09-07
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Optical transmission cable
Loose tube type
C385S106000, C385S113000
Reexamination Certificate
active
06788858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a bundle tube type optical cable, and more particularly, to a bundle tube type optical cable which makes an optical cable bend easily, prevents moisture from penetrating the optical fibers and prevents the optical cable from shrinking in low temperatures by constructing an outer sheath layer enclosing the exterior of a bundle of optical fiber tubes containing optical fibers in the form of a double layer structure consisting of an inner shell made of aluminum material and an outer sheath made of polyethylene.
2. Description of the Related Art
Typically, optical cables are being widely used for transferring electric and electronic signals for TV, computer, telephone and the like. Particularly, they are getting more popularity because they can transfer enormous information rapidly as compared to coaxial cables. However, in respect to such an optical cable, the number of optical fibers to be arranged therein becomes different depending upon its applications, and accordingly there occurs a need for a different structure thereof. For this reason, optical cables having various structures have been developed.
Among them, a bundle tube type optical cable is typical, which is formed in such a manner that at least two optical fiber tubes, each containing two or more optical fibers which are embedded in a longitudinal direction, are arranged in the middle of the optical cable and the cable is wrapped, in sequence from the cable outwards, with a central tube, auxiliary tension wires and an outer sheath layer made of polyethylene. This bundle tube type optical cable can contain a plurality of optical fibers in the optical cable with a small diameter, and so it is economical compared to optical cables with structures of other types. Particularly, since the process of manufacturing the optical fiber tube can be performed along with the process of manufacturing a central tube and other processes of manufacturing an optical cable and also the manufacturing process is simple, it is generally used.
However, in respect to such a bundle tube type optical cable, the optical fiber contained in the optical fiber tube has a small diameter, is weak against any impact, and is particularly apt to be damaged by contact with moisture. Thus, that optical cable must have a structure capable of protecting the optical fiber from moisture and external impact. Also, that optical cable requires bending when connected or depending on the type of ground the cable is buried or disposed under. Because of this, what often occurs is that the optical cable has to be strained, and accordingly the cable itself must have enough elasticity and flexibility. In addition, it is often occurred that such an optical cable is exposed to the external environment, for example, when it is buried and is not affected by a change in temperature. With respect to the physical and mechanical properties, the optical cable must satisfy various requirements. Therefore, a variety of bundle tube type optical cables have been proposed in order to satisfy those requirements.
Referring to
FIGS. 1
to
6
, the structure of a conventional bundle tube type optical cable will now be described.
Firstly,
FIG. 1
is a cross-sectional view showing a bundle tube type optical cable according to a first example of the conventional art, and
FIG. 2
is an enlarged sectional view of an optical fiber tube in the optical cable of FIG.
1
.
As shown therein, the conventional bundle tube type optical cable (A) according to the first example includes: a bundle of optical fiber tubes
6
each containing at least two optical fiber cores
2
; a first water-blocking layer
4
protecting the optical fiber cores
2
in the optical fiber tubes
6
from external moisture by the water-blocking material filled in the inner space of each optical fiber tube
6
; a water-blocking tape
10
enclosing the bundle of optical fiber tubes
6
; a second water-blocking layer
8
protecting the optical fiber tubes
6
from external moisture by the water-blocking material filled between the water-blocking tape
10
and the optical fiber tubes
6
; an outer sheath
14
enclosing the outer surface of the water-blocking tape
10
and protecting the optical cable (A) from external impact; and external tension wires
12
being arranged at a predetermined interval along the length of the outer sheath
14
and having a predetermined tension force.
In respect to the constructed optical cable in the conventional art, the outer sheath
14
is made of polyethylene and the water-blocking material filled in the first and second water-blocking layers
4
and
8
includes jelly or water-blocking powder.
However, the conventional optical cable is provided with no means protecting optical fiber tubes in the outer sheath made of polyethylene, but only the water-blocking tape enclosing the optical fiber tubes. Thus the outer sheath compresses the optical fiber tube to thereby deteriorate the characteristics of the optical fiber core contained in the optical fiber tube. That is, because the conventional optical cable is provided with no means, protecting the optical fiber cores from external impact, excepting the outer sheath made of polyethylene, it cannot protect the optical fiber cores in the optical fiber tube properly and but also may compress the optical fiber tube by the outer sheath itself. As a result, the optical fibers are easily damaged by such pressure.
To solve such problems of the conventional bundle tube type optical cable, there was proposed another conventional bundle tube type optical cable of a different configuration as shown in FIG.
3
.
FIG. 3
is a cross sectional view showing a bundle tube type optical cable according to a second example of the conventional art. The conventional bundle tube type optical cable (A) shown therein, which is employed by Alcatel, has the same structure as the optical cable of the first example as shown in
FIGS. 1 and 2
, except that steel tape
13
is stacked between the water-blocking tape
10
and the outer sheath
14
.
In the conventional optical cable of such a configuration, since the steel tape
13
having a high strength is arranged between the water-blocking tape
10
and the outer sheath
14
and protects the optical fibers from external impact and compression from the outer sheath, this optical cable can solve the problems of the optical cable of the first example. But, the optical cable of this example must have bending properties such as proper elasticity and flexibility. However, in the optical cable of such a structure, the strength of the steel tape is extremely high and accordingly there still exists a problem that such bending properties are deteriorated if not carrying out the process of forming a corrugation. Moreover, for forming the steel tape well, it must be bonded by a hot melt adhesive, which makes the manufacturing process complicated and increases the manufacturing cost.
FIG. 4
is a cross sectional view showing a bundle tube type optical cable according to a third example of the conventional art.
The bundle tube type optical cable of the third example as shown in
FIG. 4
, which is being employed by Lucent Technology, has a similar structure to the second example illustrated in FIG.
3
. That is, that optical cable has the same structure as the optical cable of the first example as shown in
FIGS. 1 and 2
, except that a plastic tube
15
and steel tape
13
are stacked between the water-blocking tape
10
and the outer sheath
14
.
However, the optical cable of such a configuration cannot solve the problems also occurring in the second example too. Moreover, the plastic tube is enclosed with the steel tape after forming the plastic tube around the optical fiber tube, which makes manufacturing more complicated and increases the manufacturing cost.
FIG. 5
is a cross sectional view showing the structure of a conventional bundle tube type optical cable according to a fourth example of the conventional art.
The optical cable as shown in
FIG.
Ahn Jin-cheol
Ahn Yon-soo
Lee Byung-gon
Park Euy-don
LG Cable Ltd.
Nath & Associates PLLC
Novick Harold L.
Palmer Phan T. H.
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