Optical fiber cable with fiber enclosing tubes in transparent core

An optical fiber cable with an elongated core of transparent plastic material having a plurality of readily visible tubes of a dull material embedded therein and extending longitudinally thereof. Each tube loosely receives at least one optical fiber. The core has a plurality of grooves at the outer surface thereof which extend parallel to the paths of the tubes and which are spaced from the tubes, and the grooves have a hydrogen retaining material therein. Each groove is on a radial line intermediate pairs of tubes.

The present invention relates to an optical fiber cable of the type 
comprising, inside a sheath, a core of plastic material embedding small 
tubes which extend longitudinally of the cable and contain optical fibers 
in loose condition. 
Cables of such type are already known and are, for example, described in 
U.S. Pat. Nos. 3,865,466 and 4,191,448. Such known cables have the 
following disadvantages. 
A first disadvantage is the impossibility of diverting optical fibers from 
the cable without completely interrupting its continuity. In fact, once 
the cable sheath is removed from the cable region where an optical fiber 
shunt is to be provided, it is not possible to locate the tubes containing 
the optical fibers. The only way of locating the tubes is to cut the cable 
completely along a plane perpendicular to the longitudinal axis of the 
cable. 
It follows that, in such known cables, whenever it is desired to make a 
connection to one of the optical fibers contained in one of the tubes, it 
is necessary to cause a discontinuity in all the cable components, and 
consequently, also in the tubes and in the optical fibers not involved in 
the connection and then, to restore said continuity between the cable 
elements and, in particular, between the other tubes and the optical 
fibers not involved in the connection to one of the fibers. 
This operation, besides being extremely complicated, involves the risk of 
causing damage to the cable, such as, for example, the risk of causing 
attentuation of the signals transmitted by the optical fibers not involved 
in the connection, due to incorrectnesses in the performance of the 
connections effected to restore the cable continuity. 
A further drawback of the known cables of this type is a limitation in the 
selection of the substances, able to absorb permanently any trace of 
hydrogen and which may have been introduced in the cable to protect the 
optical fibers against the harmful action which hydrogen might have on 
them. 
Within the sheath of such cables, the space available for the admission of 
substances able to absorb hydrogen is only the small tubes containing the 
optical fibers. 
Therefore, the optical fibers are necessarily in direct contact with the 
substances which must permanently retain hydrogen to prevent the latter 
from damaging said optical fibers. 
The direct contact between the optical fibers and the substances able to 
absorb hydrogen leads to the exclusion of those substances, the presence 
of which might damage the optical fibers. 
For example, it is impossible to use in the conventional cables of this 
type those substances which are able to absorb hydrogen and which contain 
granules of material having a size over 10 microns, since these granules, 
hindering the free motion of the optical fibers inside the small tubes, 
would cause microbendings in the fibers with consequent impairment 
thereof. 
The main object of the present invention is to provide an optical fiber 
cable which does not have the above-described disadvantages and which 
allows simple and reliable performance of connections to the optical 
fibers of the cable without the risk of causing damage to the latter as 
well as the introduction, without any limitation as to its selection, of 
any substance able to retain traces of hydrogen or relevant amounts of the 
same in order to protect the optical fibers against the prejudicial action 
which hydrogen might have on them. 
The preferred embodiment of the present invention is an optical fiber cable 
which comprises a sheath enclosing a core of plastic material embedding at 
least one small tube which extends longitudinally of the core and which 
loosely contains at least one optical fiber, the cable being characterized 
in that the core is made of transparent material wherein the small tubes 
are made of a material which is readily visible through the material of 
the core, such as a low reflecting or colored material, and in that the 
radially outermost surface of the core is provided with recesses extending 
along the core in a direction parallel to the paths of the small tubes, at 
least one recess being provided in each region of said core which is 
between adjacent small tubes.

With reference to the drawing, the cable therein illustrated comprises, 
from the inside to the outside, a strand 1, formed by stranding together a 
plurality of wires 2 made of a material having high mechanical 
characteristics, such as, for example, steel, an aromatic polyamide, nylon 
and the like, which occupies the radially innermost portion of the cable. 
In particular, said strand 1 has dimensions which enable it to withstand 
the mechanical stresses to which the cable is subjected during its 
manufacture and laying. 
A core 3 of transparent plastic material is applied around strand 1 and the 
tubes 4, preferably, by means of an extrusion process. 
A significant feature of said core 3, for the purposes of the present 
invention, is that it can be made of any transparent plastic material. In 
this specification, the term "transparent", as it refers to the material 
forming the core 3 of a cable, means any material through which the 
elements embedded in the core 3 can be clearly seen or simply located. 
Examples of transparent plastic materials which can be used to form the 
cable core 3 are polyethylene, polypropylene and nylon. 
The cable core 3 embeds the small tubes 4 which loosely contain at least 
one optical fiber 5. The small tubes 4 shown in the drawing have, in 
section, a circular shape, but other cross-sectional shapes can be used. 
The tubes 4 extend longitudinally of the core along a helical path which 
can be of a closed or of an open type, the latter term meaning that the 
helix is formed by alternating S-shaped or Z-shaped portions. 
An essential feature of the present invention is that the small tubes 4 are 
made of a material which is readily visible through the material of the 
core 3. Generally speaking, they will be made of a dull material which, as 
used herein, means a material having color or reflectivity characteristics 
which makes the tubes 4 visible through the transparent material of the 
core 3. Examples of dull material from which the small tubes 4 can be made 
are metallic materials and plastic materials of any type which are colored 
with inorganic pigments. 
Preferably, the small tubes 4 of the cable are differently colored to 
permit distinguishing one tube 4 from another tube 4. 
The core 3, at its radially outermost surface, is provided with grooves 6 
which extend longitudinally of the core 3 and follow a path identical in 
shape to that of the small tubes 4 embedded in the core 3. Said grooves 6 
which, in a section perpendicular to the cable axis, preferably are 
wedge-shaped, are provided in a number at least equal to the number of 
small tubes 4 embedded in the core 3 and at least one groove is present in 
each portion of said cable core 3 between adjacent small tubes 4. 
The grooves 6 are filled with any substance capable of retaining, in a 
permanent way and either physically or chemically, both traces and 
relatively large amounts of hydrogen so as to ensure that the hydrogen 
cannot reach the optical fibers 5 loosely contained in the small tubes 4 
and thereby damage them. 
Substances able to carry out such function are, for example, the powders of 
metallic elements able to physically absorb hydrogen are known and can be 
those substances described in U.S. Pat. No. 4,718,747. 
Alternatively, and still by way of example, substances able to carry out 
such function are the compositions suitable to react chemically with 
hydrogen, such as those described in U.S. Pat. Nos. 4,688,889; 4,725,122; 
4,725,123 and 4,741,592. 
A sheath 7, made for instance of metallic or plastic material and closing 
recesses 6, is provided around the cable core 3. 
The cable described herein and illustrated in the drawing represents only 
one specific embodiment of a cable according to the invention, but the 
cable of the invention can have other structure provided that it has the 
following characteristics: 
(1) The cable core is made of transparent plastic material and has embedded 
therein small tubes of dull material loosely containing the optical 
fibers; and 
(2) The radially outermost surface of the cable core is provided with 
grooves extending longitudinally of said core (preferably along paths 
identical to the paths of the small tubes) which contain a substance able 
to retain permanently both very small traces and relatively large amounts 
of hydrogen. In any cable according to the invention, at least one groove 
is present in each portion of the cable core disposed between pairs of 
adjacent small tubes. 
A cable of the present invention may also differ from the cable illustrated 
in the drawing only in the omission of the strand 1. 
From the foregoing description and from the considerations set forth 
hereinafter, it will be apparent that the cables according to the 
invention achieve the objects of the invention. 
In fact, the presence in a cable of a core of transparent plastic material 
in which small tubes of dull material are embedded, and particularly if 
the tubes have different colors, provides the possibility, when the sheath 
7 is removed from the cable, to locate immediately the position of the 
small tubes, thereby avoiding the need, as with the prior art cables, of 
performing a complete cutting of the cable to locate the small tubes it 
contains. 
Said immediate location of the small tubes inside the cable core leads to 
the possibility, when a connection concerning the optical fiber or fibers 
contained in one small tube is to be effected, of separating only the 
portion of cable core containing said one small tube and of effecting only 
on it the operations required for the connection without being compelled 
to act on all the other cable components and, consequently, on the other 
small tubes and optical fibers contained therein. 
Consequently, there is no risk of causing damage to the cable components, 
particularly the other fibers during the performance of a connection. 
Further, the fact that the outer surface of the cable core is provided with 
grooves which have paths identical in shape to the paths of the small 
tubes and which, in pairs, are arranged side-by-side with respect to the 
individual small tubes, facilitates the separation from the cable of core 
portions containing only one small tube. 
In fact, said grooves constitute a guide for any blade used to effect cuts 
in the core parallel to one small tube to be able to separate it from the 
others contained in the cable. 
Moreover, the grooves, flanking in pairs the individual small tubes 
containing the optical fibers, provide the possibility of introducing into 
them any known substance able to retain hydrogen and of ensuring an 
efficient protection of the optical fibers. 
In this way, it is not necessary, as in known cables, to limit the 
selection of the substance able to retain hydrogen permanently since, in 
the cable according to the invention, these substances are not in direct 
contact with the optical fibers and, therefore, cannot exert onto them any 
negative effect. 
Although preferred embodiments of the present invention have been described 
and illustrated, it will be apparent to those skilled in the art that 
various modifications may be made without departing from the principles of 
the invention.