Method of forming an optical waveguide with a reinforced protective covering

A method for covering at least one optical fiber with a protective layer comprises extruding the protective layer and embedding reinforcing elements in the protective layer to form a composite covering and simultaneously introducing the optical fiber into the composite covering. The method includes introducing a single waveguide or a plurality of waveguides, which may be formed into a bundle with a filling compound.

BACKGROUND OF THE INVENTION 
The present invention is directed to a method for covering at least one 
optical waveguide with a protective layer and for applying reinforcing 
elements. In particular, the invention is directed to a method for 
covering at least one optical waveguide with a protective covering which 
surrounds the optical waveguide on all sides and is applied by extrusion 
together with reinforcing elements embedded in the covering. 
DE-OS 39 00 901 discloses a method in which reinforcing elements are 
extruded in the form of threads from individual nozzles of an extruder, 
which nozzles are arranged around the periphery of a circle surrounding a 
bore. An optical waveguide, which is provided with a coating, is fed 
through a bore of the extruder head. In a subsequent stranding process, 
the reinforcing threads are applied with alternate directions of lay to 
the coating of the optical waveguide. An additional coating is then 
applied by means of another extruder. The reinforcing thread, thus, lies 
in a closed layer below the outer jacket or protective coating, which 
surrounds the whole structure. There is not a particularly strong bond 
between the outer protective covering and the underlying reinforcing 
threads so that a substantially two-layer structure results wherein both 
layers are independent of each other. Another disadvantage of this known 
method is that the threads consisting of liquid crystal polymers (LCP) or 
similar tension-resistant materials must be applied in an individual 
stranding process to the relatively thin and, therefore, sensitive optical 
waveguide, which has only been provided with one coating layer. 
SUMMARY OF THE INVENTION 
The present invention is directed to providing a method for covering an 
optical waveguide in a particularly simple manner, which optical waveguide 
has particularly good mechanical properties. The present invention 
provides a method of covering the optical waveguide with a protective 
covering having embedded reinforcing elements with the covering 
surrounding the optical waveguide. The method comprises the steps of 
forming a composite element comprising the protective covering and the 
embedded reinforcing elements in a coextrusion process and introducing the 
optical waveguide into the composite element during the coextrusion 
process. 
Since the protective covering and the reinforcing elements embedded therein 
are manufactured together in a single working process, namely by 
coextrusion, only one extruder tool is required and the protective 
covering is manufactured together with the reinforcing elements in this 
stage of the method. Since the reinforcing elements are embedded directly 
into the protective covering during the manufacturing process and a tight 
connection results therebetween, they form a composite element which has 
high tensile strength, since the protective covering, on the one hand, and 
the reinforcing elements, on the other hand, are homogeneously connected 
to each other. This composite element, acting from the outside inward as a 
uniform layer, is applied with a tight fit on the optical waveguide. Thus, 
the optical waveguide is provided with a protective jacket, which is 
highly effective against traction or tensile forces. 
Another aspect of the present invention provides an apparatus for covering 
an optical waveguide with a protective covering having embedded 
reinforcing elements. The apparatus includes an extruder head having a 
bore, an annular gap for extruding material of the protective covering 
surrounding the bore and nozzles for the extruding material of the 
reinforcing elements with the nozzles being disposed in a circular 
arrangement within the annular gap. 
The present invention also provides an optical waveguide with a protective 
covering extruded thereon in which the protective covering contains 
embedded coextruded reinforcing elements and the material of reinforcing 
elements has a higher tensile strength than the material of the protective 
covering. 
Another aspect of the present invention provides an optical cable with at 
least one buffer fiber in which the buffer fiber has a protective covering 
into which coextruded reinforcing elements and the material of the 
reinforcing elements has a higher tensile strength than the material of 
the protective covering.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The principles of the present invention are particularly useful when 
incorporated in a device illustrated in FIG. 1 to manufacture an optical 
waveguide with a fixed core LA, as illustrated in FIG. 3. 
The device or apparatus for forming the optical waveguide fixed core LA, as 
shown in FIG. 1, includes a supply coil VS from which the optical 
waveguide LW, which is provided with a protective coating, is withdrawn. 
The optical waveguide LW, as seen from the cross sectional presentation of 
FIG. 3, consists of an optical fiber LF consisting of a core and jacket 
material, as well as a single-layer or multi-layer protective coating CT, 
which is applied directly after the manufacturing process for the optical 
fiber LF. The optical waveguide LW is introduced into a bore BO of an 
extruder head, generally indicated at EX. The extruder head EX has an 
annular nozzle RD at its exit point, as shown on the right hand side in 
FIG. 1, and as illustrated in FIG. 2, and a first material is extruded 
through the nozzle RD to form the covering SH. The first material MA1 is 
selected from a group consisting of a high density polyethylene (HDPE), a 
low pressure polyethylene of low density (LLDPE), a polyethylene of 
average density (MDPE), a polycarbonate (PC), a polyamide (PA), a 
polybutylene terephthalate (PBT), a mixture of polycarbonate and 
polybutene terephthalate, polyphenylene sulphide (PPS), polyvinyl chloride 
(PVC), polyurethane (PUR), FRNC (flame retardant non corrosive) mixtures, 
polyetherimide (PEI), polytetrafluoroethylene (PTFE), 
ethylene/tetrafluorethylene (E/TFE), 
tetrafluorethylene/hexafluoropropylene (FEP) and a polyamidimide (PAI). 
Also, mixtures of the named materials are possible, wherein generally it 
can be said that it is preferable to use polymer materials which can be 
easily extruded and which also satisfy the other requirements for covering 
of the optical waveguides. 
Distributed over the circular annular gap of the nozzle RD are provided 
individual nozzles DS1 to DSn (best illustrated in FIG. 2). Nozzles DS1 to 
DSn are arranged so that the material MA1 of the protective covering SH 
will flow around the nozzles on all sides. These nozzles, such as DS1, are 
separated from the flow of the covering material MA1 by the schematically 
indicated wall WD1 and WD2 and the material MA2 flows between the walls 
WD1 and WD2 of the nozzle DS1, for example, thus, generates a reinforcing 
element VE1. Each reinforcing element formed in this way, as illustrated 
in FIG. 3, correspondingly is embedded in the protective covering SH and 
these elements are surrounded on all sides by the material of the 
protective covering SH. With a circular structure of the nozzle opening 
correspondingly circular formations of the reinforcing elements VE1 
through VEn, according to FIG. 3, are produced. It is also possible to 
select other, for example rectangular, cross sectional segments forms for 
the nozzle openings DS1 through DSn. 
A stretch cone RK (see FIG. 1) produced by the coextrusion is stretched 
downward while still in the soft state onto the optical waveguide LW 
corresponding to the direction of travel from left to right. The structure 
illustrated in FIG. 3 is, thus, produced. The optical waveguide fixed core 
LA, in addition, is provided outside the coating CT with a composite 
element SV comprising strands VE of material MA2 embedded in a layer SH of 
material MA1. The protective covering SH with the embedded reinforcing 
elements VE1 sits in this example firmly on the coating CT. 
Polycarbonates or liquid crystal polymers can be used as the material for 
the reinforcing elements VE1 through VEn. Due to the stretching process in 
the region of the stretch cone RK, these obtain the necessary orientation 
of their molecules and, therefore, the high tensile strength of this 
material. It is also possible to embed other high strength materials as 
reinforcing elements VE1 through VEn into the material of the protective 
covering SH, wherein advantageously the E-modulus of these elements should 
have 2 to 20 times the E-modulus of the material of the protective 
covering. Furthermore, in this context, the use of thermoplastics 
reinforced by threads as material MA2 is possible, wherein short fiber 
pieces can be embedded into the material MA2, these fiber pieces 
consisting of tension resistant glass fibers or carbon fibers or whiskers, 
for example. These fiber pieces of glass, metal or the like, 
advantageously should be selected to be longer than the diameter of the 
reinforcing elements VE1 through VEn in order to assure that these 
fiber-shaped elements are, in each case, embedded in the longitudinal 
direction of the reinforcing elements or are correspondingly aligned in 
the extrusion process. The length of these threads or fibers should, 
advantageously, be selected between 0.2 mm and 1.0 mm, and their diameter 
selected to be between 0.5% and 2.5% of the outer diameter of the 
reinforcing elements VE1 through VEn illustrated in FIG. 3. 
In the embodiment according to FIG. 3, the composite element SV is firmly 
connected to the optical waveguide LW by being glued together, for 
example. This may be achieved when the plastic material of the coating CT 
and the plastic material of the protective covering SH form a homogeneous 
bond with each other. It is, however, possible, for example, to apply a 
fusion adhesive SK to the optical waveguide LW in a thin layer and, thus, 
to produce a solid bond between the composite element SV and the coating 
CT of the optical fiber core LW. For application of the fusion adhesive 
SK, the device SKE according to FIG. 1 can be used. Due to the high 
tensile strength of the composite element VS, a frictional lock connection 
between this composite element VS and the optical waveguide LW is normally 
possible without the optical waveguide being impaired, for example, by 
high tensile stresses. 
If, however, particularly strong tensile stresses or other mechanical 
stresses occur, then it can be advantageous to provide a thin gap between 
the optical waveguide LW and the protective covering SH, which would occur 
in the exemplary embodiment according to FIG. 3 at a location of the 
fusion adhesive SK. This thin gap can be filled with a coupling medium, 
which can be formed, for example, of air of other slidable material, so 
that the traction forces which act on the protective covering SH are not 
transmitted directly to the waveguide LW. The width of this gap should be 
selected between 1 .mu.m and 60 .mu.m, wherein the preferred range of 
between 5 .mu. and 15 .mu.m can be used. It is advantageous to use a 
coupling medium, which has thixotropic properties, for example, so that 
when there are shear forces, a liquifying of the coupling medium occurs in 
the correspondingly stressed region and the force transmission from 
outside to the optical waveguide LW can be kept particularly low. It is 
also possible, therefore, to use a rubber elastic, for example very soft, 
material as a coupling medium filling the gap, wherein the thickness of 
the layer is advantageously between 5 .mu.m and 50 .mu.m. 
Advantageously, the reinforcing elements VE1 through VEn determine the 
physical properties of the composite element SV and are made of a material 
with a heat expansion coefficient corresponding approximately to that of 
the optical fiber LF according to FIG. 3. This requirement can preferably 
be realized by use of an LCP material for the reinforcing threads VE1 
through VEn, because LCP material has a low coefficient of heat expansion 
in the region of -10.sup.-7 to +10.sup.-7 and with a corresponding 
selection of the stretching can be brought close to that of around 5.5 . 
10.sup.-7 for the light fiber LF. 
The outer diameter of the optical fiber LF equipped, according to the 
invention, with the composite element SV, should approximately be 1.5 to 8 
times the outer diameter of the optical fiber LF. Such dimension allows 
further processing, for example the stranding and cabling with the usual 
machinery in the traditional cable technology. 
It can also be advantageous to coat the optical waveguide LW or the optical 
fiber LF with a lubricant, for example talcum, in order to improve the 
packaging. Thus, unrolling potential of the reinforcing casing will be 
improved. 
The reinforcing elements VE1 through VEn are advantageously made of a 
material with an E-modulus which is greater than 5000N/mm.sup.2. In 
contrast, it is sufficient for the material MA1 of the protective covering 
SH if this has an E-modulus greater than 200N/mm.sup.2. 
From the overall cross sectional area of the composite element SV according 
to FIG. 3, only between 4% and 20% of the surface area needs to be filled 
by the reinforcing elements VE1 through VEn. The proportion of the 
reinforcing elements VE1 through VEn is kept low on the overall cross 
sectional area of the composite element SV. 
The reinforcing elements VE1 through VEn should, advantageously have a 
diameter which is selected to be approximately between 10% and 70% of the 
outer diameter of the bare optical fiber LF. 
It is also possible to provide several layers of reinforcing elements, as 
represented in FIG. 4. In this process, the outer layer with the elements 
VE21 to VE2n are advantageously designed with a greater diameter than the 
inner layer VE11 to VE1 n. The greater diameter of the outer layer should 
improve the buckling strength when there are bending stresses. 
The subsequent exemplary embodiments illustrate the application of the 
inventive thought for the manufacture of buffered fibers, for example an 
arrangement in which several optical fibers are arranged in the interior 
of a protective covering. In the device shown in FIG. 5 for manufacturing 
such buffered fibers, several supply coils VS1 through VSm are provided 
and they have optical fibers LW1 through LWm, which are provided with a 
protective layer coating. 
These optical waveguides LW1 to LWm are removed and supplied to a filling 
device FE, by means of which the optical waveguides LW1 through LWm are 
embedded in a filling compound FC. The optical waveguides are arranged 
with a greater distance from each other than visible from the cross 
sectional representation of FIG. 6 and are loose, that is embedded to a 
certain extent in a mobile or displaceable manner in the filling compound 
FC. The pasty material can be used for the filling compounds SC, in 
particular materials with thixotropic properties and, possibly, with an 
oil addition. In each case, the viscosity of the filling compound FC 
should be selected so that the optical waveguide bundle covered with the 
filling compound FC can be led through the bore BO of the extruder EX 
without dripping off. The extruder EX has a similar construction to the 
embodiment illustrated in FIGS. 1 and 2 and, therefore, the same reference 
numerals are used for the same parts. Also, the supplied materials MA1 and 
MA2 have the properties or compositions described in connection with FIG. 
1, described hereinabove. However, the diameter of the annular nozzle RD 
is selected to be correspondingly greater than the embodiment according to 
FIGS. 1 and 2, and also the gap width of this annular nozzle is to be 
widened corresponding to the altered requirement approximately relative to 
this arrangement. 
The stretch cone RKB produced by the extruder EX is pulled down onto the 
filling compound bundle FB containing the optical waveguide, which 
essentially lie tightly one this, as seen in the cross sectional drawing 
of FIG. 6. The nozzle for the generation of the tension-proof elements VB1 
through VBn, for example DS1, are arranged with the circular cross section 
in a similar manner to the nozzles DS1 to DSn according to FIG. 2. 
Therefore, corresponding circular reinforcing elements VB1 through VBn are 
also produced with the exemplary embodiments according to FIG. 6. The 
resulting optical buffered fiber OB, thus, contains a high tensile outer 
covering because of the reinforcing elements VB1 through VBn so that the 
optimum protection for the optical waveguides LW1 through LWn located in 
the interior is achieved. These optical waveguides can be produced with 
corresponding overlengths and can be accommodated in alternating positions 
in the interior of the protective covering SHB representing the composite 
elements. In addition, it is possible also for the waveguides to be 
loosely stranded or twisted with each other. The inner opening of the 
protective covering SHB is selected so that its cross section is, in each 
case, substantially greater than the overall cross section of the optical 
waveguides LW1 to LWm contained in it. The reinforcing elements VB1 
through VBn are firmly embedded in the material of the protective covering 
SHB and produced together with this a connecting construction SVB with 
properties similar to those of the covering SH, which have been 
illustrated already with the aid of FIGS. 1-4. 
In FIG. 7, an exemplary modification is illustrated wherein two layers 
VBL71 and VBL72 of reinforcing elements are introduced into the protective 
covering SHB7. The outer layer VBL71 of these reinforcing elements lies on 
an assumed circle, which has a diameter that is greater than the circle 
for the layer VBL72 of the reinforcing elements that lies as an inward 
layer. Moreover, the reinforcing elements of the outer layer VBL71 and 
that of the inner layer VBL72 are arranged in each case in a staggered 
relationship with each other. In addition, it is provided that the 
elements of the outer layer VBL71 can be produced with a greater diameter 
than the tension-proof elements of the inner layer VBL72. This has the 
advantage that the covering is particularly rigid against buckling and can 
also absorb high compression forces. 
FIG. 8 shows another exemplary embodiment having an outer layer VBL81 of 
approximately band-shaped reinforcing elements, which are embedded in the 
protective covering SHB8. The band-shaped reinforcing elements extend 
approximately in the peripheral direction on an assumed circle. In 
addition, tensile-proof elements with an approximately star-shaped cross 
section are arranged on the inner layer VBL82. The elements of both layers 
VBL81 and VBL82 are also arranged staggered relative to each other. It 
should be pointed out that the cross sectional shape of these elements are 
formed by the cross section of the respective nozzle, such as DS1. 
In the previous exemplary embodiments illustrated in FIGS. 5-8, the 
reinforcing elements have been introduced, in each case, in an even 
arrangement. A buffered fiber OB9 of FIG. 9 has reinforcing elements, for 
example VBL9, which can be in an uneven distribution over the cross 
section of the protective covering SHB9. 
FIG. 10 shows an exemplary embodiment of an optical buffered fiber OB10 in 
which the reinforcing elements, for example VB10, are seen in a 
longitudinal direction of the cylindrical protective covering SHB10 and 
extend approximately in a spiral shape. Such an arrangement can, for 
example, be produced in that the injection head, according to FIG. 5, is 
offset in rotation about the axis of the bore BO, so that the continuous 
extrusion produces spiral-shaped extending reinforcing elements VB10. 
If optical waveguide strips or bands are arranged on the supply coils VS1 
through VSm, of the device of FIG. 5, these supply coils, for example, are 
arranged in carriage rotating in the same direction, preferably 
synchronous, so that a strip stack BST, which is formed by the optical 
waveguides strips or bands LB1 through LBp, will be twisted in a spiral 
shape in the interior of the protective covering SHB10. The rotation of 
the protective covering SHB10 occurs in the plastic state, and mainly in 
the region between the extruder head and the subsequent cooling trough. 
The rotation of the strip stack BST occurs through friction between the 
protective covering SHB10 and the strip stack, wherein the filling 
compound FC possibly functions as a carrier. 
The optical buffered fibers corresponding to the embodiments of FIGS. 5-10, 
for example, form the core element of an optical cable. With the 
correspondingly strong formation of the protective covering, it is 
frequently not necessary to apply additional outer jackets. That is, the 
protective covering SHB to SHB10 containing the reinforcing elements 
practically represents the cable jacket at this stage. It is, however, 
also possible, as shown in FIG. 9, with corresponding particular 
requirements to provide the buffered fiber OB9 with additional outer 
layers, for example an inner jacket IM9 and an outer jacket AM9. Possibly, 
also, a layer jacket with an embedded metal band or foil ME9 can be 
applied in order to prevent water vapor diffusion on the optical cable OC9 
obtained in this manner. 
In addition to arrangements often called "maxi bundle" cables, with only 
one optical bundle, there is also the possibility of stranding several 
such optical buffered fibers SHB to SHB10, which are illustrated in FIGS. 
6-10 to form a core of an optical cable. Then, a corresponding jacket is 
applied outside on this cable, which jacket can possibly also be formed in 
multi-layers. One particular embodiment of such an arrangement is shown in 
FIG. 11, where four optical buffered fibers OB111 through OB114 are 
stranded together and together form a cable core of an optical cable OC 
11. Each of these optical bundles OB111 through OB114 has a protective 
covering SH111 to SH114 into which the tension-proof elements VB111 to 
VB114, respectively, have been embedded in a great number. For optimum use 
of the cross section of the cable core, the optical bundles OB111 to OB114 
are provided with an approximately sector-shaped cross section and are 
packed with their sector-shaped faces or surfaces directly on each other, 
for example combined by stranding. In this way, a high tensile core 
construction can be obtained, even with the relatively thin wall 
thicknesses of the individual protective coverings SH111 to SH114 and, 
because the packed reinforcing elements VB111 to VB114, each of these 
bundles is particularly tension-proof and resistant. Such an optical cable 
OC11 can be manufactured, thus, in a particularly advantageous manner with 
high continuous speeds because through the robust construction of the 
optical bundle, the manufacturing process, for example the stranding 
process, can be maintained extensively without danger with regard to the 
mechanical stress. An impermissible stress of the optical waveguide in the 
interior of the optical bundle OB111 to OB114 is prevented by the 
particular protective effect of the especially constructed protective 
coverings SH111 to SH114. 
The outer jacket AM11 of the optical cable OC11 can be formed in 
multilayers. It is possible also to contain a metal band or foil ME11 as a 
diffusion block or as a ground steel strip as a protection from rodents. 
For the optical bundles OB5 to OB10, according to FIGS. 5-10, a wall 
thickness in the region of between 0.3 mm and 2.0 mm is advantageous. The 
inner diameter which serves to receive filling compound bundle FB 
containing the optical waveguide lies, in the exemplary embodiments 
according to FIGS. 5-10, approximately in the range of between 0.9 mm and 
4.0 min. In the exemplary embodiment according to FIG. 11, the diameter of 
the circle to be described in the optical bundles OB111 to OB114 is to be 
selected advantageously between 0.8 mm and 5.0 mm. 
The diameter of the tension-proof elements in FIGS. 5-11 lie approximately 
in the region of between 0.08 mm and 0.5 mm and the tension-proof elements 
advantageously fill only a proportion of 4% to 20% of the overall cross 
sectional area of the respective protective covering. 
The wall thickness of the protective coverings according to FIGS. 5-11 can 
be kept particularly low because, in contrast to the traditional 
approximately tubular and relatively rigid constructions, the mechanical 
tensile strength is obtained in the first instance by the embedded 
reinforcing elements. Therefore, such optical bundles are also easy to 
mold without an impermissible stress of the optical waveguide located in 
the interior, because this deformation in the first instance acts in the 
radial direction, while an impermissible stress in the axial direction is 
prevented through the embedded tension-proof elements. In respect to the 
exemplary embodiment according to FIG. 11, it should be noted that the 
optical bundles OB111 to OB114 represented there need not necessarily be 
manufactured with a sector-shaped cross section initially. Rather, it is 
also possible to manufacture these optical bundles, for example, in the 
circular form approximately analogous to the shape in FIGS. 6-11 and not 
impress the sector shape, or with the multi-layer arrangement a partial 
sector shape, onto the respective optical bundles until the processing 
procedure, for example during stranding. This subsequent shaping is 
possible if the wall thickness of the respective protective covering is 
selected to be particularly low, preferably between 5% and 20% of the 
diameter of the covering. 
The plastic material for the manufacture of the respective protective 
coverings can also consist of flame-resistant thermoplastics, or equipped 
with flame-resistant thermoplastics, wherein it is not necessary that the 
reinforcing elements for their part are equipped in a flame-resistant 
manner. Rather, these reinforcing elements can be made of a material which 
is not necessarily flame-resistant, since the reinforcing elements can be 
embedded and surrounded on all sides by the respective protective 
covering, wherein an orientation selection solely for tensile strength or 
possibly also the compressing properties can be paramount. The composite 
material of the protective covering, for example the respective optical 
bundle, is as a whole in any case flame-resistant and, to be more precise, 
independent of the characteristics of the respectively embedded 
reinforcing elements. 
The reinforcing elements are advantageously designed so that they act as 
tension-proof elements, as well as support elements, for example 
counteract an expansion of the protective covering as well as compression 
of the protective covering. Through the supporting effect, it is achieved 
that the shrinkage in the longitudinal direction is substantially 
determined only by the embedded reinforcing elements or their properties. 
A relatively small proportion of the reinforcing elements relative to the 
overall cross sectional face of the protective covering is already 
sufficient in order to produce this determining property of the 
reinforcing elements if the E-modulus of the reinforcing elements is 
selected to be correspondingly greater than that of the protective 
covering. Such properties are particularly desirable if a defined length 
relationship should be adjusted relative to the protective covering for 
the optical waveguide or waveguides contained loosely in the interior of 
the protective covering. For example, it is possible with a smaller cross 
sectional proportion of the reinforcing elements compared to the overall 
cross section of the protective covering to adjust in an accurate manner 
the fiber overlength at room temperature to .+-.0.01% by a targeted 
contraction. In this way within the scope of the invention, it is possible 
to tackle the problem of length, which always occurs when covering the 
optical waveguides, and to adjust in an accurate manner a possible desired 
overlength or an exact zero-overlength. The protective covering is cooled 
in the manufacturing process from the outside, for example by cooling 
water, and from the inside by the filling compound in which the optical 
waveguide or waveguides are embedded. 
In order to illustrate the relationship, reference is made to FIG. 12, 
which shows the cross section of a protective covering SH 12 in which 
reinforcing elements VE1 through VEn are embedded. The tubular protective 
covering SH12 is cooled from the outside, for example, by cooling water 
and from the inside by the filling compound FC as soon as the protective 
covering SH has left the extruder head and has been stretched onto the 
outer surface of the filling compound FC. The reinforcing elements VE1 
through VEn do not come directly into contact with either of the cooling 
agents, such as the cooling water from the outside or the filling compound 
FC from the inside. The reinforcing elements VE1 to VEn are rather cooled 
indirectly by the plastic layer SH12 of the tubular cross section 
surrounding them on all sides. 
A plastic material is used advantageously as a material for the protective 
covering SH12, which material, with regard to the E-modulus, is many times 
lower than the material for the reinforcing elements VE1 to VEn embedded 
in the tubular cross section. Advantageous E-modulus values of SH 11 lie 
between 50N/mm.sup.2 and 2000N/mm.sup.2, preferably in a range of 
300N/mm.sup.2 and 2000N/mm.sup.2. The material for the protective covering 
SH12 should moreover have the capacity, at room temperature, to break down 
gradually the stresses which were frozen, first of all, during cooling 
from the melting stage, i.e., the material should carry out a relaxation. 
The material for the reinforcing elements VE1 to VEn should, 
advantageously, have the following properties: 
Solidification temperature TV higher than solidification temperature TS of 
the protective covering SH12, for example TV=180.degree. C., 
TS=160.degree. C. 
E-modulus large, preferably 1500N/mm.sup.2 to 50000N/mm.sup.2, i.e., 
approximately 5 to 50 times the E-modulus of the protective covering SH12. 
The material should also have a linear temperature expansion coefficient, 
preferably .alpha..ltoreq.8.10.sup.-5 /K. 
If the construction according to the invention is compared with a known 
two-layer covering, in which, for example, the inner layer consists of 
polycarbonate and the outer layer consists of a polyethylene, then the 
following significant advantages will occur from the solution according to 
the present invention: 
a) The danger of the tension cracks, which is already reduced with the 
known construction through the tough-elastic outer polyethylene layer is 
again considerably reduced because the reinforcing elements VE1 to VEn do 
not come into direct contact with the constantly cooler filling compound 
FC after the extrusion process, but are rather gradually cooled indirectly 
by way of the material of the protective covering SH12; 
b) With the known two-layer covering with a high tensile inner layer, there 
is the danger that tension cracks, which can occur at a point, for example 
through a material defect or an irregularity in the manufacturing process, 
will continue there and possibly extend to the overall cross section, for 
example around the periphery. With the invention, this is not the case, 
because, for example, a point of disturbance in the reinforcing element 
VE1 remains restricted to this element and does not cross over to adjacent 
reinforcing elements, for example the element VEn. In the worst case, 
therefore, with such a disorder in the material or in the manufacturing 
process, the result can be damage of an individual reinforcing element, 
not, however, of all of the reinforcing elements VE1 through VEn extending 
over the periphery of the jacket. 
c) The reinforcing elements VE1 to VEn have no direct contact with the 
filling compound FC and it is, therefore, not necessary that notice is 
taken whether the material of the elements VE1 to VEn is also sufficiently 
resistant to this filling compound FC, for example, with regard to the 
solvents used in the filling compound, moisture, etc. Because the 
reinforcing elements VE1 to VEn are embedded on all sides in the material 
of the protective covering SH6, it is insured that no interaction can 
occur between the filling compound FC, on the one hand, and the 
reinforcing elements VE1 to VEn, on the other hand. 
d) The covering construction, for example according to FIG. 12, results in 
a more compact arrangement without a continuous interface, such as occurs 
with known concentric multi-layer coverings. Through the embedding of the 
thin reinforcing elements VE1 to VEn with a relatively small cross section 
into the protective covering SH6, which, in contrast, is much greater in 
terms of volume, there is a substantially homogeneous shape, an improved 
embedding, a tighter mechanical bond and altogether a more favorable 
property. Materials can, therefore, be used for the reinforcing elements 
VE1 to VEn which also tend more to tension cracks, for example 
polycarbonate polyamide 6 or polyetherimide, because the problem of the 
sensitivity to tension cracks is reduced to a great extent with the design 
according to the present invention. 
Some influences triggering tension cracks, such as states of high stress 
through various cooling behavior of the polymers and the influence of the 
wetting agents, that means agents which encourage tension cracks, are 
reduced because each supporting element VE1 to VEn is completely 
surrounded by the material of the protective covering SH6. 
Advantageously in this context, the material of the protective covering 
SH12 can be extruded at a temperature which lies above the melting or 
fusing temperature of the reinforcing elements VE1 to VEn. The 
solidification of the reinforcing elements VE1 to VEn occurs with an 
indirect cooling via the covering material, wherein the actual cooling 
agents necessary for the cooling process, for example cooling water on the 
outside and the filling compound on the inside, does not come into direct 
contact with the embedded reinforcing elements VE1 to VEn. For these 
considerations, it can be advantageous, when the embedding location of the 
supporting elements are seen in the radial direction, to select the 
embedding location in a particularly advantageous manner on the basis of 
the following considerations. 
In FIG. 12, the temperature gradient (temperature curve) TGA, which is 
produced through the quantity and the temperature of the outside cooling 
medium and dependent on the time for the cross section of the protective 
covering SH12 is represented for a fixed radial cross section, for example 
with the reinforcing element VE1. This temperature gradient TGA is steeper 
with the greater cooling that takes place from the outside, and flatter 
when less cooling takes place. This temperature gradient is, therefore, 
able to be freely selected, dependent on the desired conditions, because 
the outer cooling is a parameter which can be adjusted for the 
manufacturing process. In contrast, an inner temperature gradient TGI, 
which occurs for the inner wall of the protective covering SH12, is 
dependent only on the starting temperature of the filling compound FC and 
results substantially from the properties of the filling compound FC 
already present, and it is hardly able to change by any amount. Both 
temperature gradients TGI, which is dependent on the filling compound FC, 
and TGA, which is dependent on the outer cooling, for example water, 
intersect at a certain point which lies somewhere between the inner face 
and the outer face of the protective covering SH12. The associated radius 
is denoted by R1 and it is advantageous to arrange reinforcing elements 
VE1 just like the remaining reinforcing elements, approximately where the 
temperature gradients TGA and TGI intersect and to select the point of 
intersection SPT of both curves relative to the temperature T so that the 
solidification temperature RV of the reinforcing elements VE1 to VEn lies 
just there. The result of this is that with the respective reinforcing 
elements, for example VE1, approximately the same temperature is present 
at the inside and outside of the element. To illustrate these 
relationships, reference is made to FIG. 13, wherein an enlarged partial 
cut-away section of the protective casing SH12 is presented. The 
temperature TA present outside of the reinforcing element VE1 is 
substantially conditioned by the outer temperature curve TGA, while on the 
inside of the reinforcing element VE1, the temperature TI is present and 
is substantially obtained by the flatter inner temperature gradient curve 
TGI. The aim is that at the time of solidification, or the glass 
transition temperature of the reinforcing element VE1, the temperature TI 
is approximately the same as the temperature TA so that no tension due to 
the temperature occurs at the reinforcing element VE1, which would result 
in the reinforcing element VE1 attempting to bend. Thus, a tension freeze 
during the cooling process does not occur. At the time of the 
solidification of the reinforcing elements VE1 to VEn, approximately 
TV=TA=TI should be applicable. The freezing of tensions would also involve 
the danger of formation of cracks. If, on the other hand, the temperatures 
TA and TI are selected to be approximately the same at the moment of the 
solidification of the reinforcing elements VE1 to VEn, then no such state 
of tension condition occurs from the outset during the cooling process. 
Thus, for a predetermined inner temperature gradient curve TGI and an outer 
temperature gradient curve, TGA, a position of the reinforcing elements 
can be selected so that the solidification temperature IV will come to lie 
approximately at the point of intersection of both curves TGI and TGA. 
Therefore, this point will be at a distance of R1 from the center point of 
the tubular composite protective covering SH12 of FIG. 12. 
It is, however, also possible to alter the parameters which influence the 
temperature curves TGI and TGA, for example the temperature of the cooling 
water and the throughflow speed thereof, and the length of the cooling 
distance, so that the curves TGI and TGA intersect at such a point where 
the respective reinforcing elements VE1 to VEn are arranged in an optimum 
manner, for reasons of stability inside the protective covering SH. 
The result is, again, for example, according to FIG. 13 inside the 
reinforcing element VE1, after the point in time or point of intersection 
SPT in FIG. 12, so that a temperature gradient between the temperature TA 
and TI and, namely in each case, a radial direction from the outside 
toward the inside. This temperature gradient is, however, no longer of 
particular importance, because in the meantime, the solidification of the 
reinforcing elements VE1 to VEn has occurred and the tensions are no 
longer frozen. 
Through the embedding of the reinforcing elements VE1 to VEn in the 
covering material and the enveloping thereof on all sides by this covering 
material, chemical influence-encouraging tension cracks through 
components, for example, the filling compound or of the coating of the 
optical waveguides LW1 to LWn, as well as mechanical effects, encouraging 
tension cracks through the cooling behavior can be reduced or completely 
removed. 
In terms of technology of the method, individual elements VE1 through VEn 
embedded into the material of the protective covering SH12 are also 
advantageous because of the important tool parts for an optimum shaping 
out of the fusion. For example, the respective spike or the nozzle only 
comes into contact with the material of the corrective covering SH6. In 
contrast to a two-layer covering of a known construction, the wall 
adhesion in the tool for forming out to the tube interior or outer side is 
almost the same. Neither can the results be deposited, the results of 
which would be flow interference. This danger exists with long-running 
times with the melting of these hard polymers. Because of this fact, it is 
guaranteed that various flow characteristics of the individual material 
combinations which can lead to the shear stress, even in the melted cone 
during the forming-out, do not occur. 
Subsequently, three exemplary embodiments for the manufacture of the 
optical waveguide-core-protective are given: 
EXAMPLE 1 
Outer diameter of SH12: 2.8 mm; 
Inner diameter of SH12: 1.7 mm; 
Material of the protective covering SH12: polypropylene; 
Material of the reinforcing elements VE1 to VEn: polycarbonate; 
Number n of the reinforcing elements: 36; 
Diameter 2(R1) of the partial circle on which VE1 to VEn are arranged: 2.0 
mm; 
Diameter of the reinforcing elements VE1 to VEn: 0.1 mm; 
Filling compound FC: thixotropic hydrocarbon-filling compound; 
Extrusion temperature TXS of the protective covering SH12: 230.degree. C.; 
Extrusion temperature TXV of the reinforcing elements VE1 to VEn: 
270.degree. C.; 
Manufacturing speed: 200 m/min; and 
Adjusted fiber length 0 to 0.1%. 
EXAMPLE 2 
Outer diameter of protective covering SH12: 6.0 mm; 
Inner diameter of the protective covering SH12: 3.6 mm; 
Material of the protective covering SH12: linear polyethylene; 
Material of the reinforcing elements VE1 to VEn: polycarbonate; 
Number n of the round reinforcing elements VE1 to VEn: 36; 
Diameter of the reinforcing elements VE1 to VEn: 0.2 mm; 
Diameter 2 (R1) for the partial circle of the reinforcing elements 4.4 mm; 
Extrusion temperature TXS of the protective covering SH12: 225.degree. C.; 
Extrusion temperature TXV of the reinforcing elements VE1 to VEn: 
270.degree. C.; 
Manufacturing speed: 40 m/min; 
Fiber overlength: 6%; and 
Cooling at intervals water/air and hot air distance. 
EXAMPLE 3 
Outer diameter of the protective covering SH12: 3.5 mm; 
Inner diameter of the protective covering SH12: 2.1 mm; 
Material of the protective covering SHG: polybutylene terephthalate; 
Material of the reinforcing elements VE1 to VEn: polyamide 12; 
Number n of the round reinforcing elements VE1 to VEn: 36; 
Diameter of reinforcing elements VE1 to VEn: 0.15 mm; 
Diameter 2(R1) for the partial circle of the reinforcing elements: 2.5 mm; 
Extrusion temperature TXS of the protective covering SH12: 260.degree. C.; 
Extrusion temperature TXV of the reinforcing elements VE1 to VEn: 
260.degree. C.; 
Manufacturing speed: 120 m/min; 
Fiber overlength: 0.025%; and 
Cooling with cold water. 
The extrusion temperature TXS of the protective covering SH12 is 
advantageously selected at or below the extrusion temperature TXV of the 
reinforcing elements VE1 to VEn. 
Although various minor modifications may be suggested by those versed in 
the art, it should be understood that we wish to embody within the scope 
of the patent granted hereon all such modifications as reasonably and 
properly come within the scope of our contribution to the art.