Abstract:
An optical cable has optical transmission elements stranded about a central reinforcing member. The optical transmission elements are alternatively stranded in a first and second direction of rotation. A sheath surrounds the optical transmission elements, and markings are applied to the sheath to indicate switchback locations in the cable. The markings are applied to the sheath, which is separate from the optical transmission elements. Therefore, the markings need not be applied directly to the transmission elements, so the same control signal can be used to switch the direction of stranding and to apply the marking.

Description:
PRIORITY APPLICATION 
       [0001]    This application claims the benefit of German Application No. 202009006357.7 filed on Apr. 30, 2009, the entire contents of which are herein incorporated by reference. 
       SUMMARY 
       [0002]    In one embodiment, an optical cable comprises optical transmission elements which are intended for the transmission of light over relatively great distances. Each of the optical transmission elements may contain a number of optical waveguides, which are surrounded by a buffer tube. A number of these optical transmission elements may be arranged in a stranded manner in the cable core of the optical cable. 
         [0003]    The stranded arrangement of the optical transmission elements gives the optical cable great flexibility. In the case of SZ stranding, the optical transmission elements are stranded in the longitudinal direction of the cable core initially with a number of revolutions in one direction of rotation and subsequently stranded in the longitudinal direction of the cable with a number of revolutions in the opposite direction. Consequently, the optical transmission elements are arranged alternately in an S stranded form and a Z stranded form on adjacent portions of the cable core. To fix the stranding, the optical transmission elements are held together by a holding helix. 
         [0004]    As a result of the stranding, the optical transmission elements have an excess length with respect to the length of the cable. The excess length is used to splice the optical waveguides of the optical transmission elements with further optical waveguides, in particular at a reversal position, at which the stranding direction changes from the S stranded form to the Z stranded form. For this purpose, the holding helix is removed at a reversal position. 
         [0005]    It is often necessary to provide an already laid optical cable with branching nodes, at which the optical waveguides of the optical cable branch in different directions. For protection, the cable core of an optical cable may be surrounded by an outer cable jacket, with the result that the reversal points cannot be directly located by viewing the cable from the outside. If branching of the optical transmission elements by splicing optical waveguides of the optical cable with further optical waveguides is retroactively performed in the case of an optical cable with a cable jacket, the cable jacket must be removed at a reversal position of the stranding direction of the optical transmission elements. If, for example, the optical cable has reversal positions at intervals of 50 cm, in the worst case the cable jacket has to be removed over the entire 50 cm portion of the cable in order to find the reversal position. 
         [0006]    In a region around the reversal position, the holding helix that holds the optical transmission elements together is removed. On account of the excess length, the optical waveguides contained in the buffer tubes of the optical transmission elements can be easily placed into a splicing device and spliced with further optical waveguides. 
         [0007]    It is desirable to specify an optical cable in which a reversal position at which the stranding direction changes can be easily established. Furthermore, it is desirable to specify an arrangement for producing an optical cable in which a reversal position at which the stranding direction of the optical transmission elements changes can be easily established. 
         [0008]    An embodiment of an optical cable comprises a number of stranded optical transmission elements which contain at least one optical waveguide. The optical transmission elements are arranged in a stranded manner such that the optical transmission elements are stranded in a first direction of rotation on a first portion of the cable and are stranded in a second direction of rotation, which is different from the first direction of rotation, on a second portion of the cable, arranged adjacent to the first portion. The cable also has a sheath, surrounding the optical transmission elements, with a marking arranged on a surface of the sheath to identify a position between the first portion and the second portion of the cable. The marking is designed in such a way that the marking is distinguishable from a region of the sheath surrounding the marking. 
         [0009]    According to a further embodiment, the sheath surrounds the optical transmission elements in such a way that the marking on the surface of the sheath is arranged between the first portion and the second portion of the cable. According to a further embodiment, the optical transmission elements are arranged in a stranded manner such that a change between the first direction of rotation and the second direction of rotation takes place at a position between the first portion and the second portion of the cable. To identify the position on the surface of the sheath, the marking is arranged at the position of the sheath at which the sheath surrounds the position. 
         [0010]    According to a further embodiment, the marking is designed in such a way that the position identified by the marking on the surface of the sheath is detectable. According to a further embodiment, the material of the marking is distinguishable from a material of a region of the sheath surrounding the marking. 
         [0011]    The marking may be arranged on a side of the surface of the sheath that is facing the optical transmission elements. The marking may be arranged circumferentially around the optical transmission elements on the side of the surface of the sheath that is facing the optical transmission elements. According to a further embodiment of the optical cable, the marking may be formed as a component which is arranged on the surface of the sheath by an adhesive connection. The marking may be formed as a metal strip. The marking may, for example, contain aluminium or a magnetic material. According to a further embodiment, the marking may be formed as a transponder. 
         [0012]    The sheath may contain a dielectric material or a material composed of polyester or a material composed of paper. The sheath may, for example, contain a material which brings about an increase in volume of the sheath on contact with water. According to a further embodiment of the optical cable, the sheath may be surrounded by a filament or yarn. Furthermore, the sheath may be surrounded by a cable jacket. The marking is designed in such a way that the position identified by the marking is detectable through the cable jacket. 
         [0013]    According to a further embodiment of the optical cable, the optical transmission elements may be surrounded by a holding element. The optical transmission elements may be arranged in a stranded manner around a central element. The optical transmission elements may, for example, be arranged in an SZ stranding pattern. According to a further embodiment of the optical cable, an armouring of a metallic material is arranged between the sheath and the cable jacket. It is also possible, for example, for yarns of aramid or glass to be arranged between the sheath and the cable jacket. 
         [0014]    An arrangement for producing an optical cable according to one of the embodiments given above is specified below. The arrangement comprises a stranding device for stranding the optical transmission elements of the optical cable. The stranding device is formed in such a way that the optical transmission elements are arranged such that they are stranded in a first direction of rotation on a first portion of the optical cable and are stranded in a second direction of rotation, which is different from the first direction of rotation, on a second portion of the optical cable, which is arranged adjacent to the first portion. A switching over of the stranding device between the first direction of rotation and the second direction of rotation is controlled by a control signal. The arrangement has, furthermore, an identification device for applying a marking to a strip to identify a position between the first portion and the second portion of the cable. The application of the marking is controlled by the control signal. Furthermore, the arrangement comprises a sheath forming device for forming the strip into a sheath around the optical transmission elements of the optical cable in such a way that the marking is arranged between the first portion and the second portion of the cable. 
         [0015]    According to a further embodiment of the arrangement, the stranding device and the identification device are respectively arranged at a distance from the sheath forming device, so that the marking is arranged between the first portion and the second portion of the optical cable after the sheath has been formed around the cable core. Furthermore, a transporting speed with which the optical transmission elements are fed to the sheath forming device from the stranding device, and a transporting speed with which the strip is fed to the sheath forming device from the identification device are chosen in such a way that the marking on the surface of the sheath is arranged between the first portion and the second portion of the cable. In the case of a further embodiment of the arrangement, the optical transmission elements are stranded by the stranding device in such a way that a change between the first direction of rotation and the second direction of rotation takes place at a position between the first portion and the second portion of the cable. The marking is arranged by the identification device on the surface of the strip at a position at which the strip formed into a sheath surrounds the position. For example, the marking is arranged on the strip at an interval which corresponds to the length of one of the first and second portions of the cable. The marking may, for example, be adhesively attached on the strip when the identification device is activated by the control signal. A material which contains a metal may be arranged on the strip by the identification device. Furthermore, a transponder may be arranged on the strip by the identification device. 
         [0016]    The sheath forming device may be formed in such a way that, after the sheath has been formed around the optical transmission elements, the marking is arranged on a surface of the sheath that is facing the optical transmission elements. Furthermore, the arrangement comprises an extruding device for surrounding the sheath with a cable jacket. According to a further embodiment, the arrangement may comprise a detecting unit for detecting the marking, an armouring winding device for arranging the armouring over the sheath and a printing device for applying an identification to the cable jacket of the optical cable. The detecting unit is arranged between the sheath forming device and the armouring winding device and the armouring winding device is arranged between the detecting unit and the printing unit. The printing unit arranges the identification on the cable jacket when the detecting unit detects the marking. 
         [0017]    A method for producing an optical cable is specified below. According to the method, a number of optical transmission elements which contain at least one optical waveguide are provided. The optical transmission elements are stranded along a first portion of the optical cable in a first direction of rotation and are stranded along a second portion of the optical cable, arranged adjacent to the first portion, in a second direction of rotation, which is different from the first direction of rotation, wherein switching over between the stranding in the first direction of rotation and the second direction of rotation takes place by activating a stranding device with a control signal. A marking is applied to the surface of the strip by activating an identification device for arranging the marking with the control signal. The marking is designed in such a way that the marking is distinguishable from a region of the strip surrounding the marking. The strip is formed into a sheath. The optical transmission elements are surrounded by the sheath in such a way that the marking is arranged between the first portion and the second portion of the optical cable. 
         [0018]    According to a further embodiment, the marking is arranged on the strip when the stranding device is activated with the control signal. The marking may, for example, be arranged on the strip by adhesively attaching a material that is different from the material of the strip onto the strip. For example, a material which contains a metal may be arranged on the strip. For example, a transponder may be arranged as the marking on the strip. 
         [0019]    According to a further embodiment of the production method, the optical transmission elements are surrounded by the sheath in such a way that the marking is arranged on a surface of the sheath that is facing the optical transmission elements. 
         [0020]    According to a further embodiment of the production method, the sheath is surrounded by a cable jacket. In the case of a further embodiment of the production method, it is provided that first the detection of the marking is carried out, then the surrounding of the sheath with an armouring and subsequently the application of a marking to the cable jacket, when the marking has been detected. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    Embodiments of an optical cable and an arrangement for producing the optical cable are explained on the basis of the following figures. Furthermore, a method for producing such an optical cable is specified on the basis of the figures, in which: 
           [0022]      FIG. 1  shows an embodiment of an arrangement for producing a cable core of an optical cable, 
           [0023]      FIG. 2  shows an embodiment of a jacketing line for producing an optical cable with a cable core surrounded by a cable jacket, 
           [0024]      FIG. 3  shows a further embodiment of a jacketing line for producing an optical cable with a cable core surrounded by a cable jacket, 
           [0025]      FIG. 4  shows an embodiment of an optical transmission element, 
           [0026]      FIG. 5  shows an embodiment of a cable core with stranded optical transmission elements, 
           [0027]      FIG. 6  shows optical transmission elements after removal of a holding helix at a reversal position, 
           [0028]      FIG. 7  shows an embodiment of a strip for applying a sheath around a cable core of the optical cable, 
           [0029]      FIG. 8  shows an embodiment of an optical cable with a marking to identify a reversal position of the stranding direction of optical transmission elements. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  shows an embodiment of an arrangement  1  for producing a cable core  100  of an optical cable. The cable core comprises optical transmission elements  10 , which are arranged in a stranded manner in the longitudinal direction of the cable. To produce the cable, first a reinforcing element  20  is provided. The reinforcing element  20  comprises, for example, a material composed of a glass fibre reinforced plastic. The reinforcing element  20  serves for strengthening the cable structure and may, for example, be provided as a central element in the cable core. The optical transmission elements may be arranged in a stranded manner around the reinforcing element  20 . 
         [0031]    The optical transmission elements  10  are provided for stranding by being arranged on storage devices  1100 . In the case of the arrangement shown in  FIG. 1 , the storage devices are formed as drums on which the optical transmission elements are wound up.  FIG. 4  shows a possible embodiment of an optical transmission element  10 . The optical transmission element  10  comprises a buffer tube  12 , which contains one or more optical waveguides  11 . The optical waveguides  11  comprise a light-guiding core, which is surrounded by a coating. In the case of the arrangement shown in  FIG. 1 , for example, an optical transmission element is selectively wound up on each of the drums  1100 . The optical transmission elements are distinguishable from the coating  12 , for example in colour. The optical transmission elements are guided from the drums  1100  to a stranding device  1000 . 
         [0032]    The stranding device  1000  may, for example, comprise an annular disc  1200 . By means of a hole in the interior of the annular disc, the outer ring of the disc may be arranged around the reinforcing element  20 . The reinforcing element  20  is led through the hollow of the annular disc. The outer ring  1200  of the disc contains openings for guiding the optical transmission elements  10 . Each of the optical transmission elements is led through one of the openings. 
         [0033]    During rotation of the stranding device  1000 , the optical transmission elements  10  are arranged in a stranded manner around the reinforcing element  20  when the reinforcing element is moved through the annular disc in the direction of the arrow. To control the rotation of the annular disc, the stranding device is activated by a control signal S. In dependence on the control signal S, the direction of rotation of the disc  1200  changes. With the stranding device shown in  FIG. 1 , the optical transmission elements  10  can, for example, be arranged around the reinforcing element  20  in an SZ stranding pattern. 
         [0034]    To create the SZ stranding pattern, the stranding device rotates for a number of revolutions, for example for three revolutions, in one direction, until the direction of rotation is changed by activation of the stranding device with the control signal S. After activation of the stranding device  1000  with the control signal S, the annular disc  1200  of the stranding device rotates for several revolutions in the opposite direction, until the direction of rotation is once again changed by activation of the stranding device with the control signal S. Consequently, reversal positions at which the stranding direction of the optical transmission elements on the cable core changes are produced at certain intervals, for example at intervals of between 0.4 and 0.6 m. In the case of the embodiment of the production line for producing the cable core that is shown in  FIG. 1 , the optical transmission elements  10  are arranged such that they are stranded in a direction of rotation to the right on the portions B 1  of the cable and stranded in a direction of rotation to the left on the portions B 2  of the cable, arranged adjacent thereto. At the reversal positions identified by RP, the stranding direction respectively changes. 
         [0035]    To fix the stranding, the holding-helix winding device  4000  is provided. By means of the holding-helix winding device  4000 , a holding helix  400 , for example a filament or a yarn, is wound around the stranded optical transmission elements. In the case of the arrangement for producing the optical cable that is shown in  FIG. 1 , at least two yarns are arranged around the optical transmission elements in a cross-wound fashion. The cross holding helix  400  serves for fixing the stranding of the optical transmission elements  10  around the reinforcing element  20 . 
         [0036]      FIG. 5  shows adjacently arranged portions B 1 , B 2  of the cable after application of the cross holding helix  400 . A number of optical transmission elements  10  are arranged in the SZ stranding pattern. Along the portion B 1  of the cable, the optical transmission elements are arranged such that they are stranded in a direction of rotation U 1  to the left in the longitudinal direction around a reinforcing element  20  that is not shown in  FIG. 5 . At the position RP, the direction of rotation changes, so that the optical transmission elements  10  in the region B 2 , which is adjacent to the region B 1 , are arranged such that they are stranded in a direction of rotation U 2  to the right around the reinforcing element. The cross holding helix  400  serves for fixing the SZ stranding pattern. 
         [0037]      FIG. 6  shows the optical transmission elements  10  after removal of the holding helix  400  at the reversal position RP. On account of the excess length, a sagging of the optical transmission elements  10  occurs after removal of the cross holding helix. The excess length may be used for the purpose of removing the optical waveguides from the optical transmission elements and splicing them with further optical waveguides. In particular, the excess length makes it possible for the optical waveguides to be easily placed in a splicing device for splicing with further optical waveguides. 
         [0038]    The cable core  100  may be further processed without any filler or be surrounded by a filling composition  100  in the production arrangement. The filling composition serves for protecting the optical transmission elements  10  from mechanical damage and can additionally prevent the ingress of water into the cable core. In order for the optical transmission elements  10  to be surrounded by the filling composition  500 , a filling device  5000  is provided downstream of the holding-helix winding device  4000 . The optical transmission elements are surrounded by the filling composition  500  by the filling device  5000 . Polyolefin-based greases may be used, for example, as the filling composition. 
         [0039]    The cable core  100  is surrounded by a sheath  200 . The sheath  200  is first provided on a storage device  2100  in the form of a narrow strip. The storage device  2100  may be a drum, on which the sheath  200  is wound up to form an elongated strip. The sheath  200  may, for example, contain a dielectric material. It may, for example, also comprise a material composed of a plastic, for example of polyester, or composed of paper. The sheath  200  may be provided as a thin film of plastic with a smooth surface or as a nonwoven with a porous surface on the storage drum  2100 . 
         [0040]    In a sheath forming device  2000 , the strip is formed into a sheath and arranged circumferentially around the cable core  100 . The strip  200  may, for example, have a width which corresponds to the circumference of the cable core. The strip may also be slightly wider than the circumference of the cable core, for example wider by 2 mm to 4 mm than the circumference of the cable core. If the strip is wider than the circumference of the cable core, after it has been formed into a sheath the strip surrounds the cable core completely, or the edges of the strip overlap by the width of the strip that goes beyond the circumference of the cable core. If the strip has a width which is greater than the circumference of the cable core, it is ensured that, in the event of shrinkage of the strip as a result of tensile loading or as a result of a temperature change, the cable core is nevertheless completely surrounded by the sheath  200 . 
         [0041]    After the nonwoven or the film has been formed into a sheath, the sheath serves for protecting the cable core from high temperatures, which occur for example during an extrusion operation when extruding a cable jacket. The strip  200  may be coated on one or both sides with a SAP (Super Absorbent Polymer) powder. If the SAP powder comes into contact with moisture, the material swells and consequently brings about an increase in volume of the sheath. As a result, the cable core is protected from the ingress of water. 
         [0042]    Provided between the strip runout of the strip  200  from the drum  2100  and the sheath forming device  2000  is an identification device  3000 . In the case of the embodiment shown in  FIG. 1 , the identification device  3000  is coupled to a storage drum  3100 . Arranged as markings on the drum  2100  are, for example, labels on a backing material  320  in strip form. The labels may, for example, be strips of a metal which comprise a layer of adhesive  310  on their underside. The labels may be applied to the backing strip by means of the layer of adhesive. According to a possible embodiment, the labels may, for example, be thin metal platelets of aluminium or some other metal. The metal platelets may have a height of between 30 μm and 70 μm. The markings may, for example, be rectangular and have a width of between 5 mm and 20 mm and a length of between 30 mm and 50 mm. 
         [0043]    The markings  300  are arranged on the strip  200  by the identification device  3000 . The application of the markings takes place by activation of the identification device  3000  with the control signal S, which is also already used for switching over the direction of rotation of the stranding device. When the identification device  3000  is activated with the control signal S, one of the markings, for example one of the aluminium labels, which at first is still applied to the backing strip  320 , is pulled off from the backing strip  320  and arranged on the strip  200 . For the layer of adhesive  310  of the label  300  to be detached as far as possible without leaving any residue, the backing strip  320  may be coated with Teflon. 
         [0044]    Since the same control signal S that also serves as a switching-over signal for changing the direction of rotation of the stranding device is used for controlling the points in time at which the labels are arranged on the strip  200 , the application of a marking to the strip  200  takes place synchronously with the changing of the direction of rotation of the annular disc  1200  of the stranding device  1000 . Consequently, the markings  300  are arranged on the strip at an interval VL which corresponds to the length of the portion of the cable on which the optical transmission elements are arranged such that they are stranded in one specific direction of rotation. 
         [0045]    From the identification device, the strip  200  provided with the markings runs over a compensating element  2200  and a guiding wheel  2300  to the sheath forming device  2000 . The compensating element  2200  has various rollers, over which the strip  200  is led. In the case of the arrangement show in  FIG. 1 , the compensating element altogether comprises three rollers, the middle roller being movably arranged. The compensating element makes it possible to compensate for tensile forces on the strip  200 , which occur when the strip is unwound from the storage drum  2100  and when the strip is formed into the sheath  200 . 
         [0046]    In the case of the embodiment of the cable shown in  FIG. 1 , the cable core  100  is surrounded by the strip  200  in such a way that the markings  300  arranged on the surface of the strip are arranged over the reversal positions RP, at which the stranding direction of the optical transmission elements changes.  FIG. 7  shows the strip  200  after the adhesive attachment of the markings  300  by the identification device  3000 . The markings  300  are formed, for example, as thin metal platelets, the length of which is slightly less than the width of the strip. This ensures that the cable core is circumferentially surrounded by the markings  300  virtually completely at the reversal positions when the strip is formed into a sheath. The synchronous activation of the stranding device  1000  and the identification device  3000  with the same control signal S has the effect that markings  300  are arranged on a surface  201  of the strip at positions SH of the strip with the interval VL, which corresponds to the interval between the reversal positions RP of the cable core. Between the markings, the optical transmission elements  10  are stranded in different directions of rotation around the cable core under the portions H 1  and H 2  of the sheath  200 . 
         [0047]    In the sheath forming device  2000 , the strip is formed into a sheath in such a way that the markings are arranged on a surface  201  on the inner side of the sheath that is facing the cable core  100  and the optical transmission elements  10 . The markings are consequently not visible on the outwardly facing surface of the sheath. Since the markings are arranged on the surface  201  of the sheath  200  that is facing the optical transmission elements  10 , the markings are protected from becoming detached from the material of the sheath  200  by subsequent method steps, such as for example the extrusion of a cable jacket around the sheath  200 . 
         [0048]    In order to ensure that the markings  300  are actually arranged over the reversal positions RP after the strip is formed into the sheath  200  around the cable core, the length between the identification device  3000  and the sheath forming device  200  may be adapted to the length between the stranding device  1000  and the sheath forming device  2000 . According to a possible embodiment, the length of the distance which the strip  200  passes over between the identification device  3000  and the sheath forming device  2000  corresponds to the length of the distance which the cable core covers between the stranding device  1000  and the sheath forming device  2000 . If the cable core  100  with the stranded optical transmission elements  10  and the strip  200  are moved at the same speed, the markings  300  are arranged over the reversal positions RP after the strip has been formed into a sheath and after the sheath has been applied over the cable core. 
         [0049]    In the case of the embodiment of the production arrangement  1  shown in  FIG. 1 , the length of the distance which the strip  200  covers between the identification device  3000  and the sheath forming device  2000  may be different from the length of the distance which the cable core  100  passes over between the stranding device  1000  and the sheath forming device  2000 . If the length of the distance which the strand  200  covers from the identification device  3000  to the sheath forming device  2000  is, for example, less than the distance which the cable core passes over between the stranding device  1000  and the sheath forming device  2000 , the identification device  3000  may indeed be likewise activated by the control signal S to apply the marking  300  to the strip  200 , but the application of the marking  300  to the strip  200  may take place with a time delay. 
         [0050]    Even if the length of the distance which the strip  200  covers from the identification device  3000  to the sheath forming device  2000  is longer than the distance which the cable core passes over between the stranding device  1000  and the sheath forming device  2000 , the identification device  3000  may be controlled by the control signal S to apply the marking  300  to the strip  200 . As a result, the marking  300  is arranged on the strip  200  synchronously with the switching over of the direction of rotation of the stranding device  1000 . In order to ensure that the reversal position RP on the cable core and the marking  300  on the strip  200  arrive at the sheath forming device at the same time, the transporting speed of the strip  200  may be increased. 
         [0051]    By setting the time delay with which the markings are arranged on the strip  200 , the transporting speed with which the strip  200  and the cable core  100  are moved, or by matching the length of the distance between the stranding device and the sheath forming device on the one hand and the length of the distance between the identification device and the sheath forming device on the other hand, the markings can be arranged over the reversal positions RP on the strip  200  with an accuracy of +/−20 mm. 
         [0052]    For fixing the strip  200  that has been formed into a sheath and surrounds the cable core, a holding-helix winding device  6000  is provided. By means of the holding-helix winding device  6000 , a holding helix  600 , for example a filament yarn, is wound around the sheath  200 . The holding helix prevents the backing strip  200  that has been formed into a sheath from coming apart under restoring forces. After the holding helix  600  has been applied to fix the sheath  200 , the cable core is wound up on a storage drum  6100 . 
         [0053]      FIG. 2  shows an arrangement  2  for producing an optical cable, with which the sheath  200  is surrounded by a cable jacket. The arrangement comprises an extruding device  7000  for extruding the cable jacket around the sheath  200 . In the extruding device, a material of the cable jacket, for example a material composed of polyethylene, is heated and extruded around the sheath  200 . 
         [0054]      FIG. 8  shows an embodiment of an optical cable  4 , which can be produced with the arrangements for producing optical cable that are shown in  FIGS. 1 and 2 . The optical cable has inside the cable core  100  a reinforcing element  20 , for example a glass fibre reinforced element, around which the optical transmission elements  10  are arranged in an SZ stranding pattern. Each of the optical transmission elements contains inside it one or more optical waveguides  11 , which are surrounded by a thin buffer tube  12 . The cable core may be filler-free or contain a filling composition  500 , in which the optical transmission elements  10  are embedded. The cable core  100  is surrounded by the sheath  200 . The sheath  200  may contain a material composed of a plastic, for example a material composed of polyester. 
         [0055]      FIG. 8  shows the cross section through an optical cable  4  at a reversal position RP, at which the stranding direction of the optical transmission elements  10  changes from one direction of rotation to an opposite direction of rotation. For example, at the cross-sectional position shown in  FIG. 8 , the stranding changes from an S stranding direction to a Z stranding direction. To identify the reversal position, the marking  300  is applied to the surface  201  of the sheath  200  that is facing the cable core  100  or the optical transmission elements  10 . The marking  300  may, for example, be a thin metal platelet, for example an aluminium label, with a layer thickness of between 30 μm and 70 μm, which is adhesively attached on the inner surface of the sheath  200 . The marking may have a length such that the standard optical transmission elements  10  are circumferentially surrounded by the marking. Around the sheath  200 , consequently also around the marking  300 , the cable jacket  700  is extruded with a ripcord  710  for easy removal of the cable jacket. The small layer thickness of the labels makes it possible for no thickenings to occur along the optical cable in the region of the reversal positions and make the marking bend in the cylindrical form of the sheath. 
         [0056]    If they take the form of thin metal platelets that are adhesively attached on the inner side  201  of the sheath  200 , for example, the markings may be detected by a metal detector through the cable jacket. If the optical cable is already laid in the ground and/or in a non-metallic pipe, is consequently no longer required to remove the cable jacket over a relatively long portion, corresponding to the interval VL between two reversal positions, in order to find a reversal position. Since the markings are placed on the strip  200  synchronously with the switching over of the direction of rotation of the stranding device and, given suitable adaptation of the distances between the stranding device and the sheath forming device on the one hand and between the identification device and the sheath forming device on the other hand, are arranged on the sheath  200  over the reversal positions, each reversal position can be determined by detecting the marking arranged over it on the underside  201  of the sheath through the cable jacket by means of a reader. Consequently, the cable jacket can be removed specifically at the determined position for the splicing of the optical waveguides. A cable sleeve, which is fitted over the opened location after splicing to protect the interior of the cable, can therefore have small dimensions. Since the marking  300  surrounds the cable core over the entire circumference, the reversal position can be detected by the reader from all sides. 
         [0057]    As an alternative to markings in the form of aluminium metal platelets, magnetic labels may also be used. The magnetic labels are coated on the underside with a layer of adhesive and are adhesively attached onto the strip  200  under control of the identification device  3000  or of the stranding device when the identification device is activated by the control signal S, which is also used for controlling the switching over of the direction of rotation of the stranding device. In the case of an optical cable in which the cable core is protected by a cable jacket, labels with magnetic properties can likewise be determined by a reader, for example a negative field detector, through the cable jacket. 
         [0058]    A further possibility for identifying a reversal position of the stranding direction is to apply radio transponders, for example RFID transponders, to the strip by means of the identification device  3000 . The position of the RFID transponders on the underside of the sheath  200  can likewise be detected through the cable jacket by a reader. Consequently, the reversal points at which the stranding direction of the optical transmission elements changes can be established by a reader through the cable jacket if markings in the form of aluminium labels, magnetic labels or RFID transponders are used. 
         [0059]    In the case of the arrangement  2  for producing an optical cable that is shown in  FIG. 2 , an armouring winding device  8000  may optionally be located upstream of the extruding device  7000 . Such an arrangement  3  for producing an optical cable is shown in  FIG. 3 . By means of the armouring winding device  8000 , an armouring  800  can be arranged over the sheath  200  and the markings  300 . Strips of aluminium, strips of steel or thin filaments of glass yarn or aramid, for example, may be arranged around the sheath  200  and the marking  300  as armouring elements. The armouring serves for relieving the cable core of tensile loads that act on the cable. 
         [0060]    In the case of an optical cable which comprises an armouring composed of metallic components, markings on the sheath  200  that likewise comprise a metallic material cannot be detected. Therefore, in the case of such a cable it is necessary to provide a marking, for example a coloured identification, on the cable jacket  700 . To provide the cable jacket with an identification, the arrangement for producing an optical cable that is shown in  FIG. 3  comprises an identification device  9000 , which comprises a detecting unit  9100  and a printing unit  9200 . The detecting unit is arranged upstream of the armouring winding device  8000 , in order to determine the marking still more reliably. The detecting unit  9100  may, for example, be formed as a metal detector, which detects the metallic labels  300  attached on the inner side  201  of the sheath  200  as they run past. The detecting unit may also comprise a magnetic detector, which is formed for the purpose of detecting a magnetically acting marking  300  as it runs past. Furthermore, the detecting unit  9100  may include a reader for detecting an RFID transponder. This makes it possible to detect markings in the form of transponders. 
         [0061]    In the case of a possible embodiment, the detecting unit  9100  is coupled with the printing unit  9200 . If the detecting unit  9100  detects the marking  300  on the sheath  200 , the printing unit  9200  is activated by a control signal SD, which is generated by the detecting unit  9100 . The printing unit  9200  is formed in such a way that, when the printing unit  9200  is activated with the control signal SD, a coloured identification is applied to the cable jacket  700  by the printing unit  9200 . 
         [0062]    The distance between the detecting unit  9100  and the printing unit  9200  may, for example, be an integral multiple of the interval between the reversal positions. This ensures that the cable jacket has an identification at every reversal position at which the direction of rotation with which the optical transmission elements are stranded changes. If the distance between the detecting unit  9100  and the printing unit  9200  deviates from a multiple of the interval between the reversal positions, the application of the identification to the cable jacket may take place with a time delay with respect to the activation of the printing unit by the control signal SD. In the case of the arrangement for producing an optical cable that is shown in  FIG. 3 , the provision of the cable jacket with an identification may take place with a deviation in a range from 0 mm to +/−50 mm with respect to the reversal position.