FR2570510A1 - METHOD FOR MANUFACTURING AN OPTICAL FIBER CABLE, AND CABLE OBTAINED BY ITS IMPLEMENTATION - Google Patents

Abstract

THE INVENTION RELATES TO THE MANUFACTURE OF CABLES CONTAINING OPTICAL FIBERS. IT RELATES TO A PROCESS ACCORDING TO WHICH WIRES FORMING LAYERS OF REINFORCEMENT G AND H, CONSTITUTED OF STEEL FOR EXAMPLE, ARE PLACED AROUND AN E TUBE IN WHICH OPTICAL FIBERS WERE PLACED WHEN IT WAS HOT SO WELL THAT, AFTER COOLING, THE OPTICAL FIBERS B SHOW A RELAXATION OF THE STRESSES WITH RESPECT TO THE LAYERS OF REINFORCEMENT G, H. APPLICATION TO THE MANUFACTURING OF CABLES INCLUDING OPTICAL FIBERS, IN PARTICULAR SUBMARINE CABLES.

Description

The present invention relates to formed cables

of optical fibers.

  Optical fiber cables, for example for submarine telecommunications or aerial cables containing optical fibers, must as far as possible isolate the optical fibers from the tensile stresses applied during the laying of the cable.

  on the bottom of the sea and possibly during the recovery

  when it is to be repaired as a result of deterioration during use, in the case of an underwater cable, and the similar tensile stresses applied during the pylons,

  the cable may be subject to significant variations in temperature

  eratures between the summer and winter months.

  British Patent No. 1,461,151 discloses an optical fiber cable in which the fibers are arranged in a tube constituting a resistant member and the fibers have a length greater than that of the tube, the tube being arranged with play around the fibers so that the latter and the tube may have a relative displacement, the tensile and bending stresses applied to the cable being collected substantially only by the tube. This patent proposes the suppression of possible deformations of the fibers by using fibers whose length is greater than that of the casing member so that, when the tube is in fact subjected to deformations and lengthens, the excess length of fibers placed in the

  tube prevents the application of the stresses to the fibers themselves.

  same. A method used for the arrangement of this length in excess of fibers, proposed by this document, is the advance

  fiber collection in the tube at a higher speed than

  greater than the speed of manufacture of the tube.

  British Patent No. 1,487,464 describes elements

  optical fibers for use in the manufacture of optical fiber cables, in which each element comprises an optical fiber housed with clearance in a single tubular sheath to a fiber or a number of fibers, the fiber or fibers occupying an longer than that of the sheath itself, inside it. Two techniques are envisaged for this purpose. First, the sheath can be elongated during manufacture by applying tensile forces and then by relaxation of the sheath; in a variant, a

  heat treatment can be used, the sheath being

  held sufficiently hot when it leaves a cooling tank after extrusion so that when it cools at room temperature, it shortens considerably given the difference between the coefficients of thermal expansion of the material of the sheath and that of fiber or fibers. However, these fiber optic elements have a sheath that is simply intended to facilitate

  the handling of fibers during the manufacture of a cable.

  The sheath itself introduces virtually no tensile strength. The tensile strength which the cable must possess is given by a separate tensile strength member which, in the embodiment considered in the patent, is a robust cable formed of steel wires, placed in the center of the cable around it. of which are placed the elements comprising the optical fibers. In this arrangement, it is difficult to predict whether, in the completed cable, the stresses are removed in view of the forces that are inevitably applied to the elements comprising the optical fibers during the committing, during manufacture

  cable. For example, the sheaths can be stretched

  in the manufacture of the cable and in this case the finished cable no longer has excess fiber length. So, some fibers can finally have a significant relaxation

  constraints while others may have a relaxa-

  little or no, and a very

  plex and sensitive so that the excess length of the optical fiber, in the sheath having play, is preserved in

the cable finished.

  The present invention relates to an optical fiber cable providing relaxation of fiber stresses

  optical in a controlled and predictable manner.

  More specifically, the invention relates to a method of manufacturing an optical fiber cable in which an optical fiber or a packet of optical fibers is housed in a metal tube, the method comprising advancing the fiber or the fiber packet in the metal tube before closing the tube, characterized by the presence of a temperature difference between the closing tube and the fiber or fiber bundle, the tube being warmer

  fiber or bundle of fibers, so that the relaxation

  stress is at least 0.1%. -

  Other features, advantages of the invention

  tion will become more apparent from the following description,

  Referring to the accompanying drawings in which Figure 1 is a sectional view of an optical fiber cable made according to an embodiment of the invention, Figure 2 is a section of an overhead conductor.

  suspended, realized according to an embodiment of the invention.

tion; and

  FIG. 3 schematically represents a device

  cable manufacturing industry as shown in

  Figures 1 and 2, according to one embodiment of the invention.

  In FIG. 1, the cable comprises a packet of optical fibers comprising a member A formed of a steel wire

  having a high tensile strength and which, if

  may be coated with copper so that its conductivity

  is increased, and which is coated with a plastic material Al.

  Around the package-reinforcing member A, consisting of this wire, eight monomode B secondary-coated optical fibers are held in the form of a bundle with the reinforcement member A by a C-whipping. It is preferable to use a fibrous tape of "Kevlar" which, in the particular embodiment, has a denier

about 200.

  The bundle of fibers is housed with play in a

  tubular core formed of a tube E which, in this embodiment of

  sation, is made of aluminum. Tube E has only one

  slot E1 so that the packet of optical fibers is introduced

  duit into the tube before the closure of the tubular member.

  The tubular core has an internal diameter D. The package and the annular space delimited between it and the internal hole D of the tubular member E are

  exposed and filled with a waterproofing compound.

  A laminated sealing layer or a thin copper ribbon M, in a variant, bearing the reference F, is placed around the web member E. This ribbon or strip is fixed in a sealed manner so that it form

  a hermetic seal around the optical fibers.

  Two layers of elements having a high tensile strength and bearing the references -G and H are placed around the band or tape F. The first layer G has a relatively small number of relatively

  having a high tensile strength which, in combination with

  with a larger number of wires having a smaller outer diameter, support the core and provide the bonding so that an electrically conductive, crush-resistant tensile strength member is formed and gives the cable the resistance

  mechanical that he must possess. In the case of a sub-cable

  it may be a breaking strength of the

  A polyethylene sheath is extruded around the outside of the metal wires of the outer layer of the reinforcing member and directly into these wires, and forms an electrical insulation between the outside and the wires. electrical or power signals that can be transmitted along the central conductive core E when

the operation of the cable.

  Figure 2 is a section of a suspended overhead cable

comprising optical fibers.

  It comprises a longitudinal reinforcing member which comprises a first layer of steel wires 13 having a high tensile strength, placed around a split aluminum tube 11, the assembly being surrounded by a

  additional electrical conductor tubular configuration

  the wall comprising a layer of aluminum son 14 of larger diameter. A number of optical fibers 10 are housed inside the aluminum tube 11, the fibers being held together and supported as a package by a "Kevlar" whipping 9 similar to that used in the In the two cables described with reference to FIGS. 1 and 2, it is important that a relaxation of the constraints

  for fiber optics because the duration of use

  of these fibers is then prolonged by reducing or eliminating the tensile stresses applied to them, the stress corrosion being reduced or eliminated, and the safety load of the cable during assembly or repair is increased by reducing the constraints

actually suffered by the fibers.

  Referring now to Figure 3 which schematically shows a device for manufacturing cables

  Figures 1 and 2, providing stress relief.

  In FIG. 3, the fiber optic packet of the cable of FIG. 1 or FIG. 2 is conserved on a roll 20, and the metal section having a section C (E or 11) is conserved on a roll 21. The bundle of fibers enters through the open slot of the C-channel at a point where both elements enter an induction heating device 22. The latter heats the profile to about 100 C and rollers and a closure die are placed at the station 23 so that they close the slot of the

  profile. The closed profile and the fiber pack 24 are cooled

  then at room temperature and can be transmitted to the first committing operation or can be temporarily stored on a drum. The package 24 enters a committing machine in which a first layer of metal wires G or 13 is applied around the profile. In the case of the cable of FIG. 1, the band or the band F is applied from an F1 bobbin before

  the first reinforcing member layer. This is represented

  The station 25 applies the first layer of metal wires in a conventional manner.

  and the package 24 or 24A having the first layer of metal wires

  (G or 13) progresses as indicated by reference 26 to the second committing machine 27 in which aluminum alloy wires 14 are applied in the case of the cable of FIG. 2 or a second layer of wires of FIG. H steel having a high tensile strength, forming a reinforcing member, is applied in the case of

cable of Figure 1.

  In the case of the cable of FIG. 1, a layer of polyethylene J is then extruded, and an outer layer K of shielding is applied in a conventional manner. The subsequent thermal shrinkage of the metal with respect to the fibers, due to the positive temperature difference between the metal section and the fiber bundle, reveals an excess

  of length in the fibers, in the finished structure.

  In fact, given the difference between the coefficients of thermal expansion of silica glasses and metals (approximately 10 6 and 10-5 / C respectively) the two sets can be adapted to high temperature and stress relaxation is however obtained at lower temperature or at room temperature. However, the effect of stress relaxation is less than that which is

  obtained by maintaining a positive difference in temperature

  erations at positions 22 and 23. It is found that a relaxation of at least 0.1% is necessary for useful protection.

fiber or fibers.

  For example, consider a formed aluminum tube

  around the fibers, ie the C-section.

  The thermal expansion of the aluminum is approximately 25 × 10 6 / OC. A stress relaxation of 0.25% can be obtained by shaping the tube at the previously indicated temperature of 100 ° C. above the temperature.

  ambient temperature or at the operating temperature.

  In the previous embodiments, the profiled aluminum tube acts as a member having a shrinkage and the shrinkage is actually "fixed" by application

  a reinforcing member around the profile.

  As the fibers are on the neutral axis of the frame, the intermediate storage on a roll of the section containing the fibers does not significantly affect the relaxation

constraints already ensured.

  The packet of optical fibers, in both embodiments, has a whipping around it and forms a

  limited thermal insulation layer which makes it easier to

  a positive temperature difference at stations 22 and 23 in FIG. 3. Thus, the packet of optical fibers,

  although it is subject to a certain extent to the temperature

  aluminum tube, when heated by the

  22 does not reach 100 C,

sence of the insulation layer.

  Better thermal insulation can be obtained

  application on the fiber optic package, of a rubber

  impregnating silicone rubber. Thus, as indicated in FIG. 3, an operation for applying an insulation

  thermal area marked by the rectangle 30, can ensure the

  the package or, in the case of a single fiber, can simply coat the fiber, with a silicone rubber

for example.

  Although FIG. 3 does not show it, the station 22 has an injector of a waterproofing material inside the C-section before closing it.

  so that the water that can enter the profile at one

  deterioration of the cable, when used later, can not progress longitudinally along the cable. This waterproofing can be performed at regular intervals along the profile. Preferably, this waterproofing material has a very high viscosity at room temperature of use, for example from ten million centipoise to about 25 C, but can be easily injected at 100 C. This ensures an effective "gluing" of fiber bundle to the profiled tube but allows a relative creep over long periods, for example a few

  days. It can be seen that these properties of the imper-

  metabilization are important for the relaxation of

  The strands applied to the fiber, because it may not be exactly on the neutral axis of the cable given the clearance provided in the cable.

Claims (10)

  A method of manufacturing an optical fiber cable, wherein an optical fiber or fiber bundle (B) is housed in a metal tube (E), the method comprising introducing the fiber or fiber bundle in the metal tube before closing it,   the method being characterized in that it comprises the creation   a difference in temperature between the closing tube and the fiber or bundle of fibers (B), the tube (E) being hotter than the fiber or the bundle of fibers so that the fiber or bundle of fibers undergoes a relaxation of at least 0.1%. 2. Method according to claim 1, characterized in that a reinforcing member (G, H) is applied around the tube when it has cooled to room temperature or when the temperature of the reinforcing member is greater than that of the tube.   3. Method according to claim 1, characterized in that the tube (E) is heated during the injection of a waterproofing compound into the tube, and the heating   is also realized later when the tube is closed.   4. Process according to claim 3, characterized in that the subsequent operation during which the tube is closed uses a set of rollers which are heated.   and a closure die which is also heated.   5. Method according to claim 1, characterized in that the tube (E) is a C-section which is closed   so that it forms a tube of circular section.   6. Method according to claim 5, characterized   in that the tube (E) is formed of aluminum.   7. Method according to claim 1, characterized in that a layer of reinforcing wire   (G, H) is heated just before laying on the tube.   8. Process according to claim 7, characterized in that an insulation layer (J) is extruded onto the son of the reinforcing member.   9. A method according to claim 7, characterized in that a layer of highly conductive metal wires, for example copper or aluminum, is formed on the wire of the armature member.   10. Cable characterized in that it is carried out by carrying out the method according to claim 1.