FR2555326A1 - Optical cable especially for connection and process for manufacturing such a cable - Google Patents

Abstract

a. The invention relates to an optical cable especially for connection and a process for manufacturing such a cable. b. The cable is characterised by at least one tube 5, 6 of shape corresponding to that of the cross-section of a groove 3, 4, which tube is housed in a groove 3, 4, in order to receive an optical fibre 9, 10. c. The invention relates to optical fibres.

Description

"optical target including connection and method of
making such a cable "
The present invention relates to an optical cable, in particular an optical connection cable composed of a rod with in its center a carrier element with a high modulus of elasticity, the rod being provided with helical grooves in its peripheral surface for receiving fibers optics together being surrounded by tape or cladding.

 The invention also relates to a method of manufacturing such an optical cable.

 Optical cables of the above type are already known as well as their manufacturing process.

 In general, fiber optic cables have grown very rapidly in recent years; these cables fall into two categories, tight fiber cables and free fiber targets.

 In tight fiber cables, the fibers are coated with several successive layers of increasingly hard materials. These fibers are not very sensitive to micro-bends and very little sensitive to lateral reactions caused by axial traction. On the other hand, these fibers undergo all the elongations imposed on the cable by the environment, which results in permanent fatigue which shortens their lifespan without deteriorating the characteristics of the transmissions.

 In loose fiber cables, the fibers are housed in the grooves of a rod or in tubes, so that the fibers are not subjected to dimensional variations of the rod or tubes. In general, the fiber section is relatively small compared to that of their housing (groove or tube) and the above decoupling effect results from the slight length of the fiber compared to its housing.

 Optical tube cables consist of a bundle of tubes, each containing an optical fiber.

These bundles are brought together to form a cable. In the case of rod cables, the rod provided with a longitudinal reinforcement intended to receive the tensile forces comprises helical grooves in which are deposited each time a fiber and together is surrounded by a sheath or a taping to maintain the fibers in the grooves. The latter type of optical cables is described in particular in French patents NO 79 30 004, 82 21 760 and 83 04 864.

 Among the cables described briefly above, those formed by a bundle of tubes are of relatively practical use for separating the fibers and making the junction with subscribers, each subscriber being, in general, connected to a single fiber. Indeed, just open the target to remove the sheath and separate the tubes containing the fibers.

 This connection operation is much more difficult in the case of rod cables in which the fibers are free when the sheath is removed and the rod is cut. It is necessary, in this case, to provide an intermediate piece called "octopus", composed of a head intended to cover the end of the optical cable and of tubular arms each receiving a fiber. This covering piece currently distributed under the name bursting octopus ", manufactured by the company SILEC, is interesting. However, the implementation of this technique is relatively delicate and long. For example, the use of such an octopus for the end of a ten-fiber cable, is done in ten minutes in the laboratory and in 30 minutes on site. r, it was found that this implementation time, relatively important for a ten-fiber cable, is not reduced significantly for a cable having a smaller number of fibers.

 As a result, this implementation time becomes prohibitive for a two-fiber cable.

 In conclusion, among the optical cabals currently existing, the one which is the most interesting, namely the armored rod cable with helical groove containing free fibers, is not satisfactory as a connection cable, when it has to be burst towards the different users.

 The present invention proposes to create an optical cable in particular a connection cable intended for exploded purposes to allow the connection of several subscribers, the implementation of which on site, at the location of the burst, is particularly simple, without however reduce the optical characteristics of the cable.

 To this end, the invention relates to a cable characterized by at least one tube of shape corresponding to that of the section of a groove, the tube housed in a groove for receiving an optical fiber.

 The expression tttubett used above and in the following description designates an element which in its final form, at least after its installation is a tube or part of a tube. In fact, this tube which can have a function of guiding the fiber, in particular in the case of a star-shaped rod whose grooves have a non-circular section, also play the role of a tubular support element for the fibers. in the part without the rod, between the cut end and the connection point at the subscriber's. Besides, following the path to follow, it may be interesting to accommodate this tube containing the optical fiber in a protective sheath in the manner of an electric cable. However, in general according to an interesting characteristic, the tube is selected in the group formed by the closed extruded tubes, open extruded tubes, open extruded tubes with overlapping edges, tubes formed by a gradually folded strip to form a tube.

 The connection cable thus produced is particularly interesting because it offers all the interesting characteristics for the operation of an optical cable since the optical fibers are free and do not undergo any of the tensile forces which are all received by the rod and its core or element carrier. The connection of subscribers, that is to say 11 bursting of the cable and the opening of its end to separate the various optical fibers is very simple and rapid, even on site. From the bursting point or measure a length of cable corresponding to the greatest length of fiber required, then, after removal of the sheaths and ribbons, the tubes containing the fibers are extracted from the grooves until the bursting point; this allows the rod and the friend to be cut without risk to the tubes and fibers. Then simply simply connect the different tubes to subscribers or other users.

 According to another characteristic, the tube is held by the shape in its groove of the rod, the tube is fixed integral in its respective groove with the rod, in particular by a point bonding, the retention of the tube in its throat by a connection by the form is a solution. particularly advantageous in the case of a circular cylindrical tube and a groove whose opening is significantly less than the diameter of the tube.

 This solution is particularly advantageous in the case of a tube produced on the spot in the groove from a ribbon which is progressively shaped into an open tube or whose lips overlap.

 Interestingly, the rod provided with a core has a star-shaped section whose branches define between them the grooves receiving the tubes for the optical fibers.

 As already indicated above, such a rod is a very interesting achievement. In addition, as the grooves have a non-circular section, the tube placed and fixed in each groove constitutes the actual housing of the free fiber and does not transmit any of the stresses otherwise exerted on the rod.

 The invention also relates to a method for manufacturing such a cable.

 The method is characterized in that in at least some of the helical grooves of a rod provided with a longitudinal reinforcement, a tube is deposited and in each tube thus placed in a respective groove, an optical fiber is deposited.

 It is particularly important that the optical fiber is placed in the tubular element after the latter has been placed in its groove of the rod and not the reverse. Indeed, the deterioration of the optical characteristics of an optical fiber is particularly sensitive to tensile forces. Thanks to the positioning of the tubular element in the groove of the rod before the optical fiber is placed in the tube, the optical characteristics of the fiber are not deteriorated since the latter is placed in the cable blank thus carried out. This establishment can, moreover, be done with a determined extra length which it would not be possible to define precisely if the fiber was in the tubular element before the establishment of this in the groove of the rod.

 According to a particularly advantageous characteristic, the substantially cylindrical tubes are deposited, which are opened and kept open upstream of the point of spite P of the corresponding optical fibers and which are again closed at F downstream of the point of deposition of the optical fibers. .

 The opening of the tube after its deposit in its groove is done using a cutting tool if the tube is closed or by a simple rod or blade inserted between the two edges which touch or overlap in the case of a tube not yet definitively closed. The process is similar in the case of a tube produced from a flat ribbon gradually shaped.

The present invention will be described in more detail with the aid of the accompanying drawings in which
- Figure 1 is a sectional view of a cable with two optical fibers, according to the invention
FIG. 2 is a perspective view of the end of an optical cable having a burst point
- Figure 3 is a sectional view of a cable according to Figures l and 2 during manufacture
- Figure 4 is a view of another embodiment of a cable according to the invention
- Figures 5A, 5B, 5C, 5D show different embodiments of tubular elements, according to the invention
- Figure 6 is a schematic view of an installation for implementing the method, according to 1I in vention.

 Figure I shows a fiber optic cable with two fibers.

 The cable consists of a rod I provided with a frame or a central support element 2 with a sort elasticity module intended to transmit the tensile forces.

In two symmetrical positions with respect to the tax, the rod 1 comprises two grooves of circular section 3, 4 each provided with a tubular element 5, 6, for example closed by a weld or a bonding line 7, 8 and containing a optical fiber 9, 10. The assembly is surrounded by a protective tape 11 itself surrounded by a first and a second protective sheath 12, 13.

 The tubular elements 5, 6 have a section shape corresponding to that of the cells 3, 4. In the present case, the cells have a circular section and the tube elements 5, 6 also have a circular section. It is, however, to be noted that the opening of the groove of circular section 3, 4 is less than the diameter of the section so as to retain mechanically or by shape, the tubular elements 5, 6 in the grooves 3, 4. The same remark applies for other forms of groove section. The fixing of the tubular elements 5, 6 in the grooves 3, 4 can also be carried out by a punctual bonding at bonding points in the longitudinal direction of the cabal. This joining can also be done mechanically, by projecting elements provided on the tubular elements 5, 6, and coming to be housed in cavities of corresponding shape of the groove 3, 4 of the rod. The important thing in this assembly is that the tubular elements 3, 4 are secured to the rod to avoid any relative movement during the positioning of the cable, when the latter must follow non-rectilinear paths, to avoid that the erratic constraints which could be exerted on the tubular element are not transmitted to the optical fiber housed in the tube.

 Figure 2 shows 11 end of such an optical cable, prepared for connection. This end has been stripped, leaving only the taping 1 which still remains at the end of the rod I.

This rod has been cut and reveals the tubular elements 5, 6 and the optical fiber 9, 10 contained in the tubular elements 5, 6. In this figure, the length of the tubular elements 5, 6 which protrudes from the cut end of the rod 1, has been shown very short. In fact, this remaining length varies according to the distance to be covered, which can be of the order of a few decimeters to a few meters.

 Figure 3 is a sectional view of the rod of a cable during manufacture. This figure shows the rod 1, the core 2, the cells 3, 4 and strips 5 ', 6' intended to form the tubular elements. These bands are open and only the middle part of each of the bands has taken a circular cylindrical shape.

 The lips 5'a, 5tb and 67as 6tb of the strip have not yet been joined together to the other. This figure also shows the optical fibers 9, 10 put in place before the tubular elements are closed.

 The sectional view of Figure 4 corresponds to another alternative embodiment of an optical cable according to the invention.

 In this embodiment for example of an optical target with five fibers, the rod is constituted by a central part 20 provided with a core 21 and with radial elements 22 defining grooves 23 each receiving a tubular element 24 intended to receive itself an optical fiber 25. With the exception of the particular shape of the rod 20, 21, 22 which is preferably manufactured by extrusion, and not by machining, the other elements of such a cable and of its manufacturing process are analogous to those described above and below.

 FIGS. 5A, 5B, 5C, 5D show different embodiments of a tubular element intended to receive an optical fiber.

 According to FIG. 5A, the tube 30 is extruded in the form appearing in the figure; it is split upstream of the point of removal of the optical fiber along the cutting line 31; the edges of the tube close again under the effect of the inherent elasticity of the tube 30, downstream of the point of removal of the optical fiber.

 FIG. 5B shows a tubular element 32 similar to that of FIG. 51 but the junction of the two cut edges of the tube 32 is made downstream of the point of removal of the optical fiber by a weld 33.

 The embodiment of FIG. 5C corresponds to a tube 34 whose edges 35. 36 overlap.

The opening of this tube 34 for the removal of the optical fiber is done mechanically by simple spacing of the two edges which return to one another under the effect of the inherent elasticity of the tube 34.

 FIG. 5D corresponds to a tube obtained by the successive folding of a strip 37 whose edges 38, 39 are progressively brought together to close the tube, for example by gluing or by welding the two edges.

 Figure 6 is a very schematic drawing of an installation for manufacturing an optical cable according to the invention.

 The installation consists of an input device 40 and an output device 41.

 The input device 40 receives the rod 42 and supplies it downstream at a constant speed, the output device 41 exerts on the part of the rod located between the device 40 and the device 41, a constant force.

 The combination of the devices 40, 41 makes it possible to transiently lengthen the rod (and the tubes) to deposit the fibers with a determined length. As the linear velocities of the rod in the elongated state and of the fibers at the place of removal are identical, when the rod retracts again at the outlet of the laying path, downstream of the device 41.

 In practice, the devices 40 and 41 may consist of two endless bands between which the rod passes. I1 can also be a set of cylinders or coils over which the rod or cable passes at the outlet of the installation.

 The production of the rod 42 with the grooves can be done by extrusion or by machining.

 Downstream of the input device 40 is a station 43 for laying the tubes 44, 45. The laying station 43 is followed by the station 46 for securing the tube or tubes and the rod which is optionally followed by a station for opening 47 of the tube or tubes in the case of tubes 44, 45 closed. This station is not used when the tubes 44, 45 are in fact constituted by ribbons initially flat and which are unwound in the grooves to gradually take an open tubular shape intended to receive the fiber and to be downstream of this laying station. closed to form tubes.

 Following the stations 46 and 47 is the fiber depositing station 48 in which the fibers 49, 50 are deposited at a point B in the tubes 44, 45 formed previously. Following the depositing station 48 is the station 49 for closing the tubes. This station is generally a device for depositing glue on the edges of the tubes, heat sealing or any other similar station.

In the case of a tube which closes elastically, the station 51 is not used. This station is followed by a taping station 52 and the output device 41. Following the output device, there may be one or more sheathing stations.

 The screen 53 thus produced is wound on a reel.

 In the description above, the diagram assumes the production of an optical cable with two fibers. However, the same installation can be used for any number of fibers. It should be emphasized that the points of deposit of the tubes (T), of joining tubes-grooves (S), of opening the tubes (0), laying of fibers (P), of closing of tubes (F) and of taping (R) are points which, according to a preferred embodiment, are fixed in space, the rod 42, the device 40, the cable blank 53. the outlet device 41, rotating around the axis of the rod following a uniform rotational movement corresponding to the speed of travel along the pitch of the heli-cotidal grooves produced in the rod 42.

 In each of the above stations, for example the drop-off points for the tubes, removal of the optical fibers, etc., that is to say the stations operating not at a single point but at as many points as there are of fibers, can title shifted in space, according to a fraction of step and remain fixed in the running conditions of the rod mentioned above.

 To be complete, the part of the installation described above only corresponds to the zone for depositing the tubes and fibers in the grooves of a rod. The part of the installation upstream and which supplies the rod can be either machining stations receiving the rod to cut the grooves therein or an extruder producing the rod on a support core. In the first case, the size tools preferably occupy a fixed position like the organs for depositing tubes and optical fibers downstream. In the second case, the extrusion nozzle also has a fixed position.

Claims (7)

 10) Optical cable, in particular an optical connection cable composed of a rod with in its center a carrier element with a high elasticity modulus, the rod being provided with helical grooves in its peripheral surface for receiving optical fibers, the whole being surrounded by a taping or sheathing, target characterized by at least one tube (5, 6), of shape corresponding to that of the section of a groove (3, 4) housed in a groove (3, 4), for receiving an optical fiber (9, 10).  20) Optical cable according to claim 1, characterized in that the tube (5 6) is held by the shape in its groove (3, 4) of the rod.  30) Optical cable according to any one of claims 1, 2, characterized in that the tube (5, 6) is fixed integral in its respective groove with the rod in particular by a point bonding.  40) Optical cable according to any one of claims 1 to 3, characterized in that the tube is chosen from the group formed by closed extruded tubes (30, 32), open extruded tubes, open extruded tubes with edges covering (36), the tubes formed by a folded strip (37), programmed to constitute a tube.  50) Optical cabal according to claims I to 4, characterized in that the rod (23) provided with a core (21) has a star-shaped section whose branches (22) define between them the grooves receiving the tubes (24) for optical fibers (25).  60) A method of manufacturing an optical cable according to any one of claims 1 to 5, characterized in that in at least some of the helical grooves of a rod provided with a longitudinal reinforcement (42), is deposited ( 43) a tube and in each tube thus placed in a respective groove, an optical fiber is deposited (48).  70) Method according to claim 6, characterized in that substantially closed cylindrical tubes are deposited, which are opened upstream of the point of spite (P) of the corresponding optical fibers (49, 50) and that one closes again (F) downstream of the optical fiber depot.