Stuctures of fibre optical cables having an autoresistance to compression

The present invention relates to the field of optical fiber cables and in particular the reinforcing structures of such cables and fibers.

The optical fibers used for telecommunications by optical signals are elements based on silicates (glass or quartz) which are particularly fragile and do not withstand the efforts of weight, traction and compression. It is known to use reinforcement structures to constitute an optical fiber cable intended to cover long or short communication distances.

Patent FR-B1-2 728 694 in the name of the applicant teaches an elementary reinforcing structure in which at least one optical fiber is inserted in a rigid shell called a microcarrier, to form an optical module (or even micromodule) reinforced in order to limit fiber curvature and attenuation of optical signals.

Patent application no. FR-96 04185 in the name of the applicant teaches a more advanced structure in which optical modules (micromodules) are associated with rigid reinforcement modules (microrrengths) and molded in a polymer sheath to form a cable. The application essentially describes flat cables in which the micromodules and the micro-reinforcements are coplanar, the sheathed cable having a ribbon shape.

Documents DE-A1-32 32 108, EP-A2-0 328 409, EP-B1-0 428 036 describe other reinforced cable structures with coplanar optical modules.

Known cables have the disadvantage of having a high rigidity linked to structures intended to withstand compression and tensile stresses.

Ribbon cable structures also have torsional drawbacks on curved paths with a small radius.

Such drawbacks predominate in domestic applications, domestic cables having to withstand specific mechanical stresses due to the small radii of curvature in the housings, to interior cables, to thermal shocks and to overhead cables with elongation.

An object of the invention is to provide an optical fiber cable without the aforementioned drawbacks and in particular adapted to the specifics of domestic distribution.

This object is achieved according to the invention from a modular structure of fiber optic cable. The structure combines at least one flexible reinforcement module with a small number of optical modules. Each optical module is self-resistant in compression, the flexible reinforcement module being simply tensile resistant to preserve the overall flexibility of the cable.

Preferably, the reinforcement module is made up of wicks of uncured fibrils, unlike known rigid reinforcements which include wicks of mechanical reinforcement fibers assembled by means of thermosetting resin. With strands of uncured fibrils, the reinforcement module works essentially when the cable is subjected to a tensile force. As for the compression stresses, they are mainly supported by the self-resisting optical modules.

According to the invention, provision is made for making a modular optical transmission cable comprising several reinforcing and optical modules, each optical module comprising:<ul id="ul0001" list-style="dash" compact="compact"><li>a sheathed optical fiber, coated by</li><li>an intermediate layer of decoupling and by</li><li>a rigid shell forming a microcarrier,</li></ul> a reinforcement module being associated at least with an optical module, the modules being molded in an external sheath, with the particularity that a flexible reinforcement module is associated with self-resisting optical modules in compression in order to obtain a cable having a high flexibility joined to a high compression resistance.

According to a preferred embodiment of the invention, the reinforcement modules are formed from wicks of micro-fibers not hardened by means of resin.

It is planned, according to a particular embodiment of the invention, to obtain a concentric structure, by making an optical transmission cable comprising at least one optical module inserted in a tubular reinforcement module molded in an external sheath, the module tubular reinforcement being flexible, the optical module or modules being self-resistant in compression so that the cable has a high flexibility combined with a high compression resistance, each optical module comprising:<ul id="ul0002" list-style="dash" compact="compact"><li>a sheathed optical fiber, coated by</li><li>an intermediate layer of decoupling and by</li><li>a rigid shell forming a microcarrier,</li></ul> the tubular reinforcement module consisting of wicks of microfibers not hardened by means of resin and occupying an effective cross-sectional area of ​​the cable.

The invention is generally carried out with a modular optical transmission cable comprising several modules molded in an external sheath, the cable comprising at least one self-resistant optical module in compression associated with at least one flexible reinforcement module to have high flexibility joined to high compressive strength, each optical module comprising:<ul id="ul0003" list-style="dash" compact="compact"><li>a sheathed optical fiber, coated by</li><li>an intermediate layer of decoupling and by</li><li>a rigid shell forming a microcarrier,</li></ul> characterized in that the reinforcement module or modules consist of wicks of micro-fibers not hardened by means of resin, the reinforcement module or modules being formed from a filling of wicks occupying an effective cross-sectional area of ​​the cable.

Preferably, the reinforcing module wicks are covered on the surface with an adhesive material of the hot-melt type.

According to a variant of the preferred embodiment, the reinforcing module wicks have interstices filled with swelling powder or hot-melt in order to avoid penetration of moisture.

It is intended that an optical module also comprises a final coating of non-stick material with a thickness of the order of 100 to 200 microns, in order to allow sliding of the optical module in the external sheath, the coating or sheath being , preferably, flame retardant.

Various cable geometries are further provided according to the invention.

Other characteristics, objects and advantages of the present invention will appear on reading the description below and the accompanying drawings, given only by way of nonlimiting examples.

In the accompanying drawings:<ul id="ul0004" list-style="dash" compact="compact"><li>FIG. 1 represents a schematic cross-sectional view of an elementary optical module used according to the invention,</li><li>FIG. 2 represents a sectional view of a concentric monofiber cable according to a first embodiment of the invention,</li><li>FIG. 3 represents a sectional view of a concentric monofiber cable according to a second embodiment of the invention,</li><li>FIG. 4 represents sectional views of planar cables according to a third embodiment of the invention, three monofiber, bifiber and tetrafiber variants being illustrated respectively in FIGS. 4A, 4B and 4C,</li><li>FIG. 5 represents a sectional view of a two-fiber cable according to a fourth embodiment of the invention,</li><li>FIG. 6 represents sectional views of cylindrical two-fiber cables according to a fifth embodiment of the invention, three variants being illustrated in FIGS. 6A, 6B and 6C,</li><li>FIG. 7 represents sectional views of cylindrical tetrafibers cables according to a sixth embodiment of the invention, two variants being illustrated in FIGS. 7A and 7B,</li><li>FIG. 8 represents sectional views of pentafiber cables according to the invention, a pentafiber variant of the sixth embodiment being illustrated in FIG. 8A, a pentafiber cable according to a seventh embodiment being illustrated in FIG. 8B,</li><li>FIG. 9 represents sectional views of rush cables according to an eighth embodiment of the invention, an embodiment of tetrafiber cable and an embodiment of octofiber cable being illustrated respectively in FIGS. 9A and 9B.</li></ul>

We will distinguish in the following description two types of fibers, optical fibers and reinforcing fibers which beyond their texture have different functions, the first being intended to transmit optical signals, the second having a mechanical reinforcement function. first and resistance to stresses exerted on the cable in general.

This distinction is found in the optical module and reinforcement module that make up the modular optical transmission cable.

However, according to the invention, it is planned to adopt optical modules having in themselves a reinforcing structure allowing them to withstand compression stresses.

FIG. 1 thus illustrates the elementary structure of an optical module 10 which is self-resistant in compression. The optical module 10 consists of a micromodule 11, a thin layer 3 of decoupling material and a rigid shell 12 called a microcarrier.

The optical fiber 1 of the micromodule 11 is a monomode or multimode silica guide typically having a diameter of 0.125 mm, preferably covered with a cladding 2. The sheathed fiber 11 has for example a diameter of 0.25 mm.

The intermediate decoupling layer 3 consists of a formulation of thermoplastic polymer.

The microcarrier 12 consists of a shell 4 preferably covered with another thermoplastic sheath 5.

Such an optical module structure 10 is analogous to the micromodule described in patent FR-2,728,694.

Note however that the shell 4 is preferably made of composite material based on fibers reinforced by polymerization, and that its diameter reaches for example 0.9 mm. The diameter of the optical module 10 is more generally of the order of 0.7 to 1 mm and reaches 1.2 mm with the alternative of a final sheathing coating 5.

&gt; The composite material is formed from glass fibrils of 5 to 10 microns in diameter gathered in wicks and hardened with resin to form a rigid shell 4. The resin preferably consists of polymers of the polyester, vinylester, epoxy or polyurethane type.

Thus, a rigid shell 4 is obtained capable of advantageously absorbing the compression stresses.

Indeed, the thickness of such a composite shell 4 gives the optical module a resistance to elongation of the order of 150 to 400 N measured for an elongation of 1% and a resistance to crushing greater than 15000 N m^-1. We also note that a straw effect appears only at a radius of curvature less than 15 mm. It will also be noted that with an optical fiber sold under the reference G652 or the like, the optical attenuation undergoes variations of less than 0.1 dB in a temperature range of between + 70 ° C and -10 ° C, the variations remaining below 0.5 dB between -10 ° C and -30 ° C.

The technical specifications of the overhead optical cable which it is sought to achieve, however, are higher. As an indication, an elongation resistance of at least 500 N measured for an elongation of 0.3% is sought.

The invention therefore provides for constituting a cable by associating one or more self-resisting optical modules in compression with one or more flexible reinforcement modules, a flexible reinforcement module being essentially intended to resist tensile forces.

Such an arrangement is opposed to the known structures of optical cables in which the reinforcements alone support all the mechanical stresses and must be rigid to resist the stresses of compression and traction.

An advantage of the structure according to the invention is the flexibility of the cable obtained. Indeed, the most rigid element of the structure, the shell 4, has a reduced diameter, and by mechanical principle, the influence of this element on the stiffness of the cable is minimized.

Another advantage of the cable structure according to the invention is the lightness of the cable resulting from the adoption of flexible reinforcement modules. Unlike known reinforcements which are loaded with polymer resin and dimensioned to resist compressive stresses, a flexible reinforcement module preferably consists of wicks of fibrils which are not hardened by means of resin, and therefore lighter.

The reinforcement module is generally formed of microfibers bonded in the form of wicks without bonding or hardening using resin.

Microfibers are made of a material with a high Young modulus, such as carbon, aramid, ceramic, polymers, glasses of type E, R, S or a combination of fibers of such materials.

The microfibers (or fibrils) have a diameter close to a micrometer but the wicks formed can be of various dimensions. The number and size of the microfiber strands are chosen so that the resistance R of a single-module cable is preferably greater than 170,000 N, the resistance R being given by the following formula:<maths id="math0001"><math display="block"><mrow><mtext>R = ES</mtext></mrow></math><img file="EP0902310A1_D0001.tif" /></maths> where E is Young's modulus, and S is the area effectively occupied by the strands of fibers on a cross section of the module. Preferably, the microfibers are treated on the surface to reveal free chemical groups having a function of attraction of the fibers between them (bonding by hydroxyl radicals). In addition, the wicks of the module formed are preferably covered on the surface with an adhesive material of the hot-melt type deposited hot after forming the wicks. The term "hot-melt" is used to describe any hot-melt adhesive and the hot-bonding technique known to those skilled in the art. The adherent material consists, for example, of ethylene vinyl acetate, polyamide, neoprene, nitrile rubber or a combination of such materials. The fibers are thus moderately bonded.

An advantage of such a reinforcement module based on uncured fibers is that it resists traction without impairing the flexibility of the cable.

As the wicks of fibers are not filled with resin, the invention further provides for filling the interstices of the wicks with swelling powder or simply hot melt in order to avoid penetration of moisture into the cable.

According to the invention, the cable consists of a combination of reinforcing and optical modules, an external sheath retaining or molding the modules.

The various assembly geometries of modules and external sheath are the subject of several embodiments set out below.

Still generally, the outer sheath is formed of a polymer material with a high Young's modulus deposited by extrusion or by pultrusion on the assembly of modules.

The external sheathing material is preferably a high density polymer, of the polyethylene, polyamide, polyester, polyether-ether-ketone, polyether imide, polyether sulfone or equivalent type. Polyvinyl chloride loaded or polyolefins loaded in particular with glass beads or microfibers can also constitute the external sheath.

The sheathing material typically has a Young's modulus of 1000 MPa to 5000 MPa under the conditions of use in order to contribute to the resistance of the cable.

FIG. 2 illustrates a simple embodiment of a fiber optic cable that is self-resistant to compression according to the invention.

The monofiber cable 200, according to this first embodiment, comprises a single axial optical module 10, with the constitution described above with reference to FIG. 1. The optical module 10 is coated directly with wicks of fibers forming a flexible reinforcement module 20 tubular according to the invention. The modules 10, 20 are finally molded in an external sheath 21.

According to a first non-limiting example of embodiment, the tubular reinforcement module 20 has internal diameters of 1.2 mm and external diameters of 2.2 mm, the thickness of microfiber strands then being 0.5 mm. In this first example, the external sheath 21 has a thickness of 0.7 mm, ie a final cable diameter of 3.6 mm. This gives a monofiber cable 200 having a resistance greater than 500 N measured for an elongation of 0.3%.

In a second embodiment of a monofiber cable 200, the tubular reinforcement module 20 has internal diameters of 1.2 mm and external diameters of 2 mm, the thickness of wicks being limited to 0.4 mm. The outer sheath 21 has a thickness limited to 0.5 mm in this second example, ie a final cable diameter of 3 mm. One then obtains a monofiber cable 200 having a resistance of 500 N measured for an elongation of 0.6%. The cable produced according to this second example has the advantage of being compact and light.

Such lightening of the cable structure, with a reduction of the order of 20 to 50% in the number of fibers and in the cross-sectional area actually occupied by the strands of fibers, can be applied each time that a fiber elongation 0.6% is acceptable. The lightening with reduction of surface of wicks of fibers is applicable in particular to the other embodiments below.

FIG. 3 represents a second embodiment in which a concentric structure of monofiber cable 300 close to cable 200 is adopted.

Unlike the first embodiment, an intermediate casing 13 is provided, according to the invention, between the axial optical module 10 and the peripheral reinforcement module 30. The tube 13 consists of a plastic material chosen in particular from polymers such as polyvinyl chloride and polyolefins loaded. The plastic material is preferably flame retardant, for example by treating it with alumina hydrate or another fire-resistant substance, and free of halide (chloride, fluoride, bromide) to prevent toxic fumes.

The plastic tube 13 has a wall thickness of the order of 0.5 mm. The tube 13 has for example internal diameters of 1.3 mm and external diameters of 2.3 mm as shown in FIG. 3.

An advantage of the second embodiment is the excellent compressive and shear strength of the cable 300 obtained. The casing 13 increases in particular the resistance to mechanical impact, radiation and physico-chemical attack. Such specific features make cable 300 particularly suitable for use in technical premises (tunnels, technical ducts, basements) and for wiring in front of buildings.

It will be noted, according to the previous dimensioning examples, that a sheathed optical module 10 (diameter 1.2 mm) is freely inserted into the tube 13 (internal diameter 1.3 mm). This arrangement allows the optical module 10 to have margins of movement as well in expansion, in sliding, or even in retraction if it is intended to give it play during manufacture.

In addition, the final sheathing coating 5 of the optical module 10 is preferably made of a non-stick material, in order to allow sliding of the optical module in the tube or more generally in the cable. The non-stick material may in particular be a polyamide, polyester, polyether sulfone, polyether ketone or polyether imide material. This final coating 5 covering the module 10 can possibly be fireproofed.

FIG. 4 represents a third embodiment of the cable in which the modules are substantially coplanar axes.

According to the invention, a single flexible reinforcement module 40 of cylindrical shape is arranged laterally and with spacing relative to the associated optical modules.

FIG. 4A thus shows a monofiber cable 401 comprising a reinforcement module 40 and an optical module 10 molded in the outer sheath 41. The module 40 and the module 10 are spaced and the sheath molding has one or two longitudinal grooves 42 hollowed out along the median axis of spacing of the modules 10 and 40. Such an arrangement makes it possible to easily separate the optical module 10 and the reinforcement module 40 for domestic connections. Another advantage of such an arrangement is that on an aerial portion, the cable 401 can be fixed by tightening an attachment clip on the side reinforcement module 40 without damaging the optical module.

The grooving 42 is however optional, the sheath may have a solid section, in particular rectangular or oval.

By way of non-limiting example of sizing, the cylinder of microfiber wicks constituting the reinforcement module 40 has a diameter of 1.5 mm, the optical module 10 having a diameter of 1.2 mm; the outer sheath 4 of high density polyethylene has a thickness greater than 0.4 mm. The cable obtained according to this example has dimensions in total width of 4.7 mm and in total thickness of 2.3 mm.

A cable 401 is thus obtained having a resistance to elongation greater than 500 N measured for an elongation of 0.3%.

FIGS. 4B and 4C illustrate two variants of cables with coplanar modules, a bifiber cable 402 being illustrated in FIG. 4B and a tetrafiber cable 403 being illustrated in FIG. 4C.

One can use modules 40, 10, 10 ', 10 ", 10'" and an external sheathing 41 having the same dimensions as in the example concerning the cable 401.

A cable 402 is then obtained having a width of 5.7 mm and a resistance greater than 600 N with an elongation of 0.3%. The cable 403 has a width of 8.3 mm and a resistance greater than 750 N measured for an elongation of 0.3%.

An advantage of the cable obtained according to the third embodiment is its lightness.

According to the previous examples, the linear density of the 401 monofiber cable is less than 8 gm^-1 while the linear mass of the 403 tetrafibre cable is less than 12 gm^-1 or a third of the linear mass of a small overhead electrical copper cable.

The optical modules 10, 10 ', 10 ", 10'" are preferably placed side by side and a bonding 43 can be provided at their contact zone to improve the assembly of the modules 10, 10 ', 10 ", 10 '"between them and possibly with the sheath 41.

FIG. 5 illustrates a fourth embodiment of the invention in which several self-resisting optical modules 10, 10 ′ are embedded in a flexible reinforcement module 50, the assembly being covered with an external sheathing 51.

The optical modules 10 and 10 'can be glued for example by means of a thin layer of EVA type hot-melt which allows to jointly extend but also to easily separate the modules 10 and 10' when wiring and domestic connections .

The reinforcement module 50 surrounds and fills the interstices between the optical modules to obtain an ovalized section having for example a thickness greater than 0.3 mm of wicks of fibers. The external surface of the reinforcement module 50 is covered with an external sheath having for example a thickness of 0.5 mm.

The cable 500 thus formed has a section with a major axis D of 4 mm and a minor axis E with 2.8 mm. A resistance greater than 600 N is then obtained for an elongation of 0.3%.

An advantage of the cable 500 is its simplicity of manufacture and operation.

FIG. 6 represents two-fiber cables according to a fifth embodiment in which the two self-resisting optical modules 10 and 10 ′ are associated with one or two flexible reinforcement modules 60 and 60 ′. Unlike the cable 500, all the modules 10, 10 ', 60, 60' and 63 of the cables 601, 602 and 603 are cylindrical and assembled in bundles, leaving gaps before the external sheathing 61.

As visible in FIG. 6A, the cable 601 has a cylindrical section of revolution, the external sheath 61 forming a circular crown.

The bundle disposed in the lumen of the cable 601 comprises two optical modules 10 and 10 'in contact or glued and two reinforcing modules 60 and 60' on either side of the optical modules. With, for example, optical modules having a diameter of 1.2 mm, reinforcement modules having a diameter of 1 mm, and a sheath having a thickness of 0.5 mm, a cable 601 having a diameter of 3.4 is obtained. mm and having a resistance greater than 600 N for 0.3% elongation.

Lighter cables can be obtained by reducing the section actually occupied by the fibers of reinforcement modules, as illustrated in FIGS. 6B and 6C.

FIG. 6B represents a cable 602 comprising, unlike cable 601, two smaller reinforcement modules and an external sheath 62 of oval cross-section.

With, for example, two cylindrical reinforcement modules having a diameter of 0.6 mm, and a sheathing of thickness of 0.5 mm, a cable is obtained having an elongation resistance of 600 N measured for an elongation of 0, 6%.

FIG. 6C represents a cable 603 of ovalized section in which, unlike cables 601 and 602, the two reinforcement modules 60 and 60 ′ have been replaced by a single reinforcement module 63.

With a bundle comprising two optical modules 10, 10 ′ and a round reinforcement module 63 having for example a diameter of 1 mm, covered with oval sheathing of thickness 5 mm, a cable is obtained having a resistance of 600 N measured for a 0.6% elongation.

FIG. 7 represents tetrafibers cables 701 and 702 produced according to a sixth embodiment of the invention. The cables 701 and 702 also include a bundle of self-resisting optical modules 10 and flexible reinforcement modules 70 covered with a cylindrical sheathing 5 which circles the bundle leaving gaps.

The cable 701, illustrated in FIG. 7A, comprises a bundle comprising a single central reinforcing module 70, cylindrical, and four optical modules 10, 10 ', 10 "and 10"' arranged regularly around the reinforcing module 70.

The cable 702, illustrated in FIG. 7B, is a variant with a bundle comprising five reinforcement modules 70, 70 ', 70 ", 70"' and 70 "". Four reinforcement modules 70 'to 70 "" are added at the periphery of a bundle similar to the bundle 70, 10, 10', 10 ", 10" 'of the cable 701. One such cable with five reinforcement modules 70 to 70 " "has a high resistance.

With flexible reinforcement modules 70 having a diameter of 0.5 mm and a sheathing of 5 mm, a cable 701 having a resistance greater than 700 N is obtained for an elongation of 0.6% and a cable 702 having a resistance greater than 700 N for an elongation of 0.3%.

FIG. 8 represents pentafiber cables 801 and 802 produced according to the invention.

The cable 801, illustrated in FIG. 8A, comprises, like the cable 701, which is the subject of the sixth embodiment, a bundle with a single central reinforcement module 80 and with five optical modules 10 to 10 "".

The cable 802, the object of a seventh embodiment comprises a central overfilling of reinforcing wicks as a flexible reinforcement module 82. The core 82 of the bundle therefore consists of a filling of wicks of aramid microfibers or of other material around which the five optical modules 10 to 10 "" are regularly arranged.

An advantage of the 802 cable structure is its high crush resistance.

Preferably, provision is made to cover the surface of the reinforcement module 82 with a layer 83 of adhesive material to secure the modules 82 and 10 to 10 "". The adhesive layer 83 has a small thickness, of the order of 50 to 200 microns for example. The adherent material preferably consists of hot-melt based on ethylene vinyl acetate, polyamide, neoprene or nitrile rubber.

Such an arrangement has the additional advantage of allowing great deformation of the cable during installation before the modules are mechanically stressed.

As an example of an embodiment, the overfilling of fibers constituting the reinforcement module 82 has a radius varying between 0.5 and 1.1 mm, the cable having a diameter of 4.8 mm.

Finally, FIG. 9 represents an eighth embodiment of the invention in which the optical modules 10 are arranged on the periphery of a central rod 100 in grooves recessed on the surface of the rod 100. The rod preferably consists of a thermoplastic or thermosetting material based for example on polyolefin, polyamide or polyesters.

As visible in FIG. 9A representing a tetrafiber cable 901, the four grooves 110 to 110 "'are preferably with rounded bottom and the rod does not have a central reinforcement. Indeed, a flexible reinforcement module 90 of tubular form covers the rod 100 after insertion of four optical modules 10, 10 ', 10 "and 10"' in the grooves 100, 110 ', 110 "and 110"' respectively.

By way of nonlimiting example, the thermoplastic rod 100 has a diameter of 3.8 mm, the grooves being adapted to receive the optical modules 10 of diameter 1.2 mm.

The central framework of the rod 100 with the bundle of optical modules 10 is covered with a reinforcing module 90 formed of a layer of fibers having a thickness of 0.3 mm and finally with an outer sheath of thickness 0, 7 mm. Such a cable with a diameter of 5.8 mm has a resistance greater than 700 N for an elongation of 0.3%.

An advantage of such a framework is the high crushing resistance imparted to the cable.

FIG. 9B shows an octofiber cable 902 according to the eighth embodiment of the invention, of structure similar to cable 901.

By way of nonlimiting example, the cable 902 comprises a central rod 100 with a diameter of 5.5 mm, eight self-resisting optical modules 10 with a diameter of 1.2 mm, a flexible reinforcement module 90 formed by a layer of wicks 0.25 mm thick fibers and finally an outer sheath 0.7 mm thick.

Such a cable 902 has a diameter of 7.4 mm and has an elongation resistance greater than 800 N corresponding to an elongation of 0.3%.

In conclusion, the optical cable structure provided by the invention is declined according to eight nonlimiting embodiments, and has the advantage of combining flexibility and high tensile and compressive strengths.

It also has clear advantages of lightness, its linear mass being notably less than that of copper electrical cable. An important advantage of the embodiments of cables according to the invention is the ease of manufacture. Consequently, the manufacturing cost is very reduced.

In addition, the laying of such cables is easy. Indeed, this light structure requires a low aerial laying tension adapted to the commonly used hooking clips. On the other hand, the modular structure makes it easy to separate the optical modules intended for each subscriber.

The laying of optical cables according to the invention is made as simple as the laying of electric wires and the installation can be carried out quickly by a single technician.

Such characteristics and advantages of the optical cable according to the invention are particularly favorable for domestic and multi-use cabling.

Other applications, variants and characteristics of the invention will appear to a person skilled in the art without departing from the scope of the invention and the claims below.