CA1135094A - Unitary cabling element for manufacturing optical fiber cable elements - Google Patents

Abstract

Abstract of the Disclosure There is disclosed a unitary cabling element for optical fibers, consisting of an elongated strip member of a resi-lient plastic material having a continuous bottom face and a series of spaced parallel recesses opening into the opposite face of the strip member by means of longitudinal channels of a substantially trapezoidal shape, the mating faces of which diverge outwardly with an included angle of 360°/n, n being the number of the recesses in the strip member. Optical fibers are loosely received within said recesses and the strip member is wound around an elongated central carrier in the configuration of a unitary cylindrical cable element with angularly spaced closed recesses therein. Said unitary cable elements may be juxtaposed in a bundle or concen-trically wound to form a high density optical fiber calbe. The cabling element may have an internal flat configuration or at least a partially cylindrical configuration.

Description

~35~
BA CKG~OUND OF l'HE I~ENTION

Field or the invention The invention relates to a new supporting structure or cabling element for optical fibers which can be used as such or for manufacturing cables containing a great number of fibers, for example communication cables Descripti~ of the prior art The brittleness of optical fibers with respect to mechanical, e.g tensile, torsional or compressive stresses, makes lo it difficult and costly to manufacture optical cables or cable ele-ments, more particularly high density cables having suitable trans-mitting features and which can be easily connected or interconnected.
various cables structures have been proposed originating from conventional cable constructions by making use in said structures of carrying or supporting elements in an attempt to limit or to suppress the mechanical stresses onto the fibers and possible resulting drastic deformations.
Some manufacturers have proposed strip-type struc-tures wherein the optical flbers are maintained between plastic films of various compositions.Those films assembled in a sandwich confi-guration, are then either wound around a carrier core, with a winding pitch different from the strip width, or stacked onto each other so as to obtain a stacked assembly which may be twisted around its main direction for suppressing the mechanical stresses onto the compressed or stretched external or internal parts of the finally obtained cable when said latter has to be wound In the first method, for obtaining the strip structure, it is required to arrange the individual opti-cal fibers according to a flat ondulated pattern to minimize micro-bends when the obtained cable is finally wound. In addition to the difficulties in the fabrication, such a method necessitates to 1~35~Ç4 utilize optical fibers having a length significantly greater than the length of the final cable to be obtained. The second method, although providing for better connection possibilities of the ob-tained cable, is however confronted to difficulties to be carried out practically.
There are also known in the art cable supporting structures which are complex and difficult to manufacture, wherein a cylindrical central core comprises along its generating lines elongated grooves or slots withi~ which are arranged the optical fibers which are optionally individually coated with a protecting sheath Such a method does not permit to conveniently solve the problems resulting from the brittleness of the fibers with respect to mechanical or thermal stresses and from the difficulties of interconnecting optical fiber cables or cable elements of this type As a ma~er of fact, the main parameters to be taken into consideration for implementing an optical fiber cable or cable element, more particularly for a high density communica-tion links, are the following ones :
- mechanically, the optical fibers presently available show a high ultimate tensile strength but substantially no elongation Therefore, the structure of a cable comprising a plurality of fibers has to be designed in such a way that no signi-ficant mechanical stress, i e. tensile, bending or twisting stress is applied onto the fibers, Moreover, micro-bends and micro-breakages are liable to appear onto fibers submitted to certain types of mecha-nical stress. It is well known that the aforementioned phenomenas result in a very short increase of the attenuation of the optical signals transmitted by the fibers;
- thermally, it is also known that the coating ~135~94 of fibers, which is o~ten recommended for ensuring a mechanical protection ~ereof, is an extremely difficult operation as it submits the fibers to mechanical stretchi~ and twisting stresses and mainly to thermal stresses liable to damage the fibers as concerns its mechanical and light transmission characteristics, In order to avoid those dirliculties, it is accordingly suitable to provide a cable structure allowing this coating operation to be suppressed,whereby preventing the fibers from being submitted to important stresses during coating operation in manufacturing the cable; and - as regards connection of the fibers with one another or with emitting or receiving terminal equipments, it is also known that connection systemsare required depending upon the nature and the size of the optical fibers, which must be very accu-rate and are difficult to make and implement, It is further known that connec~ion of fiber arrays in the form of superimposed sheets or strips is easier than in the form of successive cylindrical layers, In addition to the mechanical and thermal resis-tance of the cable, a special attention should be drawn to its re-sistance to ageing, The nature and the form of the components of the cable which protect the optical fibers received therein must be designed to ensure said protection function during the total safe life of the optical cable, It is accordingly required to select materials which do not suffer substantial degradation in course of time and to take care that the structure of the cabling ~lement does not induce permanent stresses into the constitutive components, BRIEF SUM~RY OF THE I~VENTION

An object of the invention is to provide a novel cabLing element and optical fiber cable significantly solving the above problems.
Another object of the invention is to provide 1135~394 a new cabling element ~or optical fibers which is easy and cheap to manufacture, ~hich permits to manufacture unitary cabling ele-ments or high ~ensity fiber cables while considerably minimizing the mechanical stresses into the fibers.
yet another object of the invention is to pro-vide a novel unitary cabling element or optical fiber cable having a reduced size for a given number of fibers A further object of the invention is to provide an improved unitary cabling element which is designed to substan-lo tially lower the effects of the permanent inner stresses due to the deformation of the c~ing element after the optical fibers have been disposed within the recesses, e.g, after it has been helically wound with an important pitch around a central carrier element The invention provides for a cabling element for optical fibers comprising an elongated strip member of a generally slender configuration, formed essentially of a flexible plastic material, and having a substantially continuous first or outer face, first and second side edges~and a second or inner opposite face, a series of longitudinally extending parallel recesses arranged in spaced relationship along a transversal direction of the strip member, each opening into said second face by an access channel, two adjacent channels defining therebetween a longitudinal-; ly extending rib member, the opposite side faces of each channel being conformed so as to come into mutual contact engagement when said strip member is wound around a longitudinal axis or core member so as to have said first and second side edges mutually contacting, whereby realizing a flexible hollow tu~ular structure with a series of angularly spaced closed recesses arranged subs-tantially along a circu7ar pattern The invention also provides for a -unitary cable 1135~

element ~or optical ~ibers obtained from such cabling element which is wound around an elongated cylindrical carrier member or core having a high tensile resistance, an optical fiber being loo-sely arranged within at least some of said recesses According to the inven~ion, the methoa for manufacturing such a cable ~ement comprises the ste~s of extru-ding the recessed strip member, cooling and drying said strip member, opening said recesses and inserting therein optical fibers, closing said recesses by transversely distorting said strip member -to bring same into a closed cylindrical configuration,and helically twisting said strip member with said optical fibers therein around an elongated carried member.
According to another aspect of the invention, for connection of the thus obtained cable element, there is provided an end-piece co~prising a body which presents a first tubular end portion adapted to be fastened to one end of such a cable element, and a second end portion having a substantially rectangular cross-section, the inner chamber of said body having, at least at the level of said second end portion, a flat inner wall onto which is lying the outer face of the flattened unwound end portion of saia cable elemsnt, said strip member end being maintained in a substan-tially flat configuration within said chamber by web members exten-ding transversally through said chamber within said body.
The present invention thus psrmits to combine the advantages of the cylindrical cable structures, more particular-ly as concexns utilization of convential equip~ent in cable manufac-turing, and those of the strip or sheet structure cables, more particu~ rly as concerns easy insertion o~ the fibsrs and, as above mentioned, the limitation o,~ the mechanical stresses, as also the 3~ liability to connection or interconnection of said cables, while 1~35~94 suppressing most of the drawbacks inherent to said different cable structures p~r se.
According to another feature of the inwention, the cabling element, in its rest or initial condition, has at least a partially cylindrical shape, the longitudinal symmetry planes or the channels and associated recesses concurring substan-tially at the level of the longitudinal main axis of the cylindri- -cal element With such an arrangement, when the recessed strip member containing the optical fibers is wound around the central carrier member, the material of the strip member is no more subject to stresses resulting from a ~orced orientation of the molecular chains in the plastic material of the cabling element, Accordingly, in the assembled condition, e g~ the cabling element being wound around the carrier member, there is no substantially static fatigue created inside the material, whereby detrimental affects onto its plastic phase are suppressed.

BRIEF DESCRIPTIO~ OF THE DRAWINGS

The invention will be more clearly understood by reference to the following description of certain preferred embodiments o`f the invention taken in connection with the accom-panying drawings, in which :
- Figure 1 is a cross-sectional view of a first embodiment of the cabling element in the form of a recessed strip member according to the inventi.on;
- Figure 2 is a cross-sectional view of a uni-tary cabling member obtained by winding the strip member of Figures 1, 9 and 11;
- Figure 3 schematically illustrates the steps of the method for fabricating the strip member of the invention;

~13S6394 - Figure 4 schematically shows an apparatus for manufactuing the cable member of Figure 2 from a cabling element according to the invention;
- Figure 5 is a longitudinal sectional view of an embodiment of the conforming and winding or closing dye for winding the cabling element with the optical fibers received the-rein, - Figure 6 is a longitudinal sectional view of an end fitting for a cable element according to the invention;
- Figure 7 is a cross-sectional view of an optical fiber cable embodying cable elements as shown in Figure 2;
- Figure 8 is a cross-sectional view of another embodiment of an optical fiber cable obtained from cabling elements according to Figure l;
- Figures 9 to 12 are cross-sectional views of other embodiments of a cabling element according to the invention;
- Figures 13 ana 14 are respectively a top view and a side view of an embodiment of an apparatus for inserting the optical fibers into the cabling element of Figures 9 to 12 and for closing same; and - Figure 15 schematically shows a plant for manu-facturing a cable member according to the invention, DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to.Figure l., a:cabling element according to the invention has the form of a generally flat strip member 1 comprising a continuous flat first or bottom face 2 and a series of longitudinally extending recesses 3 arranged in spaced parallell relationship along the transversal direction of the strip member for receiving each an optical fiber 4. The recesses or - 30 chambers 3 have a cross-section which is great with respect to the , 11350~4 section of the optical fibers 4, whereby said latter may be loosely received within said recesses ~he recesses may have any convenient shape in cross-section, but preferably have an elliptical or cylindrical configuration, the diameter of said recesses being 5comprised between about 5 and lO times the diameter of the fibers.
Each recess 3 opens into the upper face o~ the strip member opposite to the bottom face Z by an access channel 5, two adjacent channels defining therebetween a longitudinally extending rib-member 6, the end or outer faces of said rib member lOextending substantially within a plane parallel to the plane of the bottom face 2. In the rest condition of the strip member, ?
each channel 5 has a generally trapezoidal shape, the facing side faces 7 of each channel diverging outwardly under an included angle ~of about 360/n, n being the number of longitudinal recesses 15of the strip member. Similarly, the strip member l has a substantial-ly trapezo~dal configuration in cross-section, with the opposite first and second side edges 8 and 8' converging upwardly from the bottom face 2. With such a configuration, it is thus possible to wind the strip member l around a longitudinal axis to cause the 20side edges 8 and 8' to come into mutual contact, thereby realizing a hollow tukular structure as sh~wn in Figure 2. when distorting, e.g winding ~he strip member to have the final configuration in Figure 2, the facing side faces 7 of the channel 5 come into pressure contact against the other, whereby sealingly closing 25the recesses 3, as illustrated in Figure 2. The sid~ edges 8 and 8' of the strip member are advantageously each provided with com-plementary engaging means, for instance of the tenon and mortise joint or of the groove and tab joint type as illustrated at 9 and g' in Figures l, 2, 9, lO and 11.
More specifically, after the optical fibers 4 1~35094 have been deposited within the recesses 3 through the access channels 5, the strip member 1 is helically wound around an elongated central cylindrical carrier or core member 10 and is maintained in its closed tu~ular configuration around said core member by mutual engagement and bonding of the contacting side edges 8 and 8' and by a surrounding, e g ribboned, sheath 11 To yet improve the sealing of the thus obtained closed struc- -ture, the mating faces 7 of the channels may be prealably coated with an adhesive In order to achieve a close fitting of the lo wound strip member onto the central carri.er core 10, the external faces 12 of the rib members 6 are advantageously shaped according to a portion of a cylinder having a radius co~esponding substan-tially to the radius of the central carrier 10 The strip member 1 is advantageously made of polyoléfine or of cellular or solid polyamide by an extrusion pro-cess, the central carrier 10 being made of a material having a high tensile strength, for instance the material available commercially as "Kevlar", or any other similar material showing the required properties of flexibility and tensile stren~th As illustrated in Figures 1 and 2, the strip member 1 preferably includes elon-gated reinforcing members 13 and 13' embedded within the material of the strip member, which further contribute to facilitate extru-sion and handling of the strip members. The reinforcing members 13 and 13' may be in the form of metallic wi~es, of fibers of the . ~C~ ~ale~
25 ~ ~material llKevlarll~ or glass-fibers. In a practical b-ut non limi-tative embodiment, the strip member of the invention has a width determined for manufacturing unitary cable elements having an outer diameter comprised between 7 and 70 mm, more particularly between 10 and 20 mm. For a strip width comprised between about 15 and 20 mm, the distance between the longitudinal axes of the - _ 9 _ ~135C~94 adjacent recesses 3 is chosen between 2 and 2,5 mm.
As illustrated in Figure 2, the recesses 3 are advantageously filled during the fabrication of the unitary cable member 20 with a material 14 which may be either an indicia adapta-ting li~uid or a material for ensuring longitudinal sealing of thecable, for instance a silicone oil,as well known in the manufacture of optical fiber cables. Additionally, as also illustrated in Figure 2, at least some of said recesses 3 may contain in lieu of an optical fiber a metallic conductor 15, in the form of a single lo wire, of pairs or of quarts, coated with an insulating material and provided for feeding repeaters along the transmission line or for forwarding different electrical signals while further assisting the reinforcing members 13, 13' There areshown in Figures 3 and 4 two separate units for carrying out the method of manufacturing a cable element from a strip member of the invention. The plant comprises two separate units, namely the strip member fabricating unit shown in Figure 3, and the optical fiber depos~ing and cabling unit properly shown in Figure ~, the separation between said two units allowing to minimize incidence due to the breaking of a fiber and to carry out easily ~he changing of the fiber carrying spools and the bonding or the welding of the cable elements, In the strip member manufacturing unit schema-tically illustrated in Figure 3, the tensile reinforcing members 13 unreeled from a reel-16 are introduced within an~extrusion head 17 for extruding the constitutive material of the strip member 1, for instance a polyolefine, the extruded ~ction or strip member 1 with the reinforcing members embedded therein being afterwards cooled within a tank 18 and dried at a drying station 19, preferably by means of heated air streams, the thus ~135~94 cooled and dried strip member being received and wound onto an intermediary storing reel 30, In the ca~ling unit shown in Figure 4, the strip member 1 is unwound from said storing reel 30 to be for warded towards a deposi~ing station 21 wherein the optical fibers 4, unreeled from storing ree~s 22, are introduced within the recesses 3 of the strip member. Before reaching the depositing s.ation 21, the strip member 1 is displaced past a station 23 wherein it is pre-heated, for instance by means of heated air streams, and/or stretched in order to prevent ulterior shrinXing and corresponding stresses into the fibers, At the depositing station, the strip member 1 passes over a convex roll 24 with;
its bottom face contac,ting the roll which causes the strip member to be distorted tranversally, e,g, opened, whereby the channels 5 are spread apart and give free access to the recesses 3. The optical fibers 4 are thus deposited into said recesses, either by means of air streams or through capillar tubes, as schematically illustrated at 25 in Figure 4, ~he strip member 1 with the fibers received within the recesses 3 then passes over a concave roll 26 which realizes a counter-deformation of the strip member in the - transversal direction7 whereby reducing the width of the channels 5, ~he thus partially prewound strip member is wound and closed around the central carrier 10 .previously coated with a convenient adhesive within a winding or closing die apparatus 27 illustrated in details in Figure 5, At the outlet of the closing apparatus 27, the unitary cable element 20 receives a sheathing consisting of helically w~und ribbons 28, 28' before being finally wound around a storing drum 31. As illustrated by the arrows 29 and 29', the central carrier 10, as also its feeding drum 32 and its receiving drum 31, are caused to rotate around the longitudinal axis of the 113~g4 central carrier 10 in order to impart , as above mentioned, to the unitary cable element 20 a helical torsion having a pitch far greater than the diameter of the optical fibers. Typica the twisting pitch is determined so as a reference generating line of the unitary cable element, for instance the junction line between the contacting side edges 8 and 8', is rotated of 360 over a cable length of about 4 meters.
As shown in Figure 5, the die of the winding and closing apparatus 27 presents internally a generally converging la shape with a bearing wall 33 which is initially flat at the entry of the die and which continuously merges into the tubular outlet 34 of the die, whereby the strip member 1 bearing against said wall 33 by its bottom face 2, has its side edges progressi-vely raised upwardly, as illustrated at the middle of Figure 5, and closed up to come into mutual contact at the outlet 3~ of the die There is shown in Figure 6 an end fitting for the unitary cable element 20 which is arranged so as to present the different constitutive different fibers in the cable in a substantially flat or strip configuration, in order to facilitate, as above mentioned, connnection of the fibers with another fibers or with an emitting or receiving equipment One can recognize in Figure 6 the end of the unitary cable member 20 with its ribboned sheath 28 and its central carrier .25 10 The end fitting, generally designated by reference numeral 35, has the form of an hollow body comprising a lower half 36 and an upper half 37 interconnected by clamps 38 which also serve -. to fasten the cable end 20 within the fitting 35. Halves 36 and 37 mutually define an inner chamber 39, the cross-section of which progressively varies from a first or upstream cylindrical ,, 113S~

end ~o towar~s a second or downstream quadrangu]ar opposite end, for instance rectanyular As illustrated in Figure 6, contrarily to the windin~ step disclosed in reference with Figure 5, the end portion of the cylindrical cable element 20 is unwound downstream the intermediate portion clamped withint the cylindrical end portion ~0 of the fitting to have the erd portion of the strip member 1 brought back to a flat configuration with its outer or bottom face 2 lying onto the inner flat wall ~1 of the fitting 35. The strip member 1 is maintained lying-on flat on the inner face 41 of the fitting with the optical fibers 4 arranged in a flat array by means of web members 42 integral with the upper half 37, which extend transversally throughout the inner chamber 39. The fitting illus~rated in Figure 6, which permits the conversion of the unitary cylindrical cable element into a substantially flat or planar structure, thereby facilitating the access to each fiber for measurement or connection purposes, is given by way of example and may be extrapoled for interconnection of two cable members, such a fitting being eventually provided with a connection means for connection to different transmission equipments or with a fastening means for fixation to such a connection equipment.
In the passive fitting arrangement, illustrated in Figure 6, the second half 37 comprises an end wall 43 normally closing the inner chamber 39~whereby protecting the stripped fiber ends a therein.Said end wall 43 is for example connected to the body of the upper half through a breakable junction ~4, whereby said end wall may be easily separated from the fitting to five access to the fibers 4 for measurement or connection purposes Figures 7 and 8 show two embodiments of a high density cable embodying unitary elements of the type illustrated il35~94 in Figure 2 as obtained from strip members of Figures 1 and 9-12, In the cable illustrated in Figure 7, an array of six unitary cable elements 20 is angularly spaced around a central unitary cable element 20; said bundle of unitary cable elements 20, which is eventually twisted, is surrounded by a sheath of thermo-plastic material 45, for example of a polyethylene, which may be associated to an inner sheathing or metallic barrier 46, for example out of aluminum, The outer sheath may also include tensile reinforcing elements and/or being internally provided with means for mechanical protection of the cable and/or for preventing entry of moisture within the ~able according to technics fairly known in the art of electric cables; a filling material or wad-ding ~5, for instance out of polyethylene, fills the spaces between the unitary cable member inside the sheath. Such a cable may comprise between 70 and 80 fibers with an outer diameter lower than 25 mm.
In the embodiment shown in Figure 8, a second unitary cable element 20 is concentrically wound around a unitary cable element 20 analogue to that shown in Figure 2, said latter acting, with respect to the second unitary cable element 20t, as a central carrier similar to the carrier core 10 for the inner or first unitary cable element 20. The cable of Figure 8 is also terminated by being surrounded with sheathes 45 and 46.
With the cables of Figures 7 and 8, each unitary cable element thereof may be partially unwound at its end portion with the strip member brought back to a flat configuration for equipment with an end fitting such as that illustrated in Figure 6.
In the embodiment illustrated in Figure 9, the unitary cabling element 100 has at least a partially cylindrical 11354~94 shape, the inner faces 12 of the ribs 6 between two adjacent channels 5 defining a first inner cylinder having a radius Ro, the outer continuous face 2' of the cabling element being also cylindrical and extending parallel to said first cylindrical surface having a radius Ro. Similarly, in the rest condition o~
the cabling element shown in the drawings, the different recesses 3, 3~ are angularly spaced on a circle having a radius Rl centered at the common axis 0 of both inner and outer cylindrical surfaces of the stxip member.
lo In the embodiment of Figure 9, the unitary cabling element extends over an included angle of about 90, the planes of the opposite lateral faces on side edges 8, 8' concurring at the level of the axis 0. In the embodiment illustrated in Figure 11, the cabling element has an aperture of about 1~30, In the different configurations, according to a feature of the invention, the channels5 and the associated recesses 3 each havea common longitudinal symmetry plane, the longitudinal symmetry planes lol of the different channels and associated recesses all con-curring substantially at the level of the axis 0 of both inner and outer cylindrical surfaces of the cabling element~
As illustrated in the drawings, each cabling element loo comprises at least a reinforcing member 13, 13' having a high tensile strength embedded within the plastic material constitutive of the cabling element when extruding same. Said constitutive material is, as for the embodiment in.Figure 1, a polyolefine or a polymer,typically polyethylene, In the embodiment illustrated in Figure lo, wherein the cabling element has an aperture greater than 90, in order to increase transverse elasticity of the strip member, the outer surface 2' is formed with successive longitudinal ~135l~394 corrugations, the ape~es or top portions thereof 201 being subs-tantially in alignment with the longitudinal symmetry planes of the paired channel-recesses, the intermediate recessed or bottom portions thereof laying substantially at the level of the radial planes extending intermediary between two such longitudinal sym-metry planes, so as, adjacent said latter, the thickness e of the wall portion surrounding externally the recesses 3 be subs-tantially constant~ With such an arrangement, closure or winding of the cabling element is facilitated while the stresses created therein during the preliminary opening or flattening step of the cabling member-are reduced. As in the embodiment in Figure 1, the recesses 3 have typically a circular cross-section, but they may alternatively have a substantially oval or ovoid cross-section as illustrated on the right portion of the cabling element in Figure 9, or any convenient shape.
There is illustrated in Figure 12 an embodiment of a unitary cabling element 20 of the invention which has initially, e,g in its rest condition, an entirely cylindrical configuration which accordingly exactly corresponds to the ~inal shape of the final unitary cable element when the cabling element has been arranged around the inner carrier member, with the exception that the facing side edges 8 and 4', although adjacent one to each other, are not secured one to each other in said initial condi-tion, said side edges being mutually secured only after the cabling element has been opened to arrange the optical.fibers 4 in the recesses, and caused to rel~ase so as to automatically recover its initial configuration around the central carrier member 10 In said embodiments, the strip member 20 is extruded in its cylindrical configuration, the longitudinal radially extending slit defining the facing adjacent side edges 8, 8' being ~135~9~
formed either when extruding the strip member, or ul-teriorly, by cu~ting, for instance just be~ore the step of opening or distortin~3 the strip member to bring same to a substantially ~l~tened configuration. Said cylindrical strip member is subject to inner stresses only during the opening of the strip member to arrange there~ the optical fibers and the central carrier member 10, said momentary stresses never going beyond the yield strength of the plastic material of the strip member. It results therefrom that the final unitary cable element including the optical fibers is free from any inner stress and has accordingly a considerably increased service life.
Although at least in the embodimentsillustrated in Figures 9 to 11, the mating faces 7 of the access channels 7 to the recesses are normally separated one from each other as in the embodiment of Figure 1, so as to come into mutual contact engagement only when the cabling element is completely closed or wound around a longitudinal axis, e g inner core, in order to facilitate insertion of the optical fibers and of the electric conductors into the recesses 3, more particularly if the included angle of aperture of the cabling elementis comprised between 180 and 360 such as illustrated in Figure 12, use is made, upstream the winding device 27 analogue to that disclosed in relation with Figure 5, of an opening or speading device 210 to cause the cabling element 100 to be distorted towards a flattened configuration whe-rein it is less bent that its normal rest o~nfiguration As a nonlimitative embodiment, the opening device 210 illustrated in Figures 13 and 1~, comprises a roll 211 extending transversally to the normal run direction of the strip member loo which is forwarded up to said roll according to an important angle in order to widely spread apart the strip member as best seen in Figure 13, -- . . . . ..

113~394 whereby the matin~ faces 7 of the different channels 5 are su~ficiently separated one from each other lnthe vicinityofthe contact generati~ of the roll at the level of which is carried on insertion of the optica] fibers 4, the strip member being ulteriorly authorized to recover its at least partially cylindri-cal or bent configuration a~und the central carrier member 10, said bending being completed so as to achieve a complete winding of the strip member in a winding or closing apparatus 27 analogue to that illustrated in Figure 5, The fabrication plant fo.r manufacturing the unitary cable element 20 may be divided into two separate produc.
tion lines as disclosed with reference to Figures 3 and 4, but may also consist in a single continuous line as illustrated in Figure 15, In Figure 15, after leaving the drying station 19, the cooled and dried strip member 100 is directly directed toward the opening and winding station 270 illustrated in Figures 13 and 14 while being simultaneously advantageously pre-stretched, When leaving the winding and opening station 270, the unitary cable member 20 is surrounded by a sheathing consisting of helically wound ribbons 28, 28', the central carrier 10 being simultaneously caused to rotate around its longitudinal axis to impart to th~
unitary cable member 20 helical twisting having a pitch far greater than the diameter of the fibers ~efore the cable element is finally wound aroun~ the storing drum 31.
Although the foregoing description presents preferred embodiments of the invention, modifications and changes may appear to those skilled in the art, which will come within the scope and spirit of the appended claims,

Claims (26)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1 - A cabling element for optical fibers, which comprises an elongated body in the form of a strip member made of a flexible plastic material, said strip member having a first conti-nuous face, a second opposite face, first and second side edges, a series of longitudinally extending recesses arranged in spaced parallel relationship, each said recess opening into said second face of said strip member by an access channel, two adjacent chan-nels defining therebetween a longitudinally extending rib member, the mating faces of each channel being shaped so as to come into mutual contact engagement as a result of the winding of said strip member around a longitudinal axis to cause said first and second side edges to be brought into mutual contact engagement, whereby realizing a hollow tubular structure with a series of inner closed recesses angularly spaced according to a substantially circular configuration

2 - A cabling element according to claim 1, wherein said recesses have a cross-section substantially greater than that of said optical fibers

3 - A cabling element according to claim 2, wherein each said longitudinally extending rib member has an outer face which is shaped to conform to a portion of a cylinder having a radius corresponding to the inner radius of said hollow tubular structure to be finally obtained.

4 - A cabling element according to claim 3, wherein said strip member is formed of an extruded polymer-composition

5 - A cabling element according to claim 1, wherein said strip member comprises at least one elongated reinforcing mem-ber embedded therein.

6 - A cabling element according to claim 1, whe-rein said strip member has a generally flat configuration, said channels having, when said strip member in its flat configuration, a substantially trapezoidal shape, said mating side faces of each channel diverging outwardly with an included angle .alpha. of about 360°/n, n being the number of the recesses of the strip member.

7 - A cabling element according to claim 1, wherein said strip member has, in a rest condition, at least a partially cylindrical configuration having a common longitudinal axis, said channels and the associated said recesses having radial symme-try planes concurring substantially at the level of said longitu-dinal axis of the cylindrical cabling element

8 - A cabling element according to claim 7, wherein the included aperture angle of the cylindrical cabling element is not less than 90°.

9 - A cabling element according to claim 8, wherein the included aperture angle of the cylindrical cabling element is comprised between about 180° and 360°.

10 - A cabling element according to claim 7, wherein said recesses are angularly spaced substantially along a circle centered at said longitudinal axis.

11 - A cabling element according to claim 10, wherein said first continuous face is formed with longitudinally extending ondulations, the top portions of which substantially coincide with said differet longitudinal symmetry planes of said associated channels and recesses.

12 - A cabling element according to claim 7, wherein said recesses have a substantially oval cross-section.

13 - A unitary optical fiber cable element in-cluding a cabling element, which comprises an elongated body in the form of a strip member, made of a flexible plastic material, said strip member having a first continuous face, a second oppo-site face, first and second side edges, a series of longitudinally extending separate recesses arranged in spaced parallel relation-ship, each said recess opening into said second face of said strip member by an access channel, two adjacent channels defining there-between a longitudinally extending rib member, the mating faces of each channel being shaped so as to come into mutual contact enga-gement as a result of the winding of said strip member around a longitudinal axis to cause said first and second side edges to come into mutual contact engagement, whereby realizing a hollow tubular structure with a series of inner closed recesses angularly spaced according to a substantially circular configuration, said strip member being wound around an elongated cylindrical carrier element having a high tensile strengh with said first and second side edges in mutual contact engagement while being twisted around the axis of said cylindrical carrier element at a pitch which is great with respect to the diameter of the fibers, at least some of said recesses each containing an optical fiber loosely received therein,

14 - A unitary cable element according to claim 13, wherein said first and second side edges of said strip member are sealingly maintained in mutual contact engagement,

15 - A unitary cable element according to claim 14, wherein said first and second side edges of said strip member comprise complementary engaging means.

16 - A unitary cable element according to claim 13, wherein said recesses containing an optical fiber are filled with an indicia adaptating liquid.

17 - A unitary cable element according to claim 13, wherein said recesses are filled with a material for longitu-dinally sealing the cable element

18 - A unitary cable element according to claim 13, further comprising an outer protecting sheath.

19 - A unitary cable element according to claim 13, wherein at least one recess contains an elongated metallic conductor

20 - An optical fiber cable comprising at least two unitary cable elements each including an elongated body in the form of a strip member made of flexible plastic material, said strip member having a first substantially continuous face, a second opposite face, firs' and second side edges, a series of longitudinal-ly extending recesses arranged in a spaced parallel relationship, each said recesses opening into said second face of said strip member by an access channel, two adjacent channels defining there-between a longitudinally extending rib member, the mating faces of each channel being shaped so as to come into mutual contact engage-ment as a result of the winding of said strip member around a longi-tudinal axis to cause said first and second side edges to be brought into mutual contact engagement,whereby realizing a hollow tubular structure with a series of inner closed recesses angularly spaced according to a substantially circular configuration, said strip member being wound around an elongated cylindrical carrier element having a high tensile strengh while being twisted around the axis of said cylindrical carrier element at a pitch which is great with respect to the diameter of the fibers, at least some of said recesses each containing an optical fiber loosely received therein.

21 - An optical fiber cable according to claim 20, which comprises at least three said unitary cable elements angularly spaced around a centralunitary said cable element.

22 - An optical fiber cable according to claim 20, which comprises a centrally arranged said unitary cable element and at least a second said unitary element concentrically wound around said cerntral unitary cable element.

23 - A method of fabricating a unitary cable element according to claim 13, which comprises the following steps :
a) extruding said recessed strip member with lon-gitudinal reinforcing members embedded therein;
b) cooling and drying said extruded strip member;
c) distorting transversally said strip member to cause said channels to open and inserting therein optical fibers;
d) distoring transversally said strip member to substantially close said recesses;
e) twisting helically at a great path said strip member having said optical fibers therein and wound around a carrier element; and f) providing a protecting sheath around the thus wound strip.

24 - The method of claim 23, further comprising between steps b) and c) the intermediary steps of :
- reeling said strip member onto a storing reel, and - unreeling said strip member from said storing reel and pre-heating said strip member.

25 - The method of claim 23, further comprising between steps b) and c) the step of pre-stretching said strip member.

26 - An end fitting for a unitary optical fiber cable element including a cabling element which comprises an elon-gated body in the form of a strip member made of a flexible plas-tic material, said strip member having a first substantially continuous face, a second opposite face, first and second side edges, a series of longitudinally extending recesses arranged in a spaced parallel relationship, each said recess normally com-municating with said second face of said strip member by an access channel, two adjacent channels defining therebetween a longitu-dinally extending rib member, the mating faces of each channel being shaped so as to come into mutual contact engagement as a result of the winding of said strip member around a longitudinal axis to cause said first and second side edges to be brought into mutual contact engagement, whereby realizing a hollow tubular structure with a series of inner closed recesses angularly spaced according to a substantially circular configuration, said strip member being wound around an elongated cylindrical carrier element having a high tensile strenght, at least some of said recesses each containing an optical fiber loosely received therein, said fitting comprising a composite hollow body having a first tubular end portion adapted to be clamped onto the cylindrical end portion of said unitary cable element, and a second end portion of a subs-tantially quadrangular cross-section,defining an inner chamber within said body having a substantially flat inner wall at least adjacent said second end portion onto which said first face of said end portion of the strip member unwound to a flat configuration is caused to lie while being maintained in flat configuration against said flat wall of said fitting by web members integral with said body and ex-tending transversally through said inner chamber.