GB2040063A

GB2040063A - A fibre optic cable and its method of manufacture

Info

Publication number: GB2040063A
Application number: GB7934801A
Authority: GB
Original assignee: CORDONS ET EQUIPEMENTS
Current assignee: CORDONS ET EQUIPEMENTS
Priority date: 1979-01-15
Filing date: 1979-10-08
Publication date: 1980-08-20
Also published as: ES8100840A1; ES485126A0; DE3000674A1; IT8047574A0; FR2446495B1; BE879301A; IT1126886B; NL7907380A; FR2446495A1; JPS5595911A

Abstract

An optic fiber cable 1 is disclosed having a reinforced central core 5 on which are helically wound contiguous supports 8 for optical fibers 17, 18, 19 into at least one continuous annular layer. Each support 8 has grooves 14, 15, 16 for the optical fibers on its outer, convex surface 10. Each support is matingly encased by an elastically deformable jacket 9 which holds the optical fibers in their grooves. By imparting axial torsion on the optical fibers before they are laid in their grooves equal and opposite to the torsion imparted by the supports the resultant axial torsion on the optical fibers is nil. <IMAGE>

Description

SPECIFICATION A fiber optic cable and its method of manufacture The invention relates to fiber optic cables.

In telecommunications signal transmitting light waves travelling in light guides or optical fibers are used increasingly.

These optical fibers, customarily with a glass or silica center, mostly have diameters less than a millimeter which makes them fragile notably with respect to traction and torsion.

It has been proposed to accomodate a plurality of optical fibers in a cable comprising one or more high-strength centers or supports and one or more casings for holding and insulating the fibers.

Afirsttype of cable comprises a cylindrical supporting core with an axial metal center. At the periphery are longitudinal grooves each of which is adapted to freely accomodate an optical fiber. An outer casing bearing against the crests defining the limits of the grooves holds the optical fibers and insulates them from external influences without the optical fibers being in frictional contact with one another. In such a cable the number of optical fibers is relatively small with regard to the cross-sectional area of the cable. In addition different kinds of cores for constructing cables with different numbers of optical fibers must be provided.

According to another proposal the optical fibers are accommodated in grooves in nested support tapes of rectangular section. All the tapes are encased in a sheath of circular cross-section to form a cylindrical cable. Such a cable is relatively bulky.

A fiber optic cable according to the invention is devoid of these drawbacks. Such a cable has a smaller diameter for accommodating the same number of fibers. It is of simple and economical fabrication. It employs standardized parts for cable constructions of different diameters.

Thanks to the reduced diameter of the cable according to the invention, the connectors to which it is connected may also be of smaller dimensions, which is a generally sought-after objective.

According to the invention, there is provided a fiber optic cable comprising a high-strength axial cylindrical support core, longitudinal grooves accommodating optical fibers, and at least one protective casing, characterized by a plurality of juxtaposed optical fiber supports disposed around the central core thereby forming at least one cylindrical layer, each one-layer support being wound helically on the previous layer.

According to a preferred embodiment of the invention, the optical fiber supports form a plurality of concentric layers.

According to the invention, there is also provided a method of fabricating such a cable, comprising continuously forming a cable starting with a cylindrical central core and juxtaposed optical fiber supports wound helically around the core in at least one layer and laying the optical fibers continuously in the supports proximate to the point of formation of the cable.

Advantageously the optical fibers are prior to their being placed in the grooves of the supports subjected to torsion equal and opposite that imparted by the support to the fiber when they become part of the cable, owing to its helical arrangement relative to the axis of the cable.

In the description which follows, of several embodiments, reference is made to the accompanying drawings, in which: Figure lisa cross section of a cable having single optical fiber support layer; Figure 2 is a cross section of a cable having a plurality of optical fiber support layers; and Figure 3 is a diagrammatic perspective view of a setup for manufacturing an optic fiber cable.

In Figure 1, a cable 1 comprises an axial center 2 formed by seven high-strength stranded wires 3 surrounded by a plastics casing to form a cylindrical core 5. At the periphery 6 of the core 5 are five juxtaposed optical fiber accomodating compartments 7,,72,73,74 and 75. Each compartment 7 comprises a fiber support 8 surrounded by a jacket 9.

The fiber support 8, made of flexible plastics material, has a convex surface 10, a concave surface, both of which a cylindrical, substantially coaxial to the outer surface of the cyindrical core 5, and two radial side surfaces 12, 13. Three substantially rectangular longitudinal grooves 14,15 and 16 are formed in the convex surface 10 of the fiber support. Each optical fiber 17, 18, 15 respectively accommodated in one of the grooves 14, 15, 16 with some clearance or play so that the fibers are not subjected to mechanical stress. In the plastics material of the optical fiber support 8 is embedded an armor wire running parallel to the surface 10 and lying in the plane of symmetry of the support 8, which confers high strain resistance to the support 8.

The jacket 9 is formed by a flexible plastics material section of substantially constant wall 21 thickness and curvilinear trapezoidal or trapezium cross section but is not closed, as its inner wall has two free edges defining a gap 22. The jacket 9 is put into place on the support 8 after opening it by plastic deformation and the inner surface 25 of its outer surface snugly embraces the convex surface 10 of the support 8 so that this surface seak off grooves 14, 15 and 16 to enclose optical fibers 17,18 and 19 while the outer surface 26" 262 of the inner wall bears against the periphery 6 of the core 5. The compartments 7 including their jackets 9 are wound contiguously helically around the core 5 along the entire surface thereof at a predetermined pitch.

Along the periphery 27 of the five jackets of the compartments 7 juxtaposed around the core 8 is wound an insulating tape 28 which acts as a support for an outer cylindrical sheath 28 of the cable.

The cable with a plurality of layers of fiber accommodating compartments is represented in Figure 2 comprising a central core 30 similar to the core described in the preceding embodiment. The core is surrounded by four superposed cylindrical layers 31,32,33 and 34, each layer being comprised of a plurality of optical supporting or fiber guiding compartments similar to those of the previous embodiment. The layer 31 is formed of five contiguous compartments, layer 32 of eight compart ments, layer 33 of eleven compartments and layer 34 of thirteen compartments. These numerical indications as well as the previous numerical examples are given by way of non limiting examples. On the last layer 34 are placed a tape 35 and a sheath 36.

The fiber guide supports and the surrounding jackets are flexible and they adapt themselves to the radius of curvature of the periphery of the preceding layer on which they are placed so that the same fiber guide supports and jackets may be used for various layers of the cable.

The cable represented in Figure 2 comprises thirty-seven similar compartments, each carrying three optical fibers, therefore the number of fibers carried by the cable is one hundred eleven.

To manufacture a cable according to the invention a set-up as shown in Figure 3 is used, comprising a reel unwinder (not shown) carrying a reel 50 on which is wound a cylindrical drum receiving stranded wire for forming the core 51 of the fiber optic cable.

The set-up also comprises a reel winder, not shown, adapted to support a reel 52 for winding cable on a shaft 57 parallel to the axis of the reel 50.

The core 51 provided with a plurality of compartments for accommodating optical fibers along its periphery and a protective tape as will be described hereinafter, is wound on the cable take-up reel 52 by a winder, not shown. The core 51 is displaced at constant speed from reel 50 to reel 52 suitably tensioned along line 53 which passes through the centers of symmetry 54 and 55 of the respective reels 50 and 52.

In addition to their rotational movement about axes 56 and 57 reels 50 and 52 with fixed centers 54 and 55 of symmetry, each of the reels is rotated about the straight line or axis of rotation 53. The rotation of the reels 50 and 52 about axis 53 is at the same speed and in the same direction so that the axis 56 of rotation of reel 50 and axis of rotation 57 of reel 52 remain parallel. The core 51 unwound from the reel 50 and wound on reel 52 subsequently being covered is subjected to rotational movement, indicated by arrow 58, about its own axis over the straight-line path 59 from reel 50 to reel 52.

On the core 51 are arranged helically juxtaposed optical fiber compartments for forming a first layer, if desired, a second layer composed of compartments is placed supported on the first layer and so on until the desired number of layers is obtained.

In Figure 3 is represented the positioning of an optical fiber compartment, other compartments 61, 62, 63 and 64 being merely schematically represented by phantom lines, the mode of positioning on the core 51 to form a layer of five optical fiber compartments being similar to what is going to be described in respect to compartment 60.

The optical fiber accommodating compartment 60 comprises a grooved support 61 in which are place three optical fibers 62, 63 and 64 and a jacket 65 placed around the support accommodating its fibers.

At the outset of manufacture of the cable the ends of the fiber accommodating compartments 60 are fixed to the end of the core 51 before fastening the same to the empty reel 52.

The support 61 is fed by a reel 66 carried on a fixed spindle 67 on which it rotates preferably with slight friction contact. The jacket 65 is fed from a reel 65 mounted on a fixed spindle 69 parallel to spindle 67 and preferably with light friction. The support 61 is covered with the jacket 65 at a point 70 remote from reel 66. The positioning of the jacket on the support is carried out with elastic deformation of the jacket which permits it to embrace the support. On its path between the reel 66 and point 70 the support 61 is devoid of any jacket. In each of the three grooves present in support 61 is an optical fiber 62, 63, 64 coming from a fiber supply reel 71,72,73 respectively.The optical fibers are advantageously disposed in the grooves by means of hollow guide needles with the ends disposed substantially tangent to the bottom wall of their respective grooves. Each optical fiber emanating from a reel 71,72,73 passes through the internal channel of the needle which guides it into a groove. The end of each fiber is initially fixed to the end of the support 61.

The optical fiber supply reels 71,72 and 73 are idly mounted on parallel spindles 74,75 and 76 respectively. The assembly formed by these three reels may be controlled for rotational movement indicated by arrow 77 about a spindle 78 lying in the plane of spindles 74,75 and 76 and perpendicular thereto.

The rotational speed of the assembly is adjustable.

The set-up operates as follows: Optical fibers 62, 63 and 64 passed through their respective guide needles are fixed by any appropriate means to the end of the support 61. The support is provided with a jacket 65 along a predetermined length thereby permitting the fixing of the compartment 60 so provided at the end of the core 51 as described above. The procedure is the same for the other compartments laid with fibers.

The set-up is started. The core 51 then undergoes translatory and rotational movement about itself so that the compartment 60 winds itself helically around the core 51, the inner surface 26a,262 of the compartment 60 being in continuous contact with the core 51 at a point 80. The five compartments 60, 61, 62, 63 and 64 are thus helically juxtaposed on the core and define a layer of connective, contiguous turns on which is placed another layer of other compartments for optical fibers prepared by other set-up for supplying fibers into supports and placing jackets therearound, as described.

When the desired number of layers has been positioned, a protective tape 81 from a reel 82 is wound around the thus formed cable before it is wound on the reel 52. When reel 52 is full it is transported to a sheathing set-up which covers the cable with a sheath of plastics material.

Owing to the helical arrangement of the optical fiber compartments around the core 51 the optical fibers therein are subjected to axial torsion the magnitude of which is equal to the winding pitch of the compartments around the core. This torsion may damage the optical fibers and it is desirable to eliminate it.

To this end, the invention provides that the assembly 100 carrying reels 71,72 and 73 for supplying optical fibers is rotated about the spindle 78. This rotation the speed of which is related to the laying speed of the optical fibers in the grooves of the support 61, imparts an axial torsional force to each such fiber. The invention provides that the torsional force is equal to and opposite that which is imparted to the fibers by the support when it is in its ultimate position in a helix on the fnished cable. In this way the two torsional forces cancel each other out and the optical fibers of the cable are not subjected to axial torsion caused by helical arrangement of their supports.

Claims

1. A fiber optical cable comprising a reinforced cylindrical central core, optical fibers being arranged in longitudinal grooves, and an outer protective sheats, characterised in that the grooves are defined in supports of part annular cross-section helically wound around the core.

2. A cable as claimed in claim 1, characterised by the supports being disposed side by side, forming a continuous layer around the core.

3. A cable as claimed in claim 2, characterised in that there are a plurality of superposed layers of supports.

4. A cable as claimed in any one of claims 1,2 or 3, characterised in that each grooved support is provided with a jacket for holding the optical fibers in their respective grooves, the jackets being of open contour shaped to elastically deformably embrace their associated supports.

5. A support for optical fibers as claimed in any one of the preceding claims, characterised in that its section is a cylindrical sector with substantially radial sides and its longitudinal grooves in its convex surface.

6. A support as claimed in claim 5, characterised in that the support is made of flexible plastics material, longitudinal armor wires being embedded in the support.

7. A support as claimed in claim 5 or 6, characterised in that the support is provided with a jacket of flexible plastics material having a constant wall thickness and an open, curved trapezium crosssection with one side having free edges defining a gap, the free interior configuration of the jacket being adapted to mate with the outer surface of the support.

8. A method of making a fiber optic cable as claimed in any one of claims 1 to 4, characterised in that a plurality of juxtaposed optical fiber supports are helically wound round the right cylindrical core to form layers, the layers being superposed, the supports being continuously fitted with optical fibers proximate to the point where the supports are helically wound on the core.

9. A method as claimed in claim 8, characterised in that each optical fiber support is supplied by a first reel and is provided with an elastically deformable jacket supplied by a second reel the axis of which is substantially parallel to the axis of the first reel, the optical fibers being laid in the grooves of the associated support along the path ofthe said support between the first reel and the place where the jacket coming from the second reel is received on the said support.

10. A method as claimed in claim 9, characterised in that the optical fibers are laid in the grooves of the supports by hollow guide needles with their ends substantially tangent to bottoms of the grooves.

11. A method as claimed in any one of claims 8-10, characterised in that the optical fibers are supplied by reels with parallel axes forming an unit.

12. A method as claimed in claim 11, characterised by rotating the unit carrying the reels of optical fibers so as to impart an axial torsion to the optical fibers before they are laid in the grooves of their support.

13. A method as claimed in claim 12, characterised in that the axial torsion imparted to the fibers is equal to and opposite that which is imparted to the optical fibers by their supports when they are helically wound round the core.

14. A method as claimed in claim 12 or 13, characterised in that the speed of rotation of the unit is controlled as a function of the speed of manufacture of the cable so that the resultant axial torsion imparted to the optical fibers is nil.

15. A fiber optic cable substantially as herein described and illustrated in Figure 1 or Figure 2, of the accompanying drawings.

16. A method of making a fiber optic cable substantially as herein described and illustrated in Figure 3, or as modified by Figure 1 or Figure 2, of the accompanying drawings.