GB2182167A - Optical fibre cable containing undulating optical fibre ribbons - Google Patents

Abstract

An optical fibre ribbon cable 7 has at least one pair of optical fibre ribbons 3 loosely accommodated within a longitudinal channel 6 in the cable sheath 4, the ribbons 3 each following an undulating path and being intermittently connected together at respective peaks and troughs either directly, or indirectly via an intermediate elongate element 10. <IMAGE>

Description

SPECIFICATION Optical fibre cable This invention relates to optical fibre cables ofthe type in which a plurality of optical fibres are loosely accommodated in a longitudinal channel in an outer sheath.

Optical fibre cables have been produced or proposed in various constructions with a view to providing a reinforced sheath, with a high tensile strength, which protects the optical fibres against mechanical stresses, the fibres being free to move within thereby spective channels.

The prior art encounters the difficulty that loose bundles of optical fibres are difficultto connect together, and forthis reason it has been proposed to secure a plurality offibres side by side in the form ofa ribbon.

One approach of the prior art isto wind one or more such optical fibre ribbons around along- itudinal strength member. This enablesthefibresto be easily connected but allows the transference of mechanical stresses to the fibres which can produce micro-bends and micro-breakages in the fibres.

It is an object ofthe present invention to overcome the aforementioned disadvantages to produce an op ticalfibrecablewhich is easilyconnectableand in which the mechanical stresses transferred to the fibres are negligible.

The invention is particularly concerned with an optical fibre ribbon of the kind comprising a plurality of optical fibres arranged side by side which maybe embedded in an elongate body of plastics material.

According to the present invention, an optical fibre ribbon cable comprises at least one pair of optical fibre ribbons, loosely accommodated inside along- itudinal channel within a cable sheath,the ribbons having undulating paths of the same pitch length but oppositely phased, and being intermittently connected where peaks and troughs of the respective ribbons meet.

Such a construction allows the fibre ribbon assembly to stretch to some degree when a tensile load is applied to the sheath, thereby preventing ten sile stresses being imparted to the fibres.

The cable sheath may incorporate strength mem bers in any known manner, but preferably consists of either reinforcing rods (either metallic or non metallic) embedded within the material of the cable sheath or of a reinforcing layer adjacent the inside surface of the cable sheath.

The undulating optical fibre ribbons may be inter mittently connected directly to each other orto a tape or other elongate element,forexampleashaped rod, disposed between them, connections being made in any convenient manner.

One or more insulated electrical conductors, pre ferablycopper, in single, double or quad form may be included in the cable construction. The conductor or conductors may be separate from the ribbons, although in some cases one or more optical fibres of at least one ribbon may be replaced by one or more conductors.

One or more of said longitudinal channels may incorporate any medium suitable to provide water blocking properties.

Any unfilled channels may afford a low pneumatic resistance cable suitable for use in gas pressurised optical fibre systems.

One specific embodiment of the invention and two modifications thereof will now be more fully described byway of example with reference to the accompanying drawing in which Figures land 2 are a lateral cross section and a longitudinal cross section of part of the optical fibre ribbon cable, and Figures 3 and 4 are longitudinal cross sections of modified forms of the optical fibre ribbon cable.

Referring to Figures 1 and 2, the cable comprises, within a longitudinal channel in an outer sheath 4, a pair of optical fibre assemblies each consisting of a plurality, inthis caseten, optical fibres 1 arranged side by side and embedded in an elongate body of plastics material 2 to form an optical fibre ribbon 3.

The two ribbons 3 have undulating paths of the same pitch length, but of opposite phase, and are intermittently connected togetherwhere the troughs of one ribbon contact the peaks of the other. The cable sheath 4 may have a plurality of metallic and/or nonmetallic reinforcing rods within the sheath 4 as at 5, or alternatively the sheath may have a reinforcing layer (not shown) adjacent its inside surface. The channel 6 within the sheath of the optical fibre ribbon cable7 maycontain anysuitable medium having water blocking properties.

The optical fibre ribbons 3 may be connected ac ross theirwhole width or only part of it, connection being effected either by softening the plastic coatings at the appropriate position and pressing the ribbons together at those positions, or by the use of a separate bonding agent.

Referring to Figure 3 the optical fibre ribbon cable 7 comprises two undulating optical fibre ribbons 3 as in the cable illustrated in Figures 1 and 2, but in this case the ribbons are connected to opposite sides of a flexibletape 9. Thetape 9 may be of anysuitable known form or material and the optical fibre ribbons 3 may be connected to the tape 9, in any arrangement, not necessarily that shown in the diagram, that is to say the peaks and troughs need not in this case coincide.

Figure 4 shows alternative means of producing an undulating optical fibre ribbon cable 7. In this case the two ribbons 3 are intermittently connected to opposite sides of a flexible shaped rod 10 having a plurality of transverse projections 11 spaced along it such as normally to maintain the undulating form of the optical fibre ribbons 3 the projections having suf ficientflexibility to allow movement of the ribbons when the optical fibre ribbon cable 7 is flexed, thereby avoiding damage to the fibres but at the same time being sufficiently resilient to restore the undulating form of the ribbons 3. As will be appreciated avarietyofshapesforthe rod 10 are suitablefor the above purpose.

The tape or rod, where provided, may have a relatively high tensile strength so that it provides an internal strength member and prevents tensile stresses on the cable being imparted to the optical fibre ribbons or alternatively it may be resiliently ex tensible,the undulating shape ofthe ribbons allowing assembly without any tensile stress being applied to the fibres.

Three or more fibre ribbons may be connected to each otherin a similar mannerto thetwo ribbons il- lustrated. For example a third ribbon of undulating form may be connected to one or other of the ribbons ofthe ribbon assembly of Figures 1 and 2, the troughs or peaks of the third ribbon being connected to the peaks or troughs, as appropriate, of there- spective ribbon of the assembly.

Claims (16)

1. An optical fibre ribbon cable comprising at least one pair of optical fibre ribbons, loosely accommodated inside a longitudinal channel within a cable sheath, the ribbons having undulating paths of the same pitch length but oppositely phased, and being intermittently connected where peaks and troughs of the respective ribbons meet.

2. An optical fibre ribbon cable according to Claim 1 wherein the cable sheath incorporates a plurality of strength members.

3. An optical fibre ribbon cable according to Claim 2 wherein the strength members comprise metallic or non-metallic reinforcing rods embedded within the material of the cable sheath.

4. An optical fibre ribbon cable according to Claim 1 wherein a reinforcing layer is located adjacent to the inside surface of the cable sheath.

5. An optical fibre ribbon cable according to any of Claims 1 to 4wherein the optical fibre ribbons are intermittently connected directly to each other.

6. An optical fibre ribbon cable according to any of Claims 1 to 4wherein the optical fibre ribbons are intermittently connected to an elongate element disposed between them.

7. An optical fibre ribbon cable according to Claim 6wherein the elongate element takes the form ofatapeora rod.

8. An optical fibre ribbon cable according to any preceding Claim wherein one or more insulated electrical conductors are included in the cable construction.

9. An optical fibre ribbon cable according to Claim 8 wherein the electrical conductors are in single, double or quad form.

10. An optical fibre ribbon cable according to Claim 9wherein the electrical conductors consistof copper.

11. An optical fibre ribbon cable according to any of Claims 8 to 10 wherein one or more optical fibres of at least one ribbon may be replaced by one or more conductors.

12. An optical fibre ribbon cable according to any of Claims 8 to 1 wherein the conductor or conductors is/are separatefrom the ribbons.

13. An optical fibre ribbon cable according to Claim 1 wherein one or more ofthesaid longitudinal channels incorporates a medium suitable to provide water blocking properties.

14. An optical fibre ribbon cable according to any preceding Claim wherein any unfilled channels afford a low pneumatic resistance cable suitable for use in gas pressurised optical fibre systems.

15. An optical fibre ribbon cablecomprising at least one pair of optical fibre ribbons, loosely ac commodatedwithin a longitudinal channel in a cable sheath, wherein the ribbons are each of undulating form and are located on opposite sides of a flexible elongate element, the element being connected intermittentlyto the ribbons at respective peaks or troughs.

16. An optical fibre ribbon cable substantially as hereinbefore described with reference to Figures 1 and2orFigures3or4oftheaccompanyingdrawing.