GB2123164A

GB2123164A - Optical fibre cables

Info

Publication number: GB2123164A
Application number: GB08216628A
Authority: GB
Inventors: Robert Dewi Edwards; David Delme Jones
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-06-11
Filing date: 1982-06-11
Publication date: 1984-01-25
Also published as: AU559047B2; NZ204427A; GB2123164B; AU1542383A

Abstract

A composite cable construction comprises a longitudinal plastics former (1) having along its length grooves (2) extending parallel to its longitudinal axis. Optical fibre elements (4) are accommodated in the grooves (2) which lie as close to the neutral axis of the former (1) as possible. A strength member (3) of steel or reinforced plastics may be disposed along the central axis. A metallic tape may be wrapped around the former (1), member (3) and the metallic tape serving as the inner and outer conductors respectively of a coaxial cable. At least one of the grooves (2) may contain an electrically conductive cable element. <IMAGE>

Description

SPECIFICATION Optical fibre cables This invention relates to optical fibre cables and in particularto a composite cable construction including optical fibre cable elements.

An objectofthe invention isto achievesuch a cable construction which is simple in structure, provides adequate protectionforthefibresand is suitable for the provision of a range of services including wide band operation.

According to the invention in its broadest aspect, there is provided a composite cable construction comprising a longitudinal former having along its length a plurality of grooves extending parallel to its longitudinal axis to receive loosely-located optical fibre cable elements, the dimensions of the grooves being such as to allow the optical fibre elements to lie as close to the neutral axis as possible.

By careful design and dimensioning of such a cable beneficial performance and costs are obtained. The cable is nottwisted noris itasymmetric in appear ance.The necessity for helical laying of the transmis sion elements is avoided by locating theglassfibre transmission elements close to the neutral axis of the cable. Hence tensile and compressive effects are minimised. Further, as the more easily extensible transmission elements are the metallic ones, then a cable which is put around a bend but is free to rotate will twist into a position such thatthe least deformable (stiffer) transmission elements will automatically be aligned along the neutral axis of curvature.

Embodiments of the invention will now be de scribed byway of example with reference to Figs. 1 to 6 of the accompanying drawings, in which Figs. 1 to 5 show cross-sections through a composite cable con struction or partthereof.

In Fig. 1 there is shown a longitudinal former 1 of plastics material having along its length a plurality of grooves 2 extending parallel to its longitudinal axis, i.e. not arranged in a helix. Along its axis may be positioned a discrete strength member 3 of steel or glass-reinforced plastics material. The grooves 2 will accept loosely-located transmission elements in the form of optical fibre elements 4 dimensioned to fit in the space defined by radius n and the angle of intersection of the lines AB/CD. All four grooves 2 may be occupied by optical fibre elements 4to form a quad.

It will be noted that the optical fibre elements 4are allowed to lie as close to the neutral axis of the cable former as possible.

As shown in Fig. 2 the grooves 2 may accommodate alternately an optical fibre element 4 and a conven tonal electrically conductive cable element 5.

As shown in Fig. 3, the former 1 and its contents may be surrounded buy a plastics sheath 6.

Furthermore, as shown in Fig. 4, the assembly may befullyfilled by injecting petroleumjelly7orsimilar material into the g rooves 2.

In construction shown in Fig. 5, the sheath informed of a laminate having an overlapping metal tape 8 underthe plastics portion 6. The central strength member 3 is of copper-clad steel. The elements 3 and 8 can serve as the inner and outer conductors respectively of a coaxial cable. In this construction it is assumed that all four grooves 2 are occupied by optical fibre elements 4 to form a quad inside the coaxial cable.

By way of theoretical explanation, reference will now be madetothediagram of Fig. 6.

The distanced is the most important in the design of this cable. This is minimised by the use of the minimum safe dimension forthe coating ofthefibre, the wall ofthe profile where it adheres to the strength member and the radius of the strength member itself.

In the fully optimised design the strength member and the profile unit are of a homogenous material such as glass reinforced plastics rod sothatthe interslot distances on the profile are at a minimum while the effective quantity of strength-giving material is at a maximum.

The cable has maximum tensile and bend limits which may be calculated as shown below. The effective maximum permissible strainforglass fibre elements is taken to be 1% for each of calculation.

Metal components are relatively unaffected by strains ofthisorder.

Permissible tensile load T T max = A x E WhereAisthe cross sectional 100 area of the cable + E Permissible bend radius R R min = 100d Sayd=2mm then maximum permissible bend radius = 200 mm It should also be noted that at the cable extremities (say overthe last 10 metres), bends of smaller radius than the design radius can be accommodated without ill effect. This is because the fibre elements are not physicallytrapped but over a long length are held in place by weight and friction. At the extremities of the cable the elements slide easily and the relatively small radius bends associated with terminating practice are easily accommodated without deleterious effects.

1. Acomposite cable construction comprising a longitudinal former having along its length a plurality of grooves extending parallel to its longitudinal axis to receive loosely-located optical fibre cable elements, the dimensions ofthe grooves being such asto allow the optical fibre cable elements to lie as close to the neutral axis as possible.

2. A composite cable construction as claimed in claim 1 in which the former contains a central reinforcing element.

3. A composite cable construction as claimed in claim 2 in which a metallic tape is wrapped around the former and in which the reinforcing element and the metallictape serve as the inner and outer conductors respectively of a coaxial cable.

4. A composite cable construction as claimed in claim 1 or 2 in which at least one of the grooves

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Optical fibre cables This invention relates to optical fibre cables and in particularto a composite cable construction including optical fibre cable elements. An objectofthe invention isto achievesuch a cable construction which is simple in structure, provides adequate protectionforthefibresand is suitable for the provision of a range of services including wide band operation. According to the invention in its broadest aspect, there is provided a composite cable construction comprising a longitudinal former having along its length a plurality of grooves extending parallel to its longitudinal axis to receive loosely-located optical fibre cable elements, the dimensions of the grooves being such as to allow the optical fibre elements to lie as close to the neutral axis as possible. By careful design and dimensioning of such a cable beneficial performance and costs are obtained. The cable is nottwisted noris itasymmetric in appear ance.The necessity for helical laying of the transmis sion elements is avoided by locating theglassfibre transmission elements close to the neutral axis of the cable. Hence tensile and compressive effects are minimised. Further, as the more easily extensible transmission elements are the metallic ones, then a cable which is put around a bend but is free to rotate will twist into a position such thatthe least deformable (stiffer) transmission elements will automatically be aligned along the neutral axis of curvature. Embodiments of the invention will now be de scribed byway of example with reference to Figs. 1 to 6 of the accompanying drawings, in which Figs. 1 to 5 show cross-sections through a composite cable con struction or partthereof. In Fig. 1 there is shown a longitudinal former 1 of plastics material having along its length a plurality of grooves 2 extending parallel to its longitudinal axis, i.e. not arranged in a helix. Along its axis may be positioned a discrete strength member 3 of steel or glass-reinforced plastics material. The grooves 2 will accept loosely-located transmission elements in the form of optical fibre elements 4 dimensioned to fit in the space defined by radius n and the angle of intersection of the lines AB/CD. All four grooves 2 may be occupied by optical fibre elements 4to form a quad. It will be noted that the optical fibre elements 4are allowed to lie as close to the neutral axis of the cable former as possible. As shown in Fig. 2 the grooves 2 may accommodate alternately an optical fibre element 4 and a conven tonal electrically conductive cable element 5. As shown in Fig. 3, the former 1 and its contents may be surrounded buy a plastics sheath 6. Furthermore, as shown in Fig. 4, the assembly may befullyfilled by injecting petroleumjelly7orsimilar material into the g rooves 2. In construction shown in Fig. 5, the sheath informed of a laminate having an overlapping metal tape 8 underthe plastics portion 6. The central strength member 3 is of copper-clad steel. The elements 3 and 8 can serve as the inner and outer conductors respectively of a coaxial cable. In this construction it is assumed that all four grooves 2 are occupied by optical fibre elements 4 to form a quad inside the coaxial cable. By way of theoretical explanation, reference will now be madetothediagram of Fig. 6. The distanced is the most important in the design of this cable. This is minimised by the use of the minimum safe dimension forthe coating ofthefibre, the wall ofthe profile where it adheres to the strength member and the radius of the strength member itself. In the fully optimised design the strength member and the profile unit are of a homogenous material such as glass reinforced plastics rod sothatthe interslot distances on the profile are at a minimum while the effective quantity of strength-giving material is at a maximum. The cable has maximum tensile and bend limits which may be calculated as shown below. The effective maximum permissible strainforglass fibre elements is taken to be 1% for each of calculation. Metal components are relatively unaffected by strains ofthisorder. Permissible tensile load T T max = A x E WhereAisthe cross sectional 100 area of the cable + E Permissible bend radius R R min = 100d Sayd=2mm then maximum permissible bend radius = 200 mm It should also be noted that at the cable extremities (say overthe last 10 metres), bends of smaller radius than the design radius can be accommodated without ill effect. This is because the fibre elements are not physicallytrapped but over a long length are held in place by weight and friction. At the extremities of the cable the elements slide easily and the relatively small radius bends associated with terminating practice are easily accommodated without deleterious effects. CLAIMS

4. A composite cable construction as claimed in claim 1 or 2 in which at least one of the grooves in the former contains an electrically-conductive cable element.

5. A composite cable construction substantially as described with reference to the accompanying drawings.