NZ204427A

NZ204427A - Preform cable core:optical fibres in grooves

Info

Publication number: NZ204427A
Application number: NZ204427A
Authority: NZ
Inventors: R D Edwards; D D Jones
Original assignee: Int Standard Electric Corp
Priority date: 1982-06-11
Filing date: 1983-05-31
Publication date: 1986-08-08
Also published as: AU559047B2; AU1542383A; GB2123164A; GB2123164B

Description

2044 me con Priority Date(s): . f.'.. T.'?. f/.'j Complete Specification Filed: •Class: Publication Date: ...k'. ?. M .... P.O. Journal, No: .... /$ NEW ZEALAND THE PATENTS ACT, 1953 COMPLETE SPECIFICATION "OPTICAL FIBRE CABLES" WE, INTERNATIONAL STANDARD ELECTRIC CORPORATION, a Corporation of the State of Delaware, United States of America, of 320 Park Avenue, New York 22, New York, United States of America, hereby declare the invention, for which we pray that a, patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement This invention relates to optical fibre cables and in particular to a composite cable construction including optical fibre cable elements - An object of the invention is to achieve such a cable construction which is simple in structure, provides adequate protection for the fibres and 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 composite cable construction comprising a longitudinal former having along its length a plurality of deep radial grooves each of which has an optical fibre element loosely located at the bottom thereof, and a central core section, wherein the depth of said grooves is such that the distance between the axis of a so located said optical fibre element and the neutral axis of said former is short relative to the distance between the neutral axis and the said formers periphery such that each optical fibre element lays proximate the neutral axis.

By careful design and dimensioning of such a cable beneficial performance and costs are obtained. The cable is not twisted nor is it asymmetric in appearance. The necessity for helical laying of the transmission elements is avoided by locating the glass fibre transmission elements close to the neutral axis of the cable. Hence tensile and compressive effects are minimnised. 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 that the least deformable (stiffer) transmission elements will automatically be aligned along the 204427 neutral axis of curvature.

Embodiments of the invention will now be described by way of example with reference to Pigs. 1 to 6 of the accompanying drawings, in which Pigs. 1 to 5 show cross-sections through a composite cable construction or part thereof.

In Pig. 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 r and the angle of intersection of the lines AB/CD. All four grooves 2 may be occupied by optical fibre elements 4 to form a quad. It will be noted that the optical fibre elements 4 are allowed to lie as close to the neutral axis of the cable former as possible.

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

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

Furthermore, as shown in Pig. 4, the assembly may be fully filled by injecting petroleum jelly 7 or similar j N.Z. PATENT - ———■— 2 2 JAN 1986 204427 material into the grooves 2.

In the construction shown in Fig. 5, the sheath is formed of a laminate having an overlapping metal tape 8 under the 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 made to the diagram of Fig. 6.

The distance d is the most important in the design of this cable. This is minimised by the use of the minimum safe dimension for the coating of the fibre, the wall of the 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 so that the 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 strain for glass fibre elements is taken to be 1% for each of (Calculation. Metal components are relatively unaffected 204427 by strains of this order.

Permissible tensile load T T max = A x E 100 Where A is the cross sectional area of the cable + E; and E is the modulus of -elasticity.

Permissible bend radius R R min = 100 d Say d = 2 mm then minimum permissible bend radius = 200 mm * It should also be noted that at the cable extremities (say over the 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 physically trapped 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 pracvtice are easily accommodated without deleterious effects. ^v2 2 JAN 1936 RSCStVHD I g-T "UJ. . .'ML I ' ■

Claims

204427 What we claim is:

1. A composite cable construction comprising a longitudinal former having along its length a plurality of deep radial grooves each of which has an optical fibre element loosely located at the bottom thereof, and a central core section, wherein the depth of said grooves Is such that the distance between the axis of a so located said optical fibre element and the neutral axis of said former is short relative to the distance between the neutral axis and the said formers periphery such that each optical fibre element lays proximate the neutral axis.

2. A composite cable construction as claimed in claim 1 in which the central core section comprises 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 metallic tape 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 in the former contains an electically-conductive cable element. j N.Z. PATENT OFFICE 204427

5. A composite cable construction substantially as described with reference to the accompanying drawings. INTERNATIONAL STANDARD ELELCTRIC CORPORATION P.M. Conrick Authorized Agent P5/1/1466