GB2129158A

GB2129158A - Optical fibre cable

Info

Publication number: GB2129158A
Application number: GB08328212A
Authority: GB
Inventors: Charles Robert Hand; John Carswell Smith
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1982-10-28
Filing date: 1983-10-21
Publication date: 1984-05-10
Also published as: DE3338485A1; ES275332U; ES275332Y; GB8328212D0; NO833763L

Abstract

An optical fibre cable resistant to a nuclear blast comprises a conventional optical cable (10) surrounded by a heat insulating material (e.g. fibreglass, PTFE etc.) (12) and a sacrificial, flame-retardant outer jacket (14) (e.g. polyurethane). <IMAGE>

Description

SPECIFICATION Optical fibre cable This invention relates to optical fibre cable and, more particularly, to such cable that is able to function after exposure to intense light and heat radiation such as might be experienced in a nuclear explosion.

The use of light signals and optical fibres is to a considerable extent displacing the use of electric current and standard metal conductors for the transmission of data and communication signals.

The use of optical fibres requires that they be incorporated in cables in such a way that they are protected from environmental and other usage conditions. Thus, various cable constructions have been devised that protect the fibre from normal environmental and use conditions in a generally satisfactory manner.

With the increased usage of optical fibre cable by the military, a requirement has been specified that the cable must be able to survive and operate after a nuclear event, for example, a nuclear bomb explosion. Thus, the cable must be sufficiently rugged ta withstand normal environmental and use conditions and must additionally be constructed to withstand the intense light, high winds and high temperature developed during and after a nuclear blast. That is, after the blast, the optical fibre must be capable of transmitting light and the cable must be sufficiently intact to withstand the forces imposed by debris scattered about by an explosion as well as the other normal environmental and use conditions.

Accordingly, it is an object of this invention to provide an optical fibre cable particularly suited to survive a nuclear event and to protect the optical fibre in such a way that it is not broken or melted during the event.

According to one aspect of the invention there is provided an optical fibre cable comprising a sheathing, optical fibres contained within the sheathing and a heat-insulating material surrounding the sheathing.

According to another aspect of the invention there is provided an optical fibre cable comprising a sheathing, optical fibres contained within the sheathing panda heat-insulating material surrounding the sheathing and a heat-insulating material is in turn surrounded by a sacrificial jacket which is flame-retardent. In this way the initial light pulse generated during the explosion will char or vapourise the sacrifical jacket without unduly damaging the heat-insulating material or the cable surrounded by it.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawing in the form of a crosssection through a cable constructed in accordance with the invention.

The drawing illustrates a generally conventional cable 10 surrounded by a heat insulating material 12 and a sacrificial, fiame retardent jacket 14. The generally conventional cable may be of any suitable type and in the embodiment disclosed here includes a pair of longitudinal strength members 16, 1 6 located on diametrically opposite sides of the cable axis. These strength members 16, 16 can be any of a variety of materials to provide tensile strength to the cable and in this embodiment are cords of aramid fibre of 7100 Denier (a measure of weight per unit length, typically given in grams per 9,000 meters). An example of a suitable aramid fibre usable with this invention is that sold by E. I. Dupont Company under the trademark KEVLAR.

Adjacent the strength members 16, 1 6 are a pair of optical fibres 18, 1 8 also located on diametrically opposite sides of the cable axis. Any suitable optical fibre composition can be used, but a typical fibre includes a core 1 spa and an outer cladding 1 sub. The fibre is preferably formed so as to exhibit resistance to gamma radiation to minimise radiation-induced optical absorption.

One type of fibre found usable for this purpose includes a core 1 8a doped with germanium and a cladding 1 8b doped with fluorine. The strength members 16, 1 6 and fibres 18, 18 are located in abutting relationship and are helically twisted about the cable axis.

The bundle formed by the strength members 16, 16 and fibres 18, 18 is wrapped with fibre cord strength members 20 to protect the optical fibres. The fibre cords 20 can also be aramid fibres sold under the trademark KEVLAR, but in that case are smaller cords of about 1420 Denier.

Preferably, the strength members 20 are helically wrapped around the bundle of strength members 1 6 and fibres 1 8. Around the strength members 20 is formed a conventional sheathing 22 that holds the strength members 20 in place and provides additional protection for the fibres. The sheathing 22 can be a composite of paper or polyester wrapped around the strength members 20, and an extruded jacket. This specific structure is not illustrated as it is generally conventional. It should be specifically understood that other sheathings can be used.

In accordance with this invention, the sheathing 22 is wrapped with heat insulating material 12 of sufficient thickness to withstand anticipated heat levels in a thermal explosion. The heat insulating material 1 2 is a glass fibre material commonly referred to as fibreglass. The fibreglass is preferably coated with a fluorocarbon, frictionreducing material such as TEFLON (R.T.M.). In this way, friction resistance is reduced during the fabrication of the cable. This fibreglass can be obtained in the form of a yarn or a tape and is usable in either form. If desired, the fibreglass yarn can be braided into a woven material and can be used in this form. The fibreglass is preferably also helically wrapped around the sheathing 22. Other material suitable for use as the heat insulating material 12 is an organic tape such as aramid or polytetrafluoroethylene.

The sacrificial, flame retardant jacket 14 is extruded over the fibreglass 1 2 and can be a flame-retardant polyurethane material such as that sold under the trademark ESTANE sold by B.

F. Goodrich or HALAR sold by Allied Chemical.

HALAR is a fluoro polymer resin comprising a oneto-one alternating copolymer of ethylene and chorotrifluoroethylene. This material is ablative in that it vaporises at high heat, but other types of flame-retardant materials can be used. For example, materials that char rather than vaporise could also be used. In some instances, the use of the sacrificial jacket may not be necessary. In those instances, the heat insulating material should be made thicker to help absorb the initial heat generated during the blast.

During a nuclear explosion, there is first developed a thermal flash in the form of intense light of about 12 to 20 second duration. This light will ignite the exposed surface of the sacrificial jacket 14 causing it to vaporise or char. After the flash, there is a high wind that will extinguish the combustion of the jacket. Thereafter, the intense heat following the blast is resisted by the insulating material 12 which is left substantially intact as is the cable 10. Because the cable 10 is intact, it can operate as it was designed to withstand normal environmental and use conditions.

Claims

1. An optical fibre cable comprising a sheathing, optical fibres contained within the sheathing and a heat-insulating material surrounding the sheathing.

2. An optical fibre cable comprising a sheathing, optical fibres contained within the sheathing and a heat-insulating material surrounding the sheathing, wherein the heatinsulating material is in turn surrounded by a sacrificial jacket which is flame-retardant.

3. An optical fibre cable in accordance with claim 1 or 2 wherein the heat-insulating material is fibreglass.

4. An optical fibre cable in accordance with claim 1 or 2 wherein the heat-insulating material is an organic tape selected from the group consisting of aramid and polytetrafluoroethylene.

5. An optical fibre cable in accordance with claim 3 wherein the fibreglass is coated with a friction-reducing material.

6. An optical fibre cable in accordance with claim 3 wherein the fibreglass is helically wrapped around the sheathing.

7. An optical fibre cable in accordance with claim 3 wherein the fibreglass is braided around the sheathing.

8. An optical fibre cable in accordance with claim 3 wherein the fibreglass is in the form of tape wrapped around the sheathing.

9. An optical fibre cable in accordance with claim 2 wherein the flame-retardant jacket is polyurethane.

10. An optical fibre cable in accordance with claim 2 wherein the flame-retardant jacket is ablative.

11. An optical fibre cable in accordance with claim 2 wherein the flame-retardant jacket chars when exposed to extreme heat.

1 2. An optical fibre cable substantially as described with reference to the accompanying drawings.