GB2127170A

GB2127170A - Fibre optic cables

Info

Publication number: GB2127170A
Application number: GB08226314A
Authority: GB
Inventors: Lyndon Reginald Spicer
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1982-09-15
Filing date: 1982-09-15
Publication date: 1984-04-04
Also published as: DE3332731A1

Abstract

A joint between two optical fibres (5) is made by means of a connector (1) formed of a memory metal. The fibres are inserted into a bore (6) from opposite ends thereof whilst the connector is at a first temperature at which the bore (6) is of a larger diameter than the fibres. The connector is then caused or allowed to achieve an optical fibre working range temperature, at which the bore assures a memorised diameter smaller than the fibre diameter, thus clamping the fibres therein. Preferably the memory metal is an non-reversible one and the first temperature is lower than the working temperature range, for ease of connection in the field. Bore 6 may be drilled with a laser and silvered. Cables with two optical fibres may be joined (Figure 2, not shown). <IMAGE>

Description

SPECIFICATION Fibre optic cables This invention relates to fibre optic cables and in particular to the jointing of optical fibres.

Various techniques have been developed for jointing optical fibres. There are techniques in which two fibre ends are held in alignment by a jointing ferrule.

Other techniques include fusion splicing the fibre ends.

The present invention relates to the use of memory metal to form a ferrule for jointing. A connector for optical fibres is described in the magazine CME July 1981 on page 6. In this connector a beryllium copper tube contains three strips of Nitinol, a nickel-titanium alloy with a mechanical memory, defining an axial cavity for the fibres. The Nitinol strips are annealed in a flat shape and bent at room temperature for insertion into the tube. If the connector is heated the strips tend to flatten, thus distorting the tube and opening up the axial cavity. The fibre ends can then be inserted into opposite ends of the cavity and, upon cooling of the connector, become clamped therein as a result of the Nitinol strips returning to the bent configuration.

According to the present invention there is provided a connector, for connecting together the ends of two optical fibres, comprising a solid body of a memory metal having a circular bore therethrough which is of a diameter larger than the fibres to be connected at a first temperature outside the working temperature range of the fibres and which assumes a diameter smaller than the fibres within the working temperature range of the fibres, whereby the fibres an be inserted into alignment in the bore when the body is at the first temperature and will be held clamped in the bore within the working temperature range of the fibres.

According to a further aspect of the present invention there is provided a method of jointing two optical fibres including the steps of inserting the end of each fibre into a cylindrical bore of a connector from opposite ends thereof whilst the connector is at a first temperature, the connector being comprised of a memory metal whereby the bore has a diameter larger than the fibres to be connected at the first temperature and a diameter smaller than the fibres within the working temperature range of the fibres, and allowing or causing the connector temperature to rise to a value in the working temperature range, whereby the fibres become clamped within the connector.

According to a further aspect of the present invention there is provided a method of manufactur ing a connector, for connecting together the ends of two optical fibres, including the steps of drilling a circular bore through a body of a memory metal and annealing the drilled body, whereby the circular bore has a diameter larger than the fibres to be connected at a first temperature outside the temperature range of the fibres and has a diameter smaller than the fibres within the working temperature range of the fibres.

Preferably the memory metal is of the nonreversible type so that once the fibres have been inserted and a working temperature reached, the bore size will not become larger than the fibres even if the first temperature is again reached. Thus the metal undergoes a permanent atomic bonding change which cannot be reversed, at least not at the first temperature.

Preferably the first temperature is below the working temperture range so that the connector can be kept cold in a freezer or a flask of dry ice until required for connecting fibres together.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which Figure 1 shows a longitudinal section through a connector according to an embodiment of the invention and two optical fibres to be connected thereby, and Figure 2 shows schematically two connectors of Figure 1 used in connecting together the optical fibre cables each including two fibres.

The connector 1 shown in Figure 1 comprises a substantially cylindrical body of a memory metal, preferably a non-reversible memory metal. The connector has a bore therethrough comprising portions 2 and 3 of a diameter and a shape to facilitate insertion of plastically-clad optical fibres 4, whose cladding has been removed from a portion of the fibre ends to expose the optical fibres 5 proper.

Portion 6 of the bore is of a circular cross-section and a diameter comparable with the optical fibres 5, typically 50+2 microns or greater, and is peferably drilled with a laser beam so that the size and internal finish can be strictly controlled. The exact diameter of the bore 6 when drilled, for example at room temperature, will be dependent on the composition and properties of the memory metal, employed, the subsequent annealing process employed to memorise a smaller bore diameter, and the temperatures at which the connector is stored and employed.

For ease of use in the field, in particular, when restoring severed optical fibre communications links it is preferred to store the connectors in a very cold environment, such as a flask of dry ice, at a temperature at which the bore 6 is of a larger diameter than the fibres, and to rely on the temperature of the surroundings (i.e. the working temperature range of the fibres) for warming up the connector, in order to clamp the fibres therein, thereby causing the bore 6 to revert to a memorised diameter smaller than fibre diameter. In order that subsequent drops in temperature of the connector do not cause the fibres to become loose, the memory metal is preferably non-reversible. When the connector is warmed up the centre bore portion 6 will collapse uniformly to hold the fibres securely.

Ideally, the ends of optical fibres 5 should be polished flat in a plane normal to their length such that they may abut in the bore 6. It is desirable in optical joints that the fibres should lie exactly in line with one another or there is attentuation due to light being lost. By virtue of the close tolerances achievable with a laser drilled bore and the subsequent crushing down of the memory metal connector onto the fibres the attentuation problem is minimised with the memory metal connectors of the present invention.

In order to minimise light attentuation when the fibre ends are not normal to their length, or when they do not quite abut within the bore 6, the latter may be provided with a mirror finish. This may be achieved by coating the inside of the bore with mercury, such as by mixing mercury and nitric acid, pouring the mixture through the bore and subsequently washing the bore out with water. The mirror finish ensures that any light escaping from one fibre can be reflected back into the other fibre.

An optical fibre communications cable may basically comprise a central strength member 7 of, for example Kevlar, two optical fibre elements 8 and a cable jacket 9 (Figure 2). In order to joint two such cables the optical fibres thereof may be connected by memory metal connectors 10, as described above with reference to Figure 1. In order to perform the jointing quickly in the field, intead of connecting the respective strength members 7, the strength member can be effectively reinstated over the joints by means of a two piece (split longitudinally) sleeve arrangement 11, clamped onto the respective cable jackets 9 by means not shown, which serves also to protect the connectors 10. The space around the fibre joints may be filled with a resin.

Claims

1. A connector, for connecting together the ends of two optical fibres, comprising a solid body of a memory metal having a circular bore therethrough which is of a diameter larger than the fibres to be connected at a first temperature outside the working temperature range of the fibres and which assumes a diameter smaller than the fibres within the working temperature range of the fibres, whereby the fibres can be inserted into alignment in the bore when the body is at the first temperature and will be held clamped in the bore within the working temperature range of the fibres.

2. A connector as claimed in claim 1, wherein the memory metal is of the non-reversible type.

3. A connector as claimed in claim 1 or 2, wherein the first temperature is below the working temperature range.

4. A connector as claimed in any one of the preceding claims, wherein the bore is provided with a mirror finish.

5. A connector as claimed in any one of the preceding claims, wherein the bore is drilled by a laser.

6. A method of jointing two optical fibres includ ing the steps of inserting the end of each fibre into a cylindrical bore of a connector from opposite ends thereof whilst the connector is at a first temperature, the connector being comprised of a memory metal whereby the bore has a diameter larger than the fibres to be connected at the first temperature and a diameter smaller than the fibres within the workig temperature range of the fibres, and allowing or causing the connectortemperture to rise to a value in the working temperature range, whereby the fibres become clamped within the connector.

7. A method as claimed in claim 6, wherein the memory metal is of the non-reversible type.

8. A method as claimed in claim 6 or 7, wherein the first temperature is below the working temperature range.

9. A method of manufacturing a connector, for connecting together the ends of two optical fibres, including the steps of drilling a circular bore through a body of a memory metal and annealing the drilled body, whereby the circular bore has a diameter larger than the fibres to be connected at a first temperatue outside the temperature range of the fibres and has a diameter smaller than the fibres within the working temperature range of the fibres.

10. A method as claimed in claim 9, wherein the memory metal is of the non-reversible type and wherein the first temperature is below the working temperature range.

11. A method as claimed in claim 9 or 10 including the step of providing the bore with a mirror finish.

12. A connector for connecting together the ends of two optical fibres substantially as herein described with reference to and as illustrated in Figure 1 of the accompanying drawings.

13. A method of jointing two optical fibres using a connector as claimed in any one of claims 1 to 5 or 12.

14. A method of manufacturing a connector as claimed in claim 9 and substantially as herein described with reference to Figure 1 oftheaccom- panying drawings.

15. A joint between two cables incorporating optical fibres, wherein the fibres of the two cables are connected by connectors as claimed in any one of claims 1 to 5 or 12.

16. Ajoint between two cables incorporating optical fibres substantially as herein described with reference to Figure 2 of the accompanying drawings.