Metallic-Glass Coated Optical Fibres

This invention relates to optical fibres and, in particular, to methods of providing them with coatings.

According to the present invention there is provided a method of providing an optical fibre with a coating including the step of employing a laser beam to cause local heating of the coating material on an optical fibre whereby to induce a physical or chemical change therein.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

FIG. 1 shows the layout of an on-line coating system for the performance of a coating method according to the present invention, and

FIG. 2 illustrates in more detail and on a larger scale the laser function region of FIG. 1.

It has previously been proposed to improve the fatigue performance of optical fibres by use of coatings which inhibit flaw growth by providing resistance to attack by moisture. Metallic glass coatings have been suggested for this hermeticity purpose. Optical fibres with metallic glass coatings are also useful for sensor applications. For that purpose short fibre lengths have been coated with metallic glass by sputtering. Fibre optic sensors are also known which are produced by glueing fibre to metallic glass strips.

The methods proposed by the present invention may be carried out on-line with the fibre drawing process and thus permit on-line coating of multi-kilometer lengths to be achieved.

Referring firstly to FIG. 1, a newly drawn fibre 1, which may be drawn from a conventional preform or crucible indicated generally at 2, is passed through a crucible 3 containing a suitable molten metallic-glass forming alloy 4, for example Fe-Ni-B or Ni-Zr, and exits through an orifice at the bottom of the crucible 3 as an alloy coated fibre 5. The coated fibre 5 is passed through the focus 6.sup.1 of a laser beam output from a laser 6 which serves to melt the metal layer locally. The molten alloy cools rapidly and therefore produces a metallic-glass coated fibre at 7, the coating being fused to the fibre. A polymer coating may be applied in a conventional manner at 8 if desired. The coated fibre is taken up on a spool 9.

The laser fusion region is indicated more clearly in FIG. 2. The fibre 1 coated with alloy 4, which is expected to be crystalline, is passed in the direction of the arrows through the laser focus 6.sup.1 resulting in a molten zone 10 which subsequently cools to produce the metallic glass coated fibre 7.

Whereas the invention has so far been described with reference to metallic glass coatings on optical fibres, the laser fusion coating process is applicable to the provision of other coatings applied at speed to optical fibres for example, ceramics or polymers, in which the fibre is coated by passing it through a bath of a coating material and the coating material is fused to the glass of the fibre as a result of rapid passage through the focus of the laser beam. As an alternative to providing the metal or other coating to the fibre by dip coating, that is where the fibre is passed through a crucible of the molten metal or liquid coating material, the coating may be applied to the fibre by other means, for example a vapour phase technique may be employed.

Whereas in the above described example the laser serves to fuse the coating to the fibre, the effect of the laser is basically to cause local heating which induces a physical or chemical change in the coating, such as glassifying a metal coating or inducing a phase transformation in the coating material, for example curing a polymer.