Compagnie Generale D'electricite

Robert Pascal

Christian Le Sergent

Michel Liegois

The blank is made from a tube of silica with a layer of other glass coated on its inner surface. The said other glass is doped with P.sub.2 O.sub.5 for example to increase its refractive index. The blank is then reduced in diameter from a tube to a rod by heating a region of the tube while it rotates in a glassmaker's lathe. The heated region is moved back and forth along the length of the tube until it is finally reduced to a rod. One effect of the moving heated zone is to evaporate some of the doping material, and the vapour tends to move along the tube ahead of the heated zone until it is eventually shifted out of the ends of the tube. To minimize this loss the back and the forth movement of the heated zone includes a sudden step forward at the end of each pass before returning in the opposite direction. This has the effect of jumping the heated zone ahead of the escaping doping material which is then pushed back along the bore of the tube for the next pass, with the jump-ahead-and-reverse operation being repeated at each reversing point of the back and forth heated pass to conserve as much of the doping material as possible inside the tube and finally within the resulting glass fibre blank.

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Montlhery, France

Robert Pascal