Thomson-csf

Arnaud De Panafieu

Christiane Baylac

Marc Turpin

Michel Favre

Michel Faure

Michel Villard

Yves Nemaud

A process for the manufacture of a glass blank in the form of a rod from which the optical fibre is drawn, said blank being produced starting from a molten bath of glass. A first stage of the process comprises melting a mixture of starting materials having a higher impurity content (&lt;10.sup.-4) in the form of so-called transition metals then the final blank (&lt;10.sup.-7). A second stage consists in inducing separation into two solid phases (a hard phase rich in silica and a soft phase poor in silica) by drawing the blank from the bath of molten glass and by subsequently subjecting it to a thermal annealing treatment. This is followed by deep etching and by peripheral etching to eliminate the soft phase and its impurities to different extents as a function of depth, which creates a radial refractive index gradient and an optical cladding.

Process for the production of graded index optical fibres

A process yielding a glass blank in the form of a rod intended for drawing an optical fiber of the kind of self-focussing fiber i.e. having a radial refractive index gradient, having features (substantially transparency or transmission efficiency) lower than those of the fibers intended for long distance communication but sufficient for middle distance transmission, and which exhibits a lower cost than known processes. In a first stage a phase separation yields a 'hard' phase (rich in silicon) and a 'soft' phase (poor in silicon and rich in impurities) due to the drawing of a rod from a bath of molten glass through a cooling system having a strong temperature gradient and creating a radial refractive index gradient. In a second stage the soft phase is leached, eliminating the impurities contained in the soft phase but keeping safe the radial gradient. In a third stage a consolidation treatment is a pure annealing treatment rendering the hard phase more homogeneous.

Process for the manufacture of optical fibers with a radial refractive

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Arnaud De Panafieu