Method for manufacturing a preform for drawing optical fibres

Abstract From the Canadian patent

A process is disclosed for producing an optical fiber comprising forming a tubular glass body having at least one doped layer, at least one concentric layer each layer, having a different index of refraction and a hollow center. The glass body is heated until the softening point is reached, and is then drawn into a glass fiber. During drawing, a partial vacuum is maintained in the hollow center of the tubular glass body, the partial vacuum being of sufficient magnitude to reduce the evaporation of doping material from the interior of the tubular glass body and thereby effectively prevent a reduction in the index of refraction in the center of the optical fiber.