Abstract: Glass optical fiber having a primary coating constructed from two layers (having a total thickness 50-70 .mu.m), in which the first layer on the fiber consists of UV cured acrylate resin having a modulus of elasticity at 25.degree. C. less than or equal to 5 N/mm.sup.2. The second layer is also a UV cured acrylate resin, but has a modulus of elasticity at 25.degree. C. of from 25 to 1500 N/mm.sup.2. The ratio of the thickness of the first layer to the thickness of the second layer is between 0.5 and 2.

Abstract: Optical fibres are drawn from a solid preform which consists substantially of SiO.sub.2 and doped SiO.sub.2. After leaving the heating zone, the fiber is guided through a space having a laminar gas flow to restrict the temperature drop across the fiber so that no extra stresses are incorporated in the fiber upon cooling. A device for performing this method comprises a quartz pipe through which the fiber is guided and in which a laminar gas flow is maintained.

Abstract: An improved sealing of the inlet channel of a drawing furnace for optical fibres can be achieved by using one or more silicon rubber discs having an aperture whose diameter is smaller than that of the preform.Burning of the silicon rubber discs can be checked by a choice of the material for the discs having a refractive index smaller than that of the preform so that thermal radiation is not irradiated in the disc via the preform.The silicon rubber discs are further protected by a metal screening between the discs and the interior of the drawing furnace.