Abstract: A method and apparatus for high velocity dual coating optical fibers includes passing the fiber to be coated through an entrance die into a coating reservoir, to which liquid coating material is supplied under pressure. The diameter of the die passage and the pressure of the fluid is sufficient to prevent air from entering the reservoir. The coated fiber is passed through a centering and sizing die wherein the recirculation of excess coating material is controlled to produce centering forces on the fiber at the high fiber velocity, and wherein the initial coating is sized. The fiber is then passed through a second coating reservoir into an exit die which sizes the second coating. Upon leaving the exit die, the coatings are cured.

Abstract: Fiber bow makes mass fusion splicing of optical fiber difficult and this is undesirable. We have found that fiber bow can be significantly reduced if the fiber that is being drawn from a heated optical fiber preform is caused to run through a tubular cooling chamber that extends from the draw furnace, the cooling chamber comprising a tube of inner diameter d.sub.1 <35 mm, preferably <20 mm. In a preferred embodiment the cooling chamber includes an upper cooling chamber of inner diameter d.sub.2 >d.sub.1, with a transition element providing a smooth transition between the two chambers. The cooling chamber desirably is free of turbulence-causing air leaks and/or geometrical features.

Abstract: A fiber drawing apparatus is provided with an improved fiber draw furnace wherein an inner zirconia tube is surrounded by a radially-spaced annular insulating region of magnesia within a silica beaker. While the magnesia has a melting point approximately the same as zirconia, the electrical conductivity of magnesia is substantially lower, enabling it to withstand higher RF power. Moreover magnesia is more soluble than zirconia in silica, reducing the likelihood of particulate contamination of the fiber.