Methods of coating lightguide fiber and product produced thereby

Abstract

A coating material is applied to drawn lightguide fiber in a manner which substantially prevents the inclusion of bubbles and which causes the fiber to be disposed substantially concentrically within the coating layer. The lightguide fiber is advanced through a continuum of coating material, which extends from a free surface of a reservoir and through two dies that are arranged in tandem, at a velocity which causes air to be entrained in the coating material. A pressure gradient is established between portions of the first die adjacent to its exit orifice. A first one of the dies communicates with the reservoir and the second die and further communicates at the interface of the dies with a pressurized supply of the coating material. The pressurized flow sufficiently enhances the pressure gradient in the first die and establishes sufficient volumetric flow of coating material upwardly through the first die to cause any bubbles in the coating material on the advancing fiber to be removed by recirculating streamlines and to be moved upwardly into the reservoir. The bubbles are substantially immediately removed from the reservoir by providing fluid exit channels through which bubble entrained coating material exits the reservoir in the vicinity adjacent the first die. Not only is the coating in the fiber substantially free of entrained air as it leaves the second die, but coalescing bubbles do not misalign the fiber and the fiber is disposed concentrically within the coating because of a precentering effect of the first die and enhanced self-centering caused by pressure in the chamber.