MANUFACTURE OF LIGHT TRANSMISSION GLASS

摘要

PURPOSE:To obtain a material preform for the title glass fibers having a high strength, and slight light transmission loss and strain, from a silica doped with nitrogen (or other oxide). CONSTITUTION:The inside 22 of the porous glass tube 21 comprising the atmosphere of an NH3-containing gas is heated to produce nascent nitrogen, which is reacted with the porous inner surface of the tube 21 to form glass doped with nitrogen. The content of SiOxNy(S) on the pore surfaces of the tube 21 decreases with increasing distance from the surface; the part 23 with a high S content, and the part 24 with a low S content. The porous glass tube is heated in the vacuum or atmosphere of an inert gas at a high temperature to fill the pores, forming a transparent glass tube. The resulting tube is mounted on a lathe and heated at a higher temperature while being rotated to form a rod free from the hole 22'. A self-convergent preform having a refractive index which is the highest at the center and decreases toward the outer periphery.