| 摘要 |
PURPOSE:To stably produce the titled preform for optical fiber having a high numerical aperture by forming a layer of quartz glass added with fluorine on the outer periphery of a pure quartz glass layer which is provided on the outer periphery of a rod to form the outermost periphery of a core rod. CONSTITUTION:A starting rod consists of quartz glass contg. GeO2 necessary to control the specific refractive index difference from pure quartz glass to >=1.5%, and is used as the core rod 1. A thin pure quartz glass layer having a thickness 1/60-1/125 times the outer diameter of the starting rod is provided on the outer periphery of the starting rod. The layer of quartz glass added with fluorine is further furnished on the outer periphery. The clad pipe 2 is formed with quartz glass whose refractive index difference is controlled to <=-0.3% by the addition of fluorine. Since the fluorine-added layer is provided on the outer periphery of the core rod 1, the vitrification temp. of quartz glass is decreased, the deformation of the core glass is controlled to the minimum in spite of direct vitrification for many hours, the thickness of the coated pure quartz glass layer can be sufficiently kept even in the succeeding high-temp. process such as drawing, and the degree of freedom in the processing can be expanded. |
