PURPOSE: To produce the quartz optical fiber having a three-layered structure consisting of core-clad-outer layer, having the compressive strain remaining in the outer layer and having excellent flaw resistance and fatigue characteristic by the simple process.
CONSTITUTION: An intermediate base material for the optical fiber consisting of the fine particles of glass having the three-layered structure consisting of the core-clad-outer layers is formed by a VAD method. A transparent glass rod consisting of a part of the core and the clad is otherwise performed, and the remaining clad and the outer layer are made in the form of the fine particles of glass around this rod to form the intermediate base material for the optical fiber. The intermediate base material is so formed that the bulk density of the fine particles of glass of the clad is larger than a prescribed value and the bulk density of the fine particles of glass of the outer layer is smaller than the prescribed value at this time. The base material doped with fluorine only into the outer layer of the small bulk density is obtd. when this intermediate base material for the optical fiber is made into transparent glass in a fluorine-contg. gaseous atmosphere. The tension at the time of drawing is born by the clad when this base material is made into a fiber by melting and drawing. The compressive stress eventually remains in the outer layer after the release thereof. The tensile stress is, therefore, relieved by this residual stress even if the tensile stress acts on the fiber after the production.
YAMADA SHIGETOSHI
KOIDE TOSHIO
TAKAHASHI KOICHI
