PURPOSE: To provide the functional preformed material of rare earth element-doped silica glass fiber useful for optical fiber amplifiers, etc.
CONSTITUTION: (A) A feedstock gas for glass formation, (B) a dopant feedstock gas for raising refractive index and (C) a second dopant feedstock gas for activating amplification characteristics are subjected to flame hydrolysis to produce fine silica glass particles, which are accumulated into a porous glass preformed material. This preformed material is immersed in a solution of a rare earth element-contg. compound and then thoroughly dried; and the resultant preformed material is immersed in a solvent soluble for the said rear earth element-contg. compound to bring the concentration distribution of the said compound in the porous glass preformed material to such a state as to be higher in the central part than in the peripheral part, and then dried again. The resultant preformed material is then sintered at elevated temperatures and transparently vitrified to produce a rare earth element-doped silica glass rod for use as core. Subsequently, the outer periphery of the glass rod is fed with a glass- forming feedstock gas for cladding to produce a porous preform, which is then sintered and transparently vitrified. Thus, the final preformed material is obtained.
SAITO FUMIO
SHIMADA TADAKATSU
