PRODUCTION OF RARE EARTH ELEMENT ADDED OPTICAL FIBER

摘要

PURPOSE:To decrease structure unmatching losses and to reduce the cost of production by heating a soot preform consisting of a soot compsn. having a lower viscosity in the soot layer on the outer side than in the soot layer on the inner side at the time of a high temp. CONSTITUTION:The soot preform 1 of the soot compsn. having the lower viscosity in the soot layer 3 on the outer side than in the soot layer 2 on the inner side at the time of the high temp. is heated to increase the bulk density of the outer soot layer 3 and thereafter a rare earth element soln. is penetrated into the inner soot layer 2. The outer soot layer 3 is constituted of silica glass doped with germanium and/or phosphorus and the inner soot layer 2 is constituted of pure silica glass in such a case. The outermost layer consisting of pure silica glass is preferably provided on the further outer side of the outer soot layer 3 of the soot preform 1. The intrusion of impurities into the core where light power concentrates is obviated in this way and the structure unmatching losses are decreased. The high-quality rare earth added optical fiber is thus obtd. at a low cost.