Fracture origins of optical fibers fabricated by hybridized process

Fracture origins of single-mode optical fibers that were produced by the CIP hybridized process consisting of overcladding a VAD-derived core rod with silica glass made from commercial silica powder were studied. It was found that there were many inclusions that caused failure of the fiber at the screening test. To identify the inclusions, the EPMA technique was successfully used and new internal defects such as a Cr, a Cr-Fe, and a Zr inclusions were found. By investigating the manufacturing process precisely, stainless steel particles and Cr₂ O₃ particles in the silica powder were found to become origins of the fractures. Further, the removal of Cr₂O₃ particles by the reaction with chlorine gas at high temperature was studied, and its dependence on the reaction temperature and on the chlorine content was clarified. It was also suggested that the initial particle size of a Cr₂O₃ particle was an important factor for its elimination. The results obtained by this study should be used to remove both the Cr and the Cr-Fe inclusions