Studies on the strength of optical fiber fabricated by a hybridized process

Strength of single-mode optical fibers that were produced by a hybridized process consisting of overcladding a VAD-derived core rod with silica glass made from commercial silica powder was studied. There were such defects as a Zr-containing inclusion (Zr-inclusion), a bubble and two kinds of Cr-containing inclusions (Cr-inclusions) found in the fiber. These defects caused failure of the fiber at a proof test. In order to make a strong fiber, removal of the defects were studied and the following results were obtained as follows. 1) The Zr-inclusion could be removed by decanting an aqueous suspension of silica powder having an average diameter of 10 /spl mu/m (Silica A). 2) The bubble could be removed by using the decanted Silica A only or by purifying at 1000/spl deg/C. 3). The Cr-inclusions could be removed by purifying at 1000/spl deg/C in helium gas containing more than 30 vol.% chlorine. The strongest fiber fabricated had a break probability as low as 0.01/km in a proof test of 0.7% elongation for 1 s.