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 μm (Silica A). 2) The bubble could be removed by using the decanted Silica A only or by purifying at 1000°C. 3). The Cr-inclusions could be removed by purifying at 1000°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