Interplay of design parameters and fabrication conditions on the performance of monomode fibers made by MCVD

An apparently undocumented loss mechanism in monomode fibers with germanium doped cores is demonstrated. This loss increases as the fiber drawing temperature and/or the germanium concentration increases. By consideration of this mechanism in the fiber design and fabrication, losses lower than previously reported have been achieved both in fiber with low germanium concentration (0.38 dB/km at 1.3 μm) and in higher doped, dispersion shifted fiber (0.37 dB/km at 1.55μm). The constraints on fiber design as a consequence of this loss mechanism are discussed.