On the origin of excess loss in highly GeO/sub 2/-doped single-mode MCVD fibers

Index profile grading and elimination of the central dip have yielded the lowest loss ever reported for modified chemical vapor deposition-made highly GeO/sub 2/-doped single-mode fibers (1.33 dB/km at 1550 nm for /spl Delta/=2.9%). Investigation of the angular distribution of scattering has shown that much of the optical loss in such fibers is due to anomalous scattering. This scattering arises in the region of the central dip in the refractive index profile and at the core-cladding interface.