Modal Structure of an MCVD Optical Waveguide Fiber

Multimode lightguides, produced by the Modified Chemical Vapor Deposition (MCVD) process, are expected to be of continuing importance to the Bell System. Such lightguides with bandwidths exceeding 1 GHz-km have been produced in the manufacturing plant. The unique MCVD process produces the index gradient in the core by depositing many layers of material with different compositions, leading to a ripple effect in the profile. Other imperfections in the MCVD process include certain mechanical limitations, difficulties at the core-cladding interface, and the altering of the core center index (burn-off) during the collapse of the preform. These imperfections in the MCVD process lead to a unique modal structure in the fiber, which * Bell Laboratories, Princeton, N.J.