In a chemical vapor deposition (CVD) process for manufacturing a fiber optic preform, a glass rod is inserted into the preform during the deposition of the core layer. This yields a fiber having a longitudinal eccentric index inhomogeneity which is close to the axis of the fiber....http://www.google.com/patents/US3980459?utm_source=gb-gplus-sharePatent US3980459 - Method for manufacturing optical fibers having eccentric longitudinal index inhomogeneity
