In order to achieve the desired optical properties in optical fibers, extensive research and development efforts have been continuously dedicated to provide accurate and reproducible fabrication processes. Fabrication process for optical fibers can be divided in large by two separate processes:
(1) Preform fabrication and postprocessing
(2) Fiber drawing
“Preform” is the terminology conventionally used among optical fiber manufacturing industries and it is a glass rod where the optical fiber is drawn from. The preform can be regarded as a large-scale optical fiber with the same refractive index and waveguide structure as the drawn optical fiber. Usually optical fiber preform has the diameter in the range of 20−300 mm and length of 1 m while the conventional optical fiber has the diameter of 125 μm. By the mass conservation law, the lengths of optical fiber that can be drawn from one preform will depend on its volume, or equivalently its diameter and length, and there have been significant achievements in producing large volume optical fiber preform. We will briefly review the fundamental aspects of preform fabrication in terms of chemical process and dopant types.
In the fiber drawing process, glass fiber with a certain diameter, usually 125 μm, is continuously drawn from the neck-down zone of the preform that is formed by a high temperature ...