Abstract
Lightguide fiber is drawn from a solid glass cylinder, or preform made by the MCVD process, in which layers of glass are built up on the inside of a tube by the reaction of glass precursor vapors, resulting in the formation of particles which deposit and are fused on the tube wall. The composition of the reactants is automatically controlled to give a graded index of refraction in the deposited layers. When a multimode fiber is drawn from the preform, the deposited glass becomes the lightguide core and the silica tube becomes the cladding. Preform manufacture is a critical part of lightguide manufacture, since it strongly influences bandwidth and attenuation of the fiber. Lightguide properties that are most strongly influenced by the preform and the materials and process used to make preforms are discussed.