Verfahren zur Herstellung einer grossen Vorform für einzelmode Fasern

摘要

A large optical preform Ä303Ü is made by a modified chemical vapor deposition (MCVD) process by depositing successive layers of core and cladding materials onto the inside surface of a rotating glass tube Ä33Ü having a hydroxyl ion (OH<->) level that is less than 0.5 parts per million (ppm) by weight. The tube is then collapsed inwardly to form a core rod Ä301Ü in which the deposited core material Ä31Ü has a diameter that is greater than about 5 millimeters and the deposited cladding material Ä32Ü has an outside diameter that is less than about 15 millimeters. Optionally a machine-vision system Ä140,150,160Ü monitors and controls the diameter of the glass tube by regulating the pressure within the tube; moreover, the machine-vision system monitors and controls the straightness of the tube by varying its rotational speed according to angular position. After the core rod Ä301Ü is formed, it may be plasma etched to remove contaminants, it is overclad with two glass jackets Ä34,35Ü having a hydroxyl ion (OH<->) level that is less than 1.0 ppm by weight thereby creating a large preform Ä303Ü from which about 400 kilometers of singlemode optical fiber can be drawn per meter of length of preform.