OVD (Outside Vapor Deposition) A commonly used technique for the mass production of glass optical fiber, OVD begins with heating silica and germanium to the point of vaporization. As the glass vapor cools, it is deposited as layers of soot on the outside of a rotating hollow ceramic bait rod to create a glass cylinder. The first layer is the core material of germanium-doped silica. On top of the core material, many layers of slightly purer silica soot, i.e., silica with lower levels of dopants, are deposited to form the cladding. If the end product is to be a step-index fiber, there is an abrupt change in the chemical com- 74570c15.qxd 9/11/07 12:26 PM Page 355 |