The basic structure for creating a glass preform cylinder used in the mass production of glass optical fiber.The process begins with heating silica and germanium to the point that it vaporizes.The glass vapor cools and is deposited as layers of soot on the outside of a rotating hollow bait rod, also known as a seed rod.When the deposition process is complete, the bait rod is removed and the remaining glass cylinder is collapsed. See also outside vapor deposition (OVD).