Chapter 3: Preform manufacture and fiber drawing Production of silica glass through deposition Melting of ultrapure glass with furnace heated by radio frequency (RF) induction. Flowchart of the production of ultrapure silicon dioxide from natural quartz or quartz mineral sands. Deposition of silicon dioxide at high temperature in an ultrapure quartz tube in the MCVD (Modified Chemical Vapor Deposition) process. Modified Chemical Vapor Deposition (MCVD) Process description MCVD – deposition at Acreo Fiber Lab in Hudiksvall Sweden. Process description The MCVD – process. Collapse of the preform Intense heating causes the hollow preform to soften and collapse to a solid rod. Outside Vapor Deposition (OVD) Process description: phase 1 - deposition The OVD method for making a preform. Process description: phase 2 - the sintering process The porous preform is collapsed into a solid glass rod. Process description: phase 3 – fiber drawing Fiber drawing. Vapor-Phase Axial Deposition (VAD) Production process Schematic diagram showing the VAD method of preform manufacture. Fiber drawing Fiber drawing – principle drawing. Fiber drawing Fiber drawing - top of the tower. Typical primary coated single-mode fiber.