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Fiber-Optic Technology

3. Outside Vapor Deposition (OVD) Process

Basic OVD optical fiber manufacturing consists of three steps: laydown, consolidation, and draw.


In the laydown step, a soot preform is made from ultrapure vapors as they travel through a traversing burner and react in the flame to form fine soot particles of silica and germania (see Figure 4).

Figure 4. OVD Laydown Process

The OVD process is distinguished by the method of depositing the soot. These particles are deposited on the surface of a rotating target rod. The core material is deposited first, followed by the pure silica cladding. As both core and cladding raw materials are vapor-deposited, the entire preform becomes totally synthetic and extremely pure.

When deposition is complete, the bait rod is removed from the center of the porous preform, and the preform is placed into a consolidation furnace. During the consolidation process, the water vapor is removed from the preform. This high-temperature consolidation step sinters the preform into a solid, dense, and transparent glass.
The Draw
The finished glass preform is then placed on a draw tower and drawn into one continuous strand of glass fiber (see Figure 5).

Figure 5. Optical Fiber Drawing Process

First, the glass blank is lowered into the top of the draw furnace. The tip of the blank is heated until a piece of molten glass, called a gob, begins to fall from the blankómuch like hot taffy. As the glob falls it pulls behind it a thin strand of glass, the beginning of an optical fiber.

The gob is cut off, and the fine fiber strand is threaded into a computer-controlled tractor assembly and drawn. Then, as the diameter is monitored, the assembly speeds up or slows down to precisely control the size of the fiberís diameter.

The fiber progresses through a diameter sensor that measures the diameter hundreds of times per second to ensure specified outside diameter. Next, the inner and outer primary coatings are applied and cured, using ultraviolet lamps. At the bottom of the draw, the fiber is wound on spools for further processing.

Fiber from these spools is proof-tested and then measured for performance of relevant optical and geometrical parameters. Each fiber has a unique identification number that can be traced to all relevant manufacturing data (including raw materials and manufacturing equipment). Each fiber reel is then placed into protective shipping containers and prepared for shipment to customers worldwide.

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