Drawing Fibers from the Preform Blank

Drawing Fibers from the Preform Blank
Once the preform blank has been tested, it gets loaded into a fiber drawing tower.

The blank gets lowered into a graphite furnace (3,452 to 3,992 degrees Fahrenheit or 1,900 to 2,200 degrees Celsius) and the tip gets melted until a molten glob falls down by gravity. As it drops, it cools and forms a thread.
The operator threads the strand through a series of coating cups (buffer coatings) and ultraviolet light curing ovens onto a tractor-controlled spool. The tractor mechanism slowly pulls the fiber from the heated preform blank and is precisely controlled by using a laser micrometer to measure the diameter of the fiber and feed the information back to the tractor mechanism. Fibers are pulled from the blank at a rate of 33 to 66 ft/s (10 to 20 m/s) and the finished product is wound onto the spool. It is not uncommon for spools to contain more than 1.4 miles (2.2 km) of optical fiber.

Testing the Finished Optical Fiber
The finished optical fiber is tested for the following:
Tensile strength - Must withstand 100,000 lb/in2 or more
Refractive index profile - Determine numerical aperture as well as screen for optical defects
Fiber geometry - Core diameter, cladding dimensions and coating diameter are uniform
Attenuation - Determine the extent that light signals of various wavelengths degrade over distance
Information carrying capacity (bandwidth) - Number of signals that can be carried at one time (multi-mode fibers)
Chromatic dispersion - Spread of various wavelengths of light through the core (important for bandwidth)
Operating temperature/humidity range
Temperature dependence of attenuation
Ability to conduct light underwater - Important for undersea cables
Once the fibers have passed the quality control, they are sold to telephone companies, cable companies and network providers. Many companies are currently replacing their old copper-wire-based systems with new fiber-optic-based systems to improve speed, capacity and clarity.