How optical fiber is made
Three methods are used today to fabricate moderate-to-low loss waveguide fibers: Modified Chemical Vapor Deposition (MCVD), Outside Vapor Deposition(OVD), and Vapor Axial Deposition (VAD).
Modified Chemical Vapor Deposition (MCVD)
In MCVD a hollow glass tube, approximately 3 feet long and 1 inch in diameter (1 m long by 2.5 cm diameter), is placed in a horizontal or vertical lathe and spun rapidly. A computer-controlled mixture of gases is passed through the inside of the tube. On the outside of the tube, a heat source (oxygen/hydrogen torch) passes up and down as illustrated in the following figure.
Each pass of the heat source fuses a small amount of the precipitated gas mixture to the surface of the tube. Most of the gas is vaporized silicon dioxide (glass), but there are carefully controlled remounts of impurities (dopants) that cause changes in the index of refraction of the glass. As the torch moves and the preform spins, a layer of glass is formed inside the hollow preform. The dopant (mixture of gases) can be changed for each layer so that the index may be varied across the diameter.

After sufficient layers are built up, the tube is collapsed into a solid glass rod referred to as a preform. It is now a scale model of the desired fiber, but much
shorter and thicker. The preform is then taken to the drawing tower, where it is pulled into a length of fiber up to 10 kilometers long.
Outside Vapor Deposition (OVD)
The OVD method utilizes a glass target rod that is placed in a chamber and spun rapidly on a lathe. A computer-controlled mixture of gases is then passed between the target rod and the heat source as illustrated in the figure below. On each pass of the heat source, a small amount of the gas reacts and fuses to the outer surface of the rod. After enough layers are built up, the target rod is removed and the remaining soot preform is collapsed into a solid rod. The preform is then taken to the tower and pulled into fiber.
Vapor Axial Deposition (VAD)
The VAD process utilizes a very short glass target rod suspended by one end. A computer-controlled mixture of gases is applied between the end of the rod and the heat source as shown in the figure below. The heat source is slowly backed off as the preform lengthens due to tile soot buildup caused by gases reacting to the heat and fusing to the end of the rod. After sufficient length is formed, the target rod is removed from the end, leaving the soot preform. The preform is then taken to the drawing tower to be heated and pulled into the required fiber length.
Draw Optical Fiber from the Preform
In this step, the finished glass preform is installed at the top of a tower which supports various devices used in the fiber drawing process.

The process begins by lowering one end of the preform into an in-line furnace that produces heat in a range of 3,400 to 4,000 degrees Fahrenheit. As the lower end of the preform begins to melt, it forms a molten glob that is pulled downward by gravity. Trailing behind the glob is a thin strand of glass that cools and solidifies quickly.

The equipment operator threads this glass strand through the remainder of the devices on the tower, which include a number of buffer coating applicators and ultraviolet curing ovens. Finally, the operator connects the fiber to a tractor mechanism.

The tractor device pulls the glass strand from the preform at a rate of 33 to 66 feet per second. The actual speed at which the tractor pulls the strand is dependent upon the feedback information the device receives from a laser micrometer that continually measures the fiber's diameter.

At the end of the run, the completed fiber is wound onto a spool.