HOW ARE OPTICAL FIBERS MADE?

The ability to communicate information is essential to achieve the successful advancement of humankind. Transmission of information is imperative to the expansion of our horizons. But how are optical fibers made? The article will discuss the basis of fiber optics in terms of its definition and manufacturing technology.

What is fiber optics?

In 1952, Narinder Singh Kapany who is an OCI American has invented optical fiber. After then optical fiber came into people's view. It is a transmission medium commonly used in data networks. A very fine thread of transparent material, glass, or plastic materials.

How are optical fibers made?

Optical fibers are made of very pure glass. The glass core or center is made of silica and is purified to minimize the loss of signal. It then gets coated to protect the fibers and to contain the light signals. The light signals carried by the optical cable consist of electrical signals that have been converted or changed into light energy.

The following process is followed to manufacture the optical fibers:

Step one: The Manufacturing of the Preform Blank

The silica must first be purified before it can be spun into glass fibers. This process takes a long time and the silica is heated to very high temperatures and then distilled to purification. The sand is heated to a temperature that will change the silica into a gaseous state. The silica will then be combined with other materials called dopants, which will react with the silica (in its gaseous state) to form the fibers. All the solid impurities are removed and the gas is cooled to form the fiber material.

A process called modified chemical vapor deposition (MCVD) is used to change the glass into the preform blank. During this process oxygen is bubbled through solutions of silicon chloride (SiCl4), germanium chloride (GeCl4) and other chemicals. The gas vapors are channeled to the inside of a synthetic silica quartz tube in a special lathe to form the cladding. While the lathe rotates a burning flame is moved back and forth on the outside of the tube.

The lathe turns continuously to allow the preform blank to be coated evenly. To maintain the purity of the glass a corrosion resistant plastic is used to accurately control the flow and the structure of the mixture. This process of manufacturing the preform blank takes a couple of hours. The preform blank is cooled and is inspected for quality through an inspection and control process.

Step two: Drawing fibers from the Preform Blank

After testing the preform, it is placed into a fiber “drawing tower.” The preform blank gets lowered into a furnace and is heated between 1,900°C to 2,200°C until the tip starts to melt and a molten blob starts to fall down. As it drops down, it cools and forms a strand. This strand is pulled through a sequence of coating cups (buffer applicators) and curing ovens using ultraviolet light, and then coiled onto a tractor-controlled reel. This process is accurately controlled using a laser micrometer to measure the thickness of the fiber. This information is then sent back to the tractor mechanism. The tractor mechanism pulls the fibers at a rate of 10 to 20m/sec and the finished product is wound onto a spool. A spool can contain more than 2,2km of optical fiber

Step three: Testing the Finished Optical Fiber

Once the optical fiber is manufactured it goes through a process of testing. The following tests are done:

• Tensile strength – The fibers must withstand 100,000 lb/in2 or more

• Refractive index profile – Determine that the core diameter, cladding dimensions and coating diameter are uniform. Screen also for optical defects.

• Attenuation – Determine the extent that light signals of various wavelengths degrade or reduce over certain distances.

• Information carrying capacity (bandwidth) – the number of signals that can be carried at one time (multi-mode fibers)

• Chromatic dispersion – Spread of various wavelengths of light through the core, this is very important for bandwidth.

• Operating temperature/humidity range – Determines the temperature and humidity that the fiber can withstand.

• Ability to conduct light underwater – critical for undersea cables

Once the fibers have passed the quality control process, they are sold to telephone companies, cable companies and network providers. Currently more and more companies are replacing their old copper-wire-based systems with new fiber-optic-based systems to improve speed, capacity and clarity.