WHAT IS FIBRE OPTICS? USES OF FIBRE OPTICS ADVANTAGES DISADVANTAGES TECHNICAL WHAT IS FIBRE OPTICS? Fiber optics is the art of transmitting light and optical images through transparent fibers. The fibers, which generally are made of a glass or a clear plastic, can transmit light over a straight or curved path hundreds of feet long. The light transmission and flexibility of fiber optic lines are considerably superior to other components such as lenses, prisms, or mirrors. The basic principle of fiber optics has been understood since 1870, but major developments in this field have occurred primarily since 1951. Fiber optics is based upon the phenomenon of total internal reflection. The reflection is possible by transmitting laser-generated light waves through threadlike fibers of glass or plastic. The glass or plastic is spun to diameters between 5 and 100 micrometers. Once the desired diameter is achieved, the threads are packed into bundles of several thousand each. Because these bundles maintain some of the flexibility of the individual fibers, they can be twisted and bent to conduct light and images around corners. In order to protect the fibers and bond them together, they are coated with a thin layer of another material. The coating material must have a lower index of refraction and is usually a different type of glass or plastic. The technology used for drawing and assembling coated fibers is both fascinating and unique. For example, a glass-coated glass fiber is drawn by hanging a high refractive index glass rod within a low refractive index glass tube. The rod-tube assembly is then placed in a cylindrical furnace. The rod and tube will soften and eventually fuse together creating a fiber with a low refractive index coating. Fibers can be drawn by this process and then assembled into a bundle. It is important to understand why light is used as the means of transmitting information. When a transmitter sends a signal through a fiber optic line, that signal is carried on a beam of light. Light travels in waves and the number of waves that leave the transmitter per second is the frequency. Therefore the higher the frequency, the more information carried. Since light waves have such a high frequency, they can carry thousands of times more information than radio waves or current flowing in a wire. Back to Top Back to Home Page USES OF FIBRE OPTICS Optical fibers have long been used in medical instruments. Inserted into the body, they transmit the image of an organ or a lesion to a camera outside. This eliminates the need for exploratory surgery. Optical fibers can also link computers, robots, televisions, and telephones in many factories and offices. Such fibers, however, are not nearly transparent enough for telecommunication purposes. Light in a communication cables must travel for long distances without interference. Flaws, impurities, or bubbles in a fiber would absorb or reflect the tiny beam of light that must pass through the cable. Transmission losses in fibers have already been reduced to less than ten percent per kilometre. Optical fibers used for telecommunications must be welded together so as to be as nearly seamless as possible. The light generating devices used in telecommunication must be attached with great precision to the ends of the fiber. Optical fiber cables for long distance telephone service are in operation in the United States, Japan, France and Great Britain. Back to Top Back to Home Page ADVANTAGES Optical fiber cables have many advantages over copper cables. Their greater capacity for information means that smaller cables can be used. An optical fiber cable the size of an ordinary electrical cord can replace a copper cable hundreds of times thicker. The telephone cable vaults running under many city streets over the world are already filled. Optical fiber cables will allow more telephones lines. One major advantage of optical fibers is the low cost of the materials used in production. Glass is basically silicon which is the second most abundant material in the earth's crust. On the other hand copper is becoming increasingly scarce and expensive. Copper cables can suffer from static, which interferes with telephone and other communication lines. Because optical fibers carry light beams, they are free of electrical noise and interference. It obvious that fiber optic cables have many advantages over copper cables. The use of fiber optics is growing as the research for it continues to find more applications. The future market for fiber optic communications is immense and soon copper cables will be obsolete. Optical fiber can carry a lot more information. Two strands of optical fiber can carry 24,000 telephone calls. It would take approximately 48,000 copper wires to make the same number of phone calls. Fiber optic technology will make it possible to improve communication systems like the telephone by allowing people to actually see the person they are talking to. When fiber optic technology was first created it used multimode fiber. Multimode fiber allows the light to take several different paths down the glass fiber. This forces the signals to reach the end of the fiber line at different times. The end result was that images looked like ghosts. To help resolve some of these problems, engineers created single mode fiber. Single mode fiber allows the light to follow only one path. The single mode fiber eliminates the ghosting effect. Optical fibres carry signals with much less energy loss than copper cable and with a much higher bandwidth . This means that fibres can carry more channels of information over longer distances and with fewer repeaters required. Size and Weight Optical fibre cables are much lighter and thinner than copper cables with the same bandwidth. This means that much less space is required in underground cabling ducts. Also they are easier for installation engineers to handle. Security Optical fibres are much more difficult to tap information ; a great advantage for banks and security installations. They are immune to Electromagnetic interference from radio signals, car ignition systems, lightning etc. They can be routed safely through explosive or flammable atmospheres, for example, in the petrochemical industries or munitions sites, without any risk of ignition. Back to Top Back to Home Page DISADVANTAGES Disadvantages Price In spite of the fact that the raw material for making optical fibres, sand, is abundant and cheap, optical fibres are still more expensive per metre than copper. Having said this, one fibre can carry many more signals than a single copper cable and the large transmission distances mean that fewer expensive repeaters are required. Special Skills Optical fibres cannot be joined (spliced) together as a easily as copper cable and requires additional training of personnel and expensive precision splicing and measurement equipment. Running Costs The main consideration in choosing fibre when installing domestic cable TV networks is the electric bill. Although copper coaxial cable can handle the bandwidth requirement over the short distances of a housing scheme, a copper system consumes far more electrical power than fibre, simply to carry the signals. Back to Top Back to Home Page [GO TO APPLICATIONS PAGE] [GO TO PHYSICS PAGE] [GO TO FUTURE PAGE]