A cable is most often two or more wires running side by side and bonded, twisted, or braided together to form a single assembly, but can also refer to a heavy strong rope. In mechanics, cables, otherwise known as wire ropes, are used for lifting, hauling, and towing or conveying force through tension. In electrical engineering cables are used to carry electric currents. An optical cable contains one or more optical fibers in a protective jacket that supports the fibers.
A coaxial cable is a specific type of cable
that consists of four layers of material. There is an inner conductor, a
dielectric insulating layer, another conductive layer, and an
insulating layer. The cable is called coaxial because both
the inner and outer conductive layers are on the same geometric axis. A
geometric axis is a line passing through the length of the material.
Fiber-optics, also called optical fiber, is a technology that allows light to travel along thin glass or plastic wires. These wires are typically bundled into fiber-optic cables. This type of cable is used most commonly in the communications industry, because digital information can be converted into light pulses that move along the length of the wires. The cables vary in length, from a few feet to long enough to cross continents or oceans.
Telephone calls, the Internet, and cable television are examples of the kinds of information that can pass through a fiber-optic cable. It is typically less expensive than copper wiring. These cables may run to homes and businesses, but they are typically used for long distance communication. It has not been known to turn corners easily without losing signal strength, however, so it is used more often for straight, level distances.
Many individuals in the communications industries prefer fiber-optics to copper wiring. First and foremost, fiber-optics typically offer better bandwidth, meaning they can carry more information at once. Secondly, there is usually less attenuation, or signal degradation, in a fiber-optic cable. Thirdly, whereas copper wires use electrical signals, fibers use light waves, so there is less chance of interference in the signal. Lastly, optical fiber wires are made of glass, so there is little risk of fire.
A fiber-optic cable is made up of many fiber-optic wires all bundled together. The major component in each wire is the optical glass or plastic core. This core is a thread of clear material that must be as pure as possible in order to conduct light over long distances. Impurities in the core may cause a degradation in the signal.
Any fiber-optic cable uses a process called total internal reflection to transmit information down its bundled wires. This particular type of reflection occurs when light hits a clear surface at a precise angle and bounces back instead of penetrating it. An example of total internal reflection occurring in nature can be seen when a swimmer is just barely underwater and he or she can see the ocean floor reflected in the undersurface of the water. This reflection occurs due to the angle of the swimmer in relation to the water’s surface.
The light pulse within a fiber-optic cable hits the outer walls of the wire at a similar angle, which keeps the light wave moving forward. The outer surface of the glass wire provides just the right angle of reflection to keep the light bouncing back and forth along the length of cable. The core is encased in cladding, which is an optically-reflective material that aids in this process.
Light signals typically enter the fiber-optic cable at one end and are received at the other. The signals are usually converted from digital or voice information by a computer. They are then emitted into the cable in the form of light pulses made by a laser or a light-emitting diode (LED) through a lens.