Fiber- Optic
Fiber optic cables utilize light waves to transmit data through a thin glass or plastic fiber. The structure of a typical fiber optic cable is shown in the diagram. The parts of the cable are as follows:
The light conductor is a very fine fiber core. Glass is the most common material, allowing signals to be transmitted for several kilometers without being refreshed. Plastic is used in some circumstances, but plastic cables allow only short cable runs.
The cladding is a glass layer that surrounds the optical fiber core. The optical characteristics of the cladding reflect light back to the core, ensuring that little of the light signal is lost.
A sheath or jacket protects the cable from damage. A single sheath can be used to bundle multiple core/cladding fibers into a multi-fiber cable.
The light signals on fiber optic cables are generated either by light emitting diodes (LEDs) or by injection laser diodes (ILDs), which are similar to LEDs but produce laser light. The purity of laser light is desirable, increasing both data rates and transmission distance. Signals are received by photodiodes, solid state devices that detect variations in light intensity.
The interface devices required to operate with fiber optic cable are more expensive than those required for copper cable. The higher cost is the result of several factors, including cost of the components and tighter design characteristics because fiber optic cables generally are operated at high data rates. The cost of fiber optic cable installation, however, is trending downward.
Fiber optic cables have many desirable characteristics. Because the fibers are small in diameter, a cable of a given size can contain more fibers than copper wire pairs. Because fiber optic cables use light pulses instead of electrical signals, they offer very high bandwidth. Bandwiths of 100 megabits (million bits per second) are commonplace, and bandwidths in the gigabit (billion bit) per second range are available.
Because the signal in a fiber optic cable consists of light pulses, the signal cannot be affected by electromagnetic interference. Nor can the cables radiate radio frequency noise. Optical fibers are, therefore, suitable for use in the noisiest and most sensitive environments. Because these cables radiate no electromagnetic energy, it is impossible to intercept the data signal with electronic eavesdropping equipment. Fiber optic transmissions are extremely secure.
Installation of fiber optic cable requires greater skill than is necessary to install most copper cables. Cables must not be bent too sharply, and connectors must be installed by skilled technicians using special tools. However, new connector technologies have simplified installation and reduced cost.
Here are some advantages of fiber optic cable:
Very high bandwidth.
Immunity to EMI; fiber optic cables can be used in environments that make wire cables unusable.
No radio frequency emissions; signals on fiber optic cables cannot interfere with nearby electronic devices and cannot be detected by conventional electronic eavesdropping techniques.