The purity of

laser light makes lasers ideally suited

to data transmissions because they

can work with long distances and high

bandwidths. Lasers, however, are

expensive light sources used only

when their special characteristics are

required. Fiber optical transmission is using usually as a backbone for a big Lan networks, because the installation of optical cable is very hard and will not be effective or sometimes impossible to connect computers with optical cable between each other, because optical cable has a minimum bend radius. Optical cables are used when we need to transfer big amount of data such as real-time video processing. Another advantage of fiber optic is that there is not possible to eavesdropping because we don’t uses electrical signal.









Wireless transmission of signal.



In wireless transmission we don’t need to use physical medium such as copper or fiber optical cables so we don’t need to spend money for buying cables. In wireless transmission we use as a medium air. But here is one main problem because it is not much free electromagnetic spectrum. As a signal carier we can use a photon ( infra red) or an electric waves (radio, satellite). Four most common wireless transmission methods are :



Gamma Rays

X – Rays

Ultraviolent

--------------------------------- visible light

Terahertz Extremely High frequency

Super High frequency Microwave

Ultra High frequency

Gigahertz Very High frequency

High frequency

Medium frequency

Megahertz Low frequency Radio waves

Very Low frequency

Voice frequency AudioFreq 30Hz25kHZ

Kilohertz Extremely Low frequency









Infrared


Laser


Narrow band radio


Spread spectrum radio


Microwave












Infrared transmission: uses same principle as TV remote control.