Q. Wire-line and Fiber-optic channel?

Wire-line channels are used extensively by the telephone network for voice, data, and video transmission. Twisted-pair wire lines (with a bandwidth of several hundred kHz) and coaxial cable (with a usable bandwidth of several MHz) are basically guided electromagnetic channels.

Fiber-optic channels offer a channel bandwidth that is several orders ofmagnitude larger than coaxial cable channels. The transmitter or modulator in a fiber-optic communication system is a light source, such as a light-emitting diode (LED) or a laser, whose intensity is varied (modulated) with the message signal. The light propagates through the fiber as a light wave and is amplified periodically along the transmission path to compensate for signal attenuation. At the receiver end, the light intensity is detected by a photodiode, whose output is an electric signal that varies in direct proportion to the power of light striking on the photodiode. Optical fiber channels are replacing nearly all wire-line channels in the telephone network.