Thursday, March 13, 2008
Tuesday, March 11, 2008
Optical Networks
Communications between computers, telephones and other electronic devices using light is known as Optical Networking. An optical network is far more reliable and has far greater potential transmission capacity than networking in the electrical domain. Optical networks are the communication networks that are build using communication media like Optical Fibers, and transfer of data using fiber-optic and light is known as fiber-optic communication. Fiber-optic communication is a method of transmitting information from one place to another by sending light through an optical fiber. An optical fiber (or fiber) is a glass or plastic fiber designed to guide light along its length. Fibers are used instead of metal wires because signals travel along them with less loss, and they are immune to electromagnetic interference. Light is kept in the "core" of the optical fiber by “total internal reflection”. Fibers which support many propagation paths or transverse modes are called multimode fibers (MMF). Fibers which support only a single mode are called single mode fibers (SMF). Multimode fibers generally have a large-diameter core, and are used for short-distance communication links or for applications where high power must be transmitted. Single mode fibers are used for most communication links longer than 200 meters.
The advantages of such type of communication with the help of such fiber are that the immunity to noise and interference is provided, the cost of transfer per unit bandwidth is reduced, and moreover the tapping of signal from fiber without being detected is extremely difficult.
In optical networks when the signals are transmitted they remain in optical form till its arrival at destination. For this purpose an all-optical fiber-optic switching device that maintains the signal as light from input to output is used. Optical switches direct the incoming bit stream to the output port no matter what the line speed or protocol is, and do not have to be upgraded for any such changes .Optical switches may separate signals at different wavelengths and direct them to different ports, using tiny mirrors that reflect the input signals to the output port, MEMS (Micro lector Mechanical Systems) technology is expected to be the prevailing method for building Optical switches.
To use the complete available bandwidth the technologies like W.D.M are used. Wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to enabling bidirectional communications over one strand of fiber. "This is a form of frequency division multiplexing (FDM) but is commonly called wavelength division multiplexing."