Fiber Optic Wiki

What is erbium amplifier?

June 7, 2011

An erbium amplifier, also called optical amplifier or an erbium-doped fiber amplifier or EDFA, is an optical or IR repeater that amplifies a modulated laser beam directly, without opto-electronic and electro-optical conversion. The device uses a short length of optical fiber doped with the rare-earth element erbium. When the signal-carrying laser beams pass through this fiber, external energy is applied, usually at IR wavelengths. This so-called pumping excites the atoms in the erbium-doped section of optical fiber, increasing the intensity of the laser beams passing through. The beams emerging from the EDFA retain all of their original modulation characteristics, but are brighter than the input beams.

Optical Fiber Technology

June 7, 2011

Optical Fiber is a technology that uses glass (or plastic) threads (fibers) to transmit data. The operation of an optical fibre is based on the principle of total internal reflection. Light reflects or refracts, depending on the angle at which it strikes a surface. A fiber optic system is similar to the copper wire system. The difference is that fiber-optics use light pulses to transmit information down fiber lines instead of using electronic pulses to transmit information down copper lines. Looking at the components in a fiber-optic chain will give a better understanding of how the system works in conjunction with wire based systems.

Bandwidth-distance product

June 6, 2011

Because the effect of dispersion increases with the length of the fiber, a fiber transmission system is often characterized by its bandwidth-distance product, often expressed in units of MHz×km. This value is a product of bandwidth and distance because there is a trade off between the bandwidth of the signal and the distance it can be carried. For example, a common multimode fiber with bandwidth-distance product of 500 MHz×km could carry a 500 MHz signal for 1 km or a 1000 MHz signal for 0.5 km.

Dispersion

June 6, 2011

For modern glass optical fiber, the maximum transmission distance is limited not by direct material absorption but by several types of dispersion, or spreading of optical pulses as they travel along the fiber. Dispersion in optical fibers is caused by a variety of factors. Intermodal dispersion, caused by the different axial speeds of different transverse modes, limits the performance of multi-mode fiber. Because single-mode fiber supports only one transverse mode, intermodal dispersion is eliminated.

Regeneration

June 6, 2011

When a communications link must span a larger distance than existing fiber-optic technology is capable of, the signal must be regenerated at intermediate points in the link by repeaters. Repeaters add substantial cost to a communication system, and so system designers attempt to minimize their use.

Last mile

June 6, 2011

Although fiber-optic systems excel in high-bandwidth applications, optical fiber has been slow to achieve its goal of fiber to the premises or to solve the last mile problem. However, as bandwidth demand increases, more and more progress towards this goal can be observed. In Japan, for instance EPON has largely replaced DSL as a broadband Internet source. South Korea’s KT also provides a service called FTTH (Fiber To The Home), which provides 100 percent fiber-optic connections to the subscriber’s home. The largest FTTH deployments are in Japan, Korea, and recently in China. Singapore has also started implementation of their all-fibre Next Generation Nationwide Broadband Network (Next Gen NBN), which is slated for completion in 2012 and is being installed by OpenNet. Since they began rolling out services in September 2010, Network coverage in Singapore has since reached 60% nationwide.

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