As for long-haul networks, they continue to evolve to higher bit rates and longer distances. Ultra, available fourth quarter 2001, supports the newest technological advances, like distributed Raman amplification, thereby significantly extending the reach of optical transmission and reducing the costs associated with regeneration of the optical signal. Usage of Raman amplification today in long-haul networks is in its infancy but is forecasted to grow aggressively over the next few years. Ultra is the only fiber to guarantee low attenuation in the 1450nm wavelength transmission window, where Raman amplification is used. Advanced fibers have been aggressively deployed globally over the last few years.
Dispersion is a property of fiber that causes light pulses to spread.
This effect limits the bit-rate and the distances that can be bridged over the fiber. Therefore, systems designers use special devices called dispersion compensating modules that compensate for this effect. The most commonly used transmission band for DWDM is the C band, centered on the 1550nm wavelength. Many short length metro systems are centered on the 1310nm wavelength. For Raman amplification, systems designers will use laser pumps in the 1450nm wavelength window to boost the transmission signal in the C band.