FAQ6: Metro networks require low cost amplification solutions. What is the alternative to using the expensive wideband EDFAs found in long haul networks?

The best solution is to use narrowband EDFAs within a banded DWDM structure, so that not only the DWDM but also the amplifiers are scalable. A narrowband EDFA amplifies from 1 to eight 100 GHz spaced channels (as opposed to 40 for a Wideband EDFA) and is connected after a wideband WDM, which forms the upgrade port for other bands. This allows service providers to use only the capacity they need when they initially deploy networks, with the option of adding more channels over time as their revenues and usage increase.

The requirements for narrowband EDFA are relaxed compared to wideband EDFAs. A low power, cooler-less pump diode replaces the expensive high power lasers and the gain uniformity is tolerable in short wavelength range, making gain flattening filters (GFF) unnecessary. Following this configuration, Lightwaves2020 recently announced the availability of a $999 EDFA (in large volume) at OFC2002. This product dramatically reduces the overall cost of system amplification.

For more details related to metro network structure using narrowband EDFA, please refer to our article on it in WDM Solutions, July, 2002 issue.