The DWDM line with long spans
Increasing the span length using optical amplifying
Optical amplifiers allow increasing the span length due to increasing the signal power during transmission and the sensitivity during receiving.
The most cost-efficient solutions are those with erbium amplifiers (EDFA). The simultaneous use of a power amplifier and a preamplifier allows transmission of 16 optical channels for a distance up to 220 km and 40 channel for a distance up to 200 km.
The use of Raman amplifier units in addition to EDFA transmission and receiving amplifiers allows organizing transmission of optical channels for a span length up to 250–350 km in systems with up to 16 optical channels.
With the 250 km span it’s possible to transmit 40.
Extra-long sections of a DWDM line. The ROPA technology (remote optical pumped amplifier) is used for remote pumping of the fiber alloyed with erbium (EDF). Amplifiers are pumped via a separate fiber.