The DC may be likely for old-style repeaters, as Er-doped fiber amplifiers are (relatively) new.
It's my understanding that the pumping laser would be a different wavelength carried by the same fiber (just as a fiber can carry multiple data channels using different wavelengths in DWDM). The boost happens because of the special doped section.
The pumping laser essentially puts the doped medium in an energy condition where the data transmission can stimulate additional emission (similar to how lasers work in the first place). Few photons in, many out. The energy required to do so comes from the pumping laser.
It's my understanding that the pumping laser would be a different wavelength carried by the same fiber (just as a fiber can carry multiple data channels using different wavelengths in DWDM). The boost happens because of the special doped section.
Laser pumping is used extensively in laser physics, at places like the NIF: https://lasers.llnl.gov/about/nif/how_nif_works/injection_la...
The pumping laser essentially puts the doped medium in an energy condition where the data transmission can stimulate additional emission (similar to how lasers work in the first place). Few photons in, many out. The energy required to do so comes from the pumping laser.
http://en.wikipedia.org/wiki/Laser_pumping