A transmitter terminal in an ultra-long haul optical transmission system receives separate channel input signals in separate ones of a plurality of return-to-zero transmitters (RZTX). Each RZTX generates a corresponding forward error correction (FEC) modulated output signal in a separate channel frequency...http://www.google.de/patents/US6731877?utm_source=gb-gplus-sharePatent US6731877 - High capacity ultra-long haul dispersion and nonlinearity managed lightwave communication systems
