“Bell Labs , which has made a hobby out of 100Gbps Ethernet lately, has presented lab results that claim serial 100Gbps transmission across a 2,000km distance. Lucent divulged the results in a paper titled, “2,000-km WDM Transmission of 10 x 107Gbps RZ-DQPSK.”
Light Reading - Lucent - Lucent Stretches 100-GigE - Telecom News AnalysisThe 2000 km span was repeatered every 80 to 100 km using Raman amplifiers and the components used were normal 40Gbps components commercially available today. RZ-DQPSK modulation was used so that 100Gbps signal was actually being transmitted at 50Gbps. With DQPSK, 2 bits are transmitted with each symbol.