Researchers from Tokyo-based NEC Corp. reported at the European Community Optical Communication Conference in Munich, Germany, that they have demonstrated a transmission capacity of 6.4 Tb/s over a 186-km fiber. The team developed technologies to enable the transmission of 160 channels at 40 Gb/s. NEC will continue work to commercialize the system. The researchers used GaAs heterobipolar transistors to quadruple channel capacity, and a polarization interleave multiplexer and wavelength/polarization demultiplexer with automatic control over the polarization to double the spectral efficiency. They reduced polarization mode dispersion in the fiber and optical amplifiers to less than 0.8 ps.