Transmission of 8 x 20 Gb/s DQPSK signals over 310-km SMF with 0.8-b/s/Hz spectral efficiency

We report the transmission of eight-channel 20-Gb/s differential quadrature phase-shift-keying signals over 310-km conventional single-mode fiber. The high spectral efficiency (0.8 b/s/Hz) and successful transmission are achieved without using polarization multiplexing, Raman amplification, and forward error correction.