25 x 40-Gb/s copolarized DPSK transmission over 12 x 100-km NZDF with 50-GHz channel spacing

We report the first transmission of copolarized 40-Gb/s channels with 0.8-b/s/Hz spectral efficiency. We transmit 25 channels over 1200 km of nonzero-dispersion fiber (1600 km with adjacent channels orthogonally polarized). This result was obtained using differential phase-shift keying, and without forward error correction.