20-gb/s quaternary intensity modulation based on duobinary modulation with unequal amplitude in two polarizations

Two 10-Gb/s duobinary data streams are combined with unequal amplitudes and two orthogonal polarizations to generate a narrowband 20-Gb/s (10-Gbaud) quaternary intensity modulation. Sensitivity and chromatic dispersion tolerance of this modulation format, measured with a pseudorandom binary sequence 2/sup 7/-1, are -18.6 dBm and 530 ps/nm, respectively.