Impact of response flatness on duobinary transmission performance: an optimized transmitter with improved sensitivity

We study the effect of transmitter response amplitude and group delay ripples on the performance of systems using duobinary coding. We demonstrate an improved 10-Gb/s transmitter with very low required optical signal-to-noise ratio in back-to-back and transmission over about 4300 ps/nm (258 km of single-mode fiber at 1550 nm) with about 2-dB penalty (at bit-error rate BER=10/sup -3/).