Highly dispersed pulses for transmission at 40 Gb/s

As the signal-to-noise ratio (SNR) requirement increases, there is a need for higher launched signal power, which can increase signal degradation from fiber nonlinearities, such as self-phase modulation (SPM). However, short pulse RZ offers significant advantages for transmission at 40 Gb/s. The broad spectrum of the short pulses leads to a very short dispersion length in dispersive fibers, such as standard single-mode fibers (SMF) operating around 1550 nm. Because the pulses become highly dispersed, phase-matching of the frequency components in the signal is reduced in the fiber link, which reduces the effects of SPM. Therefore, the launched signal power can be increased to provide sufficient SNR for transmission over many amplified spans. Moreover, once the pulses are dispersed, the location of dispersion compensation is not critical. Therefore, all dispersion compensation can be placed at the end of the transmission link, rather than in the more usual span-by-span configuration. Using these concepts, we demonstrate 40 Gb/s transmission over SMF links up to 800 km.