The growing demand for transmission capacity on optical fiber trunk lines has accelerated the research into Terabit/s long distance transmission [1]. We have already investigated the key technologies of 20 Gb/s based Terabit/s long distance transmission, such as, dispersion managed WDM soliton, precisely dispersion-flattened line, 1.55/1.58μm hybrid repeater amplifier and polarization interleave multiplexing. And using these technologies, we have achieved 1.1 Tb/s transmission over 3,020 km [2]. In this experiment, 55-channel, 20 Gb/s RZ signals with channel spacing of 0.8nm were packed into a 44nm optical bandwidth. In this paper, for the further capacity increase, we have expanded the flat gain bandwidth to 64nm by optimal gain equalization techniques, and used a narrow channel spacing of 0.4nm. Polarization maintaining AWG multiplexers have been developed for polarization interleave WDM transmitter to minimize the optical SNR degradation in the ultra-large-channel-number system. Using these technologies, we have achieved to transmit 3.2 Tb/s (160×20 Gb/s) signal over 1,500km.
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