As a result, efforts are continuously being made to increase the bit-rate capacity and transmission reach of submarine cable systems, which support more than 99% of trans-oceanic data traffic.
With 100Gb/s technologies now commercially deployed, the focus of recent development is turning to high capacity channels, beyond 100Gb/s, with more efficient bandwidth utilization. As part of this movement, NEC has proposed optical superchannels to increase fiber capacity in both terrestrial and submarine networks. Optical superchannels are based on advanced technologies such as parallel high-speed transceivers, advanced modulation formats and advanced pulse shaping. Superchannels constitute a practical platform for next-generation submarine systems specifically designed to help carriers to significantly increase transmission capacity in a cost efficient, scalable and flexible manner.
As a result of these proposals, NEC successfully tested a 1Tb/s superchannel for submarine ultra-long haul systems that uses the latest optical and digital technologies to provide traffic management flexibility and improve transmission performance over ultra-long haul transmission distances. Results from this real-time operation with error-free performance were presented at the Asia Communications and Photonics Conference in Shanghai in November 2012.
Key technologies of the 1Tb/s superchannel are as follows:
a) NEC combined a software-defined pulse shaper together with flexible-grid real-time 100Gb/s subcarriers to create a 1Tb/s superchannel. The pulse-shaper is designed to mitigate transmission impairments and to offer flexible bandwidth allocation capabilities. NEC achieved error-free transmission over a 5,400km link consisting of commercially available optical fiber and cost-effective repeater spacing. This technology provides a 43% improvement over the bandwidth utilization of current commercial systems.
b) NEC also implemented a 1Tb/s superchannel composed of full-digital 100Gb/s subcarriers. Each subcarrier is equipped with a digital signal processor at the transmitter, which can potentially extend the re-configurability to a variable modulation format and/or for variable error-correction capabilities. This cutting-edge digital-transmitter technology enables the 1Tb/s superchannel to successfully transmit beyond 7,200-km.
