Optical transport systems vendor Ciena Corp. (NYSE: CIEN) says it has complemented its terrestrial trials of 200-Gbps optical transmission via 16-QAM with an undersea cable network test. The company partnered with the Japan-U.S. Cable Network to transmit 200G signals over a 630-km submarine network segment along the U.S. West Coast.
The optical transport community has focused on 16-QAM optical modulation as a means of transmitting 400 Gbps via coherent transmission, usually via a pair of 200-Gbps subcarriers. Some network operators have expressed interest in using just one of the subcarriers to double the data rate of 100-Gbps links as an interim step towards 400G. Verizon has tested just such a capability with Ciena over part of its terrestrial network in the U.S. Northeast (see “Verizon tests 200-Gbps in the field”).
The trial with the Japan-U.S. Cable Network illustrates that the concept could also work on at least some submarine cable links. As was the case with the Verizon trial, this demonstration used Ciena’s 6500 Packet Optical platform equipped with WaveLogic coherent optical processors. The submarine network – managed by 35 consortium members, including CenturyLink, KDDI, NTT Communications, SoftBank Telecom, and Verizon – already uses the 6500 packet optical transport system to support 100-Gbps transmission rates (see “Ciena to upgrade Japan-US Cable trans-Pacific network with 100G”).
“The Japan-U.S. Cable Network is a critical source of capacity for our consortium members,” said Masahiro Soma, Japan-US CN management committee chairman/upgrade procurement group co-chairman. “The goal of this trial was to ensure that the cable’s various segments can be equipped with appropriate future-proof technologies to scale network capacity in a cost-effective manner, as needed to meet rapidly increasing demand for bandwidth. This collaboration with Ciena is helping the network prepare for cost-effective growth.”
“Thanks to a combination of high-performing coherent optics and compelling economics, Ciena’s submarine solutions are well-suited to address the global push for higher-capacity submarine links – well beyond 100G. With our WaveLogic technology powering several complex submarine cable systems across some of the world’s most challenging geographies, a successful trial of this nature with Japan-U.S. Cable proves that we are ready to take these networks to the next level,” asserted Ed McCormack, vice president and general manager of Submarine Systems at Ciena.
However, questions remain about how broadly 16-QAM can be applied to submarine networks. The technology does provide more efficient transmission of signals greater than 100 Gbps than dual-polarization quadrature phase-shift keying (DP-QPSK), the modulation format most commonly used in today’s 100G coherent transmission systems. However, the improvement in data rates comes at the cost of a reduction in reach. It remains to be seen whether 16-QAM technology can be applied successfully to transoceanic links across the Atlantic or Pacific.
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