Infinera, Telstra send PM-8QAM across submarine network

Optical transport systems developer Infinera and Australia-based service provider Telstra say they have successfully transmitted polarization-multiplexed 8 quadrature amplitude modulation (PM-8QAM) signals across 2,200 km of Segment F of the Reach North Asia Loop (RNAL) submarine cable network.

Segment F of the RNAL submarine network runs between Wada in Japan and Pusan in South Korea. The superchannel technology transmission leveraged Infinera's FlexCoherent modulation formats, along with advanced transmitter and receiver-based signal processing technologies. These techniques included coherent transmitter-based Nyquist DWDM pulse shaping and both transmitter and receiver-based non-linear compensation technologies.

The parties described PM-8QAM as the next step in coherent transmission for undersea cable networks. It offers a 50% increase in capacity versus the PM-QPSK coherent modulation format typically used today to support 100-Gbps transmission rates, the two companies say.

"This trial demonstrates the potential of a full suite of FlexCoherent modulation formats on a single line card and the ability to precisely trade capacity for reach and margin," said Steve Grubb, Infinera Fellow and the architect behind the RNAL demonstrations. "It also highlights the emergence of next-generation coherent processing that works with existing coherent 100-Gbps technologies, which are now firmly entrenched in modern submarine terminating line equipment."

The PM-8QAM demonstration was part of a larger showcase of submarine superchannel capabilities Telstra and Infinera conducted. The showcase also featured transmission of signals based on PM-3QAM modulation over a 4,250-km link between California and Hawaii.

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