extend your reach

A collaboration of researchers from British Telecommunications, Finisar in the USA, and Viavi Solutions in Germany report a successful field trail of a 400GBASE-LR8 optical transceiver. The experiment demonstrates the stable long-term error free performance of optical signals over fibre lengths up to 35 km; significantly longer than the IEEE standard of 10 km. The trail also demonstrates error free full throughput performance of the optical transceiver over a 27 km field link cable for the first time and indicates that the device is suitable for practical network deployment with potential for even greater cable reach. Optical fibre systems transport data and underpin the digital world experienced today. An optical transmission system comprises an optical transmitter, optical fibre, and an optical receiver. Optical fibres, as a transmission medium have low loss across a wide wavelength range and are ideal for transporting data across long distances. In an optical transmitter, optical signals, generated by a laser, are modulated by electronic data signals and then transmitted via optical fibre. At the end of the fibre transmission, the optical receiver detects and recovers the data. The team working in the laboratory and the experimental setup with the tester, optical transceiver, and fibres. The small CFP8 400GbE optical transceiver used in the experiments. Optical pluggable transceivers contain both an optical transmitter and receiver in a single housing, which are used as the client data interface between high-speed electronics and optical fibre transmission systems. Pluggable client transceivers are required to have optical reach in the range of hundreds of metres to tens of km. Significant advances in fibre transmission technologies have taken place in recent years, including key advances for achieving high data capacity over ultra-long distances. Optical ethernet client interface speeds have increased dramatically over recent years with the potential to reach terabit/s speeds in the future. To achieve IEEE standard speeds, new pluggable optical transceivers exploiting advanced modulation formats are being rapidly developed in the industry. In the team's Letter, they successfully demonstrate the application of these new techniques to achieve, for the first time, robust performance of 400GbE capable optics in a real-world environment. Author Yu Rong Zhou notes, “We successfully demonstrated operation over both laboratory and field installed fibres, showing the practical viability, and, the potential of the new IEEE 802.3bs 400GBASE-LR8 optical transceiver to achieve reaches well beyond its 10 km specification.” Doctor Zhou's BT technology team has worked together with Viavi Solutions, leaders in ethernet testing and measurement, and Finisar, industry leaders in high-speed optical pluggable transceivers to evaluate the performance limitations of new 400GbE pluggable optics. Trials of the latest pluggable optics, 400GBASE-LR8 defined for 10 km reach in IEEE standards, were performed and demonstrated, for the first time, real world performance of the new 400GbE technology in an operational network environment and have shown its viability for practical network application and potential for reach beyond its 10 km specification. These trials present great confidence that this emerging technology is robust and fit for deployment in future networks. A major challenge for the group was achieving longer reach while keeping the power and cost sufficiently low. To address these challenges, techniques such as advanced modulation (PAM4), advanced node CMOS ASIC and low cost Directly Modulated Lasers (DMLs) need to be employed and implemented in small size optical pluggables. For practical network application, the challenge was not only loss from field fibres but also the losses introduced from optical patch panels in operational exchanges. The enhanced performance resulting from the above techniques is shown to overcome these network losses. This early work demonstrates the practical viability of the new 400GbE optical client interfaces. The work demonstrates the robustness and practicality of the emerging technology, giving confidence to the industry that the technology works in a real world and demanding environment, giving operators the confidence to deploy as and when they need in the future. More specifically, the 400GBASE-LR8 extended to ∼30 km reach enables performance/cost not achieved previously in client optics. Regarding client interfaces, the next step for the team is size and cost reduction related to developing the form factor for improved performance benefits. Further field trials are planned to validate this improved technology. Also, client signals need to be mapped onto the optical line side of transmission systems such that traffic can be transmitted over longer, even global, reaches. To this end, their latest work will study the mapping of signals onto differing optical line side signal formats and wavelength channels and demonstrate 400GbE transmission over long haul optical fibre infrastructures. Doctor Zhou comments on the future of the field that, “It relentlessly drives for higher performance at lower cost, size and power. As discussed above, the roadmap for ethernet interfaces will continue to scale from 400GbE to 800GbE and beyond. Key to achieving these ambitions will be the development of new advanced modulation formats and FEC technologies. Very significantly, further component integration will be key to developing more efficient manufacturable techniques, thereby reducing size and power consumption, and thereby enabling higher port density and lower cost.”