The latest generation of 400G pluggable coherent optics is touted as a network game changer, particularly as they cross from data center interconnect applications to expanded use in the networks of communications services providers. “Standardized pluggable coherent optics, coupled with open line systems and network control, will represent a major change in network design,” said Andrew Schmitt, directing analyst for Cignal AI, via a press release last fall. “This shift will begin in earnest in 2022.”

Such changes should occur first in metro and metro access networks (whose responsibilities, of course, can include data center interconnect requirements). Coupled with other network trends, such as the growing popularity of disaggregated hardware that could provide a home for them, 400G pluggable coherent optics promise to become important tools for communications services providers.

The coming wave

Market analysts believe that the move of 400G coherent pluggables from data center to carrier networks is on the horizon – if not the immediate one. “I think initially, most of the people agree, it will probably be hyperscalers that drive the pluggable modules, the 400ZR,” commented Jimmy Yu, vice president and leader of the optical transport and microwave transmission market research at Dell’Oro Group, during the Lightwave and Broadband Technology Report High Speed Networking 2.0 online conference, held May 4-6, 2021. “We do expect, and we’ve already seen announcements by Telia and Windstream, that they are going to start using 400ZR/ZR+. So we are already going to see it in telecom networks. I’m sure MSOs will also use it. So my expectation is that it’s actually going to be a fairly wide use case.”

“Our understanding of the market suggests that Amazon and Microsoft will be the primary users of 400ZR, at least for the next 3 years. After that, the market may broaden,” added Vladimir Kozlov, founder and CEO of market research firm LightCounting, during the same event. “With ZR+, I think we expect a wider range of customers to begin with, but the ramp may be a bit slower than with 400ZR.”

Nevertheless, as Yu indicated, some network operators have already indicated a willingness to deploy 400G coherent pluggables in their networks. Telia Carrier is starting with router-to-router interconnect applications, pairing the pluggable coherent transceivers with open line systems. "Conventional architectures and technologies built on decades of accumulated complexity and yesterday's truths fall short in helping us keep up with customer demands for more, consistent bandwidth and a high-quality experience,” commented Staffan Göjeryd, CEO at Telia Carrier, at the time the move was announced. “Starting in the metro, standardized coherent pluggable modules are the next natural step in evolving cost structures, efficiency, and scaling capabilities. This follows our global deployments of open optical line-systems and bandwidth-optimized switch-router silicon already powering thousands of 400GbE-capable ports in the network."

Yu sees the use of pluggables for router-to-router interconnect as marking an evolutionary point in both data center and carrier networks. “I do think as we do more 400ZR, we should see more switching and routing become an aggregation point,” he said in May. “Lots of 100GbEs, basically, getting aggregated into 400ZR, as well as the hyperscalers who will probably be moving more to 400GbE interconnects, just doing that as sort of a transport layer out of their data centers.”

Windstream, meanwhile, appears to have its eyes fixed on several applications, including long distance. The service provider reported this past February that it had conducted a trail in which it sent a 400G ZR+ wavelength 1027 km and a 300-Gbps wavelength twice that distance via loopback.

“This record-setting accomplishment by Windstream Wholesale is a game changer for optical networks going forward,” asserted Buddy Bayer, chief network officer at Windstream, when the trial was announced. “Windstream is executing a well-crafted architectural strategy that embraces fundamental design principles of disaggregation, openness, and flexibility. Windstream continues as an early adopter of coherent optical technologies to drive efficient growth and scale of our network and services for our customers. We expect to begin deploying ZR+ coherent pluggable modules in the second half of 2021, a technology that has applicability in as many as 80% of our existing links.”

Based on results such as these, it appears only a matter of time before more communications services providers adopt the new generation of coherent 400G pluggable transceivers.