Make Way for Coherent 400G Pluggables

After attracting significant industry attention during their standards-setting and development phases, coherent 400-Gbps pluggable optics should finally become generally available in the second half of this year. The expectation is that such modules will come from a wide variety of sources, including systems houses. But will consumption match expectation – or, more bluntly, will there be enough demand to satisfy all of the companies who plan on making them available? Predictions vary, but it’s clear the wait to find out will soon be over.

Where to Start

When OIF began work on the 400ZR Implementation Agreement in 2016, data center interconnect was seen as the primary application. Microsoft had validated the concept of plugging transceivers into routers as a way of streamlining router-to-router interconnect, and the belief was that other hyperscalers would adopt the approach at 400G. With the Implementation Agreement published in 2020 and 400ZR and ZR+ (modules that exceed the 120-km transmission reach specified by OIF) transceivers creeping toward general availability, will demand make the devices the dominant data center interconnect option?

400ZR and Open ZR+ modules likely will come in QSFP-DD and OSFP formats, alongside Open ROADM.

“They better be the dominant interconnect technology because we as an industry put so much effort into developing it and suppliers in manufacturing,” commented Vladimir Kozlov, founder and CEO of market research firm LightCounting, when posed the question at the Lightwave and Broadband Technology Report High Speed Networking 2.0 virtual conference in early May of this year. “Our modeling and 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. 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. Certainly the expectations are very high and we are looking forward to seeing some volume shipments in the second half of this year and a lot more in 2022.”

Jimmy Yu, vice president and leader of the optical transport and microwave transmission market research at Dell’Oro Group, also foresees big things for 400ZR/ZR+ in the data center space. But he also expects, as Kozlov implied, that 400G coherent modules will find their way into applications other than data center interconnect. “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,” Yu said during the same event. “However, near term, I’d say the volumes are going to be data center interconnect and over time, as the traditional service providers and MSOs adjust their architecture and figure out where their best positions are to use it, they’ll also incorporate it into their networks.”

Brad Booth, principal hardware engineer in Microsoft’s Azure Hardware and Architecture Group, confirmed his company is ready to transition from 100G coherent pluggables to 400G as part of an overall intra- and inter-data center network upgrade to the higher transmission rate. “That transition we’re hoping to start this year, to start moving into the 400-gig ZR realm of deployment,” he commented. “The nice thing for us is we’re not looking to have to completely rip and replace everything we did at 100 gig. We built the 100 gig with the concept that we would want to upgrade that. And so the way we’ve done the system is, hopefully it’s just a step and repeat – you know, just put in new equipment at each end and the rest of the infrastructure in between stays the same.”

Where Will You Get Them?

The number of optical transceiver vendors positioning themselves to participate in this market is extensive. Kozlov cites such companies as Acacia Communications, (now part of Cisco), Inphi (now part of Marvell), NeoPhotonics, and Fujitsu among the early players, with module suppliers such as II-VI, Innolight, and Lumentum as part of a second wave. However, he also expects at least a few system houses to jump into the game. Ciena and Cisco (via Acacia) are two obvious candidates. Meanwhile, he reports that Nokia likely will develop 400ZR devices for its own use. That’s a lot of competition, which Kozlov says may drive product development strategies. “Some of the suppliers actually even chose not to play in ZR. They’re going with ZR+ just to keep the profitability a bit higher,” he stated.

400ZR+ coherent pluggable transceivers are designed to exceed the 120-km reach specified within the OIF 400ZR Implementation Agreement while otherwise conforming.

While traditional module vendors may not agree, Yu sees the entry of the systems houses into the coherent 400G pluggable module market as a positive trend. “I actually think this is a healthy move for the industry as a whole because it really does offer for the system houses a better way to product differentiate and offer better price points to their customers. So it helps the customers as well,” he explained. “At the end of the day, I think the systems houses that develop or put in that R&D in-house will focus more on how they differentiate at a systems level [via the pluggables], which is going to benefit them.”

What’s Next?

Having finished the 400ZR Implementation Agreement, OIF has now launched work toward an 800G Coherent Implementation Agreement. Interestingly, Booth didn’t immediately endorse the idea, which appears to have been sparked by Google. “Right now, we’re just monitoring the development going on,” he said. “Right now, we’re not looking at 800 gig as mass deployment inside our data centers yet. We’re ingesting 400 gig. 800-gig modules which are 2x400G, we will take those inside. But, making the actual MAC-to-MAC data rate 800 gig, that’s still under investigation as to when we might do that.”

Nevertheless, it seems that if 400ZR and such variants at Open ZR+ and Open ROADM gain the traction anticipated, 800G pluggable optics can’t be too far behind.

Stephen Hardy is editorial director of Lightwave.