On February 23, CIGNAL AI announced the availability of their latest report, “Coherent at the network edge.” Scott Wilkinson, lead analyst for optical components at Cignal AI, said: “We learned that dedicated QSFP28-based 100ZR modules will fill a central role in the next generation of fiber access networks.” I couldn’t agree more. 

We’ve seen a rapid ramp-up of 400Gbit/s pluggable coherent transceivers in clients’ form factors. It was only a matter of time before operators started to consider using coherent pluggable transceivers for their metro networks and at the optical network edge. 

Are 400G-based coherent plugs efficient for the optical edge?

400Gbit/s pluggable transceivers in QSFP-DD format are revolutionizing optical networks. And not just for point-to-point terascale data center interconnect applications, as initially expected. The adoption of 400Gbit/s ZR+ interfaces with a longer reach and OTN support in carriers’ infrastructure is also ramping up. Moreover, with the 2023 OFC edition just around the corner, there’s a lot of buzz anticipating next-generation coherent transmission technology announcements, enabling pluggable coherent modules with much higher line speeds and capacity-reach efficiency. These advancements in coherent innovation will not only enable higher data rates but also improve the cost efficiency of the optical core.

Can this technology innovation ultimately be applied to the optical network edge? Yes – but not quite as you might expect. Simply driving 400G technology at lower speeds will not be the answer. The optical network edge needs lower power, small form factors and i-Temp capabilities. 

Simply driving 400G technology at lower speeds will not be the answer. The optical network edge needs lower power, small form factors and iTemp capabilities.

Operators are thinking of the best strategy to migrate their optical edge networks. They need to increase transport capacity, but 400Gbit/s is a huge step, not only in terms of capacity but also in terms of cost. The new currency on this part of the network is 100Gbit/s, providing the right connectivity at edge network price levels.

But that’s not all.

The optical network edge has specific needs. For example, consider the growing number of telecom equipment in outdoor deployments, such as optical access nodes or 5G distribution units in street cabinets. This equipment must have a small footprint and low power consumption/dissipation and must be able to work in hardened environments. Given the high number of ports, pluggable modules play a significant role. Every watt counts. Furthermore, pluggables’ form factor must be compatible with existing devices to leverage current infrastructure. But 100Gbit/s coherent pluggable modules based on DSPs developed for 400Gbit/s coherent transmission cannot meet those demands. Why?

Need for purpose-built DSP technology

QSFP28 is one of the most widespread and commonly used form factors for 100Gbit/s applications. However, it has stringent power specifications that cannot be met with DSP technology developed for 400Gbit/s. 100Gbit/s pluggable modules based on 400Gbit/s technology are housed in QSFP-DD or OSFP form factors and have power consumption levels over 10W. That is too large and too power-hungry for the optical edge.

100ZR QSFP28 requires a purpose-built DSP. Adtran (now including ADVA) and Coherent Corp. (formerly II-VI Incorporated) have proven it. They have co-developed the market’s first DSP engineered to meet the stringent QSFP28 power consumption specifications.

100ZR QSFP28 live demo at OFC 2023

The first live demo will take place at the OFC 2023 event. 100ZR QSFP28 coherent pluggable modules will be part of the multi-vendor OFCnet demonstration. 100ZR QSFP28 modules will be integrated into a metro ring network. Using the multi-vendor OFCnet network setup with equipment at the Adtran booth as well as the Coherent Corp. and OFCnet booths, the trial will display 100ZR QSFP28 operating over a metro ring network for the very first time.

If you’re at OFC 2023, please join us at the Adtran booth (2429) to be among the first to see the 100ZR QSFP28 in action.