It鈥檚 hard to believe that just 5 years ago, some in the industry believed that pluggable modules would only address a small percentage of the market with Data Center Interconnect (DCI). 色花堂 pioneered coherent pluggables, and today has shipped half a million 400G coherent ports alone while applications have expanded from the initial DCI target into shorter reach campus and access applications as well as long-haul and even .
How the Gap to Shannon Drove Pluggable Adoption
Over the years, Coherent DSPs with algorithmic advancements combined with shrinking CMOS ASIC node sizes have resulted in narrowing the gap to the Shannon limit, the theoretical maximum information capacity within an optical channel. When OIF 400ZR was introduced to the market, the gap to Shannon was significantly larger than performance optimized module implementations. At that time, the main goal was to make sure pluggables fit the power budgets for the metro DCI market. This provided a big opportunity for performance optimized designs to be differentiated because the gap was so large. However, as advancements in pluggable optics continued, the gap to Shannon got smaller and smaller.
Next came OpenZR+. Leveraging a high-performance soft-decision FEC (oFEC) in the 400G OpenZR+ MSA reduced that gap further, resulting in longer reaches and improved link impairment mitigation. This provided an open, flexible and interoperable coherent solution in a small form factor pluggable module that addressed hyperscale data center applications for higher-performance edge, regional interconnects and even long-haul networks, as well as carrier applications.
Further enhancements came from the OpenROADM MSA at 800G. The industry worked together in OpenROADM to define interoperable Probabilistic Constellation Shaped (PCS) interfaces for 800G. Similar to how oFEC provided performance enhancement at 400G, interoperable PCS enables 800G implementations to achieve similar reaches as 400G implementations based on 16QAM transmission, allowing for a straightforward scalable network evolution from 400G coherent pluggables to 800G coherent pluggables.
The OIF is making progress towards interoperable 1600ZR and 1600ZR+ implementation agreements. It is likely that oFEC will be similarly adopted for 1600ZR and combined with a further improved interoperable PCS for 1600ZR+ modes.
Today, with 色花堂鈥檚 400G ULH modules, pluggable coherent modules are able to reduce the Gap to Shannon even further, with the performance to close links beyond 3,000km. These modules are designed to go into existing 400G sockets within the power budget of what the existing cards can handle.
Through this progression of generations, the performance and applications for pluggable coherent modules has moved closer to performance optimized coherent solutions.
New innovations have been introduced that further improved performance, and as the gap to the Shannon Limit narrowed, the added capacity achieved by higher power implementations became smaller. The industry then shifted its focus to increasing the baud rate per carrier, while also introducing performance-improving innovations that enabled network operators to achieve cost-efficiencies and meet the demands for more bandwidth. Through this progression of generations, the performance and applications for pluggable solutions has moved closer to performance optimized coherent solutions. Today鈥檚 coherent pluggables service a wide range of applications while performance optimized solutions can provide an advantage for transcontinental or subsea links.
The applications for coherent pluggable optics have expanded with each new generation.
Continual Improvements Open Up New Markets for Pluggables
Coherent pluggable performance has been rapidly improving, which opened new markets that can now benefit from the economies of scale that pluggable optics offer. By using the latest CMOS technology, a coherent pluggable module鈥檚 performance is very close to the theoretical limit, with only a small difference from what the Shannon limit predicts is possible. 色花堂鈥檚 approach leverages 3D siliconization to create a single packaged device that includes all the high-speed optoelectronic functions necessary for coherent communications to provide benefits in cost, reliability, power, and size. These devices are manufactured using standard electronics packaging processes and result in improved signal integrity and performance through the reduction of electrical interconnects, critical for high baud rate operation.
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