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Breaking the Optical Glass Ceiling – What comes after 400G/600G?

By Heidi Adams, IHS Market

Successive rounds of optical innovation and investment have delivered higher capacity networks with significantly decreased cost-per-bit transmitted.  In the near future, as we approach Shannon’s limit, gains will become more incremental, and the cost-per-bit of added capacity will become more linear. As an industry, will we be able to break through the optical glass ceiling to achieve terabit optical networks?

This year is shaping up to be the year of 400G/600G for coherent optical applications. Ciena began shipping WaveLogic Ai-enabled 400G-capable ports in volume in the fourth quarter of 2017, and announcements at OFC 2018 from Coriant, Fujitsu, Cisco and other vendors indicate that additional 400G/600G-capable products will become available later this year. Nokia also announced its next-generation coherent digital signal processor (DSP), the PSE-3, which employs probabilistic constellation shaping (PCS) to support 400G/600G wavelengths. However what is most interesting here is Nokia’s positioning. With PCS, Nokia claims it has effectively reached the bounds of Shannon’s limit. If this is the case, what’s next and how will we get to 1 terabit (1T) and beyond?

Moving to higher-order modulation schemes, such as 1024 or 2048 QAM -- or to faster symbol rates of 100 Gbaud and beyond -- offers diminishing returns, in terms of capacity gains. Programmable FEC, Nyquist subcarriers, super-channel implementations and other techniques can improve spectral efficiency on a fiber, but they are not the breakthrough tools that will enable the desired order-of-magnitude jump to 1T wavelengths. Alternate paths forward must be explored.

More products with L-band support will become available, and advanced fiber -- including few-mode, multi-core and coupled core -- will gain more industry interest. Space-division multiplexing (SDM) could also begin to move out of research and into commercial applications. There is always the blunt-force approach of laying more parallel fiber and employing some form of link-aggregation technique to hash traffic across multiple physical fibers, while treating the grouping as a single entity from a management perspective.  Or work to increase utilization on fiber links by leveraging Software Defined Networking (SDN)-enabled resource optimization tools, machine learning algorithms, and eventually, more automated networking.

When all is said and done, the end goal is economic. Agile companies must address growing capacity demand in the most cost-efficient manner possible.  As we touch on the limits set by Shannon’s Theorem, perhaps a 1T wavelength is not the only end goal. Breaking through the optical glass ceiling will require new and creative approaches. Expect to see at least part of the solution arrive in the form of more holistic network-centric approaches to moving more bits more efficiently.

Heidi Adams is the Senior Research Director, IP & Optical Networks at IHS Markit


Posted: 11 March 2018 by Heidi Adams, IHS Market | with 0 comments

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