Do optical DACs have a role in future coherent modems?

• A proposed optical digital-to-analogue converter (oDAC) concept offers several system benefits, including better signal performance, higher bit rates and lower power consumption.
• The oDAC design benefits coherent optics but can also be used in direct-detect designs. This article focusses on coherent optics.
• Coherent system vendors are aware of oDAC technology but it is not part of their current roadmaps. 

A 256-QAM constellation using a conventional coherent transmitter (left) and using the oDAC. Note there is no modulator loss (the full area is used) nor any optical warping using the oDAC. Source: Tomkos and Nazarathy.

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Kim Roberts: The 2019 John Tyndall Award winner

A Profile

A conceptualiser, mathematician, furniture maker, prolific inventor, sushi lover, creative spirit, team leader and mentor. These are just some of the descriptors applied to Kim Roberts of Ciena by the people that know him. 

Kim Roberts of Ciena. On the wall are some of his 160 patents while on the screen is an image of a 32-point constellation produced by the WaveLogic Ai coherent modem. Source: Ciena.

Roberts has been awarded the 2019 John Tyndall Award by The Optical Society (OSA) and the IEEE Photonics Society in recognition of his “pioneering contributions to the development of practical coherent communication systems”.

“It is well deserved,” says Seb Savory, who first knew Roberts when they both worked at Nortel and who is now an academic at the University of Cambridge working on joint projects with Ciena. Ciena acquired Nortel in 2010.

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Optical networking: The next 10 years

Feature - Part 2: Optical networking R&D

Predicting the future is a foolhardy endeavour, at best one can make educated guesses.

Ioannis Tomkos is better placed than most to comment on the future course of optical networking. Tomkos, a Fellow of the OSA and the IET at the Athens Information Technology Centre (AIT), is involved in several European research projects that are tackling head-on the challenges set to keep optical engineers busy for the next decade.

“We are reaching the total capacity limit of deployed single-mode, single-core fibre,” says Tomkos. “We can’t just scale capacity because there are limits now to the capacity of point-to-point connections.”

Source: Infinera 

The industry consensus is to develop flexible optical networking techniques that make best use of the existing deployed fibre. These techniques include using spectral super-channels, moving to a flexible grid, and introducing ‘sliceable’ transponders whose total capacity can be split and sent to different locations based on the traffic requirements.

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Briefing: Flexible elastic-bandwidth networks

Vendors and service providers are implementing the first examples of flexible, elastic-bandwidth networks. Infinera and Microsoft detailed one such network at the Layer123 Terabit Optical and Data Networking conference held earlier this year.

Optical networking expert Ioannis Tomkos of the Athens Information Technology Center explains what is flexible, elastic bandwidth.

Part 1: Flexible elastic bandwidth

"We cannot design anymore optical networks assuming that the available fibre capacity is abundant" 

Prof. Tomkos

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The evolution of optical networking

An upcoming issue of the Proceeedings of the IEEE will be dedicated solely to the topic of optical networking. This, says the lead editor, Professor Ioannis Tomkos at the Athens Information Technology Center, is a first in the journal's 100-year history.  The issue, entitled The Evolution of Optical Networking, will be published in either April or May and will have a dozen invited papers. 

One topic that will change the way we think about optical networks is flexible or elastic optical networks.

Professor Ioannis Tomkos

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