The world's fiber networks face a capacity crunch when they reach the Shannon limit and will need to transition to advanced all-optical.

That's the view of Wei Leping, currently director of China Telecom Corp's science and technology committee and a senior MIIT advisor, who has helped design and build the world's largest optical trunk networks.

Speaking at a China optical networking event this week, Wei said a decade ago a number of experts had predicted that the Shannon limit per single fiber would be reached in 2020.

But in Wei's telling, the industry avoided a capacity crisis thanks to a slowdown in demand, with global Internet traffic growth contracting from 40% to around 24%, and network performance gains.

China Telecom was also aided by the provisioning of its backbone network. From 2008 to 2018 its transmission network capacity increased 42% annually, and from 2018 to 2023 it could grow as high as 18% each year, Wei said.

Global Internet traffic is forecast to grow 3.7-fold from 2017 to 2022 at a CAGR of 30%, according to the Cisco VNI.

But Wei said he believes fiber networks will "eventually" face physical and technology limits, and this will be the biggest driver of the migration to all-optical.

He thinks existing technologies, such as WDM and TDM, are unlikely to be able to cope with long-term capacity demands, while emerging tech – like multi-core fiber and OAM – are still in the early stages of development and their economics are not clear.

Wei said China Telecom had been going "relatively fast" in building out what he calls its "all-optical backbone network 2.0."

It is the world's biggest in scale and coverage, with a total length of 220,000km, 470 ROADM nodes, 5,039 lines of 100G and total capacity of 590 Tbit/s.

But all-optical still has some important hurdles to clear, he said.

One is cost. ROADM is key to next-generation optical but it won't be expanding to the edge unless it achieves some economies of scale.

Additionally, the all-optical network must be programmable, requiring tunable settings for speed and wavelength interval and other inputs.

Optical also needs to move towards an open ecosystem, Wei said.

"Starting from the wireless access network, all areas of the network will gradually move towards openness, with interface standardization, software and hardware decoupling, and hardware white box. The all-optical transport network is no exception."

Wei also said the all-optical network needs to reduce restoration time from the current time of a few minutes to ten seconds or less, and it must learn to take advantage of AI.

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— Robert Clark, contributing editor, special to Light Reading