ANDY EXTANCE OPTICAL FIBRE
Redefining the limits OF OPTICAL FIBRE
Fundamental physics could pose a threat to the internet’s continued expansion – but new fibre designs could extend the limits, finds Andy Extance.
ANDY EXTANCE
I n seeking to fully utilise its already-installed physical fibre-optic cable infrastructure, the optical communications industry has ingeniously and continuously managed to pack in more bandwidth. Yet current approaches may soon hit a barrier, warns Peter Winzer at Nokia Bell Labs in Crawford Hill, New Jersey: the capacity threshold known as the Shannon Limit. This is the theoretical maximum capacity of a communication channel for a given signal-to- noise ratio. “Modern coherent transponders, and even more so the latest laboratory experiments, are approaching the Shannon Limit very closely,” he told Optical Connections. Consequently, various new optical fibre designs are seeking to postpone the industry’s arrival at this limit. The need for more capacity is well illustrated by British multinational
been developing converged fixed and mobile backhaul networks for several years now,” according to Vodafone’s Head of Transport Eva Rossi. “In our markets we have either Vodafone-owned or third-party fibre,” Rossi said. “Where possible we aim to integrate Vodafone’s fixed and mobile networks in order to maximise synergies.” Vodafone therefore already uses fibre to move enormous amounts of data between cell towers, and its ongoing network evolution will be a key factor in the path to 5G mobile networks, Rossi added. “We are already building networks that are likely to bring some of the benefits of 5G sooner than 2020, when the industry expects 5G services to be rolled out,” she said. MORE BACKBONE REQUIRED The tra c 5G will drive will necessitate high backbone capacities on limited amounts of fibre, Winzer underlined. Nokia Bell Labs’ solution to this is space division multiplexing (SDM), with its current work
Optical communication may soon hit the capacity threshold known as the Shannon Limit. NOKIA BELL LABS
multiple processors into a single chip, rather than putting several processors on a board. Similarly, in the future more integrated fibres, transponders, amplifiers and multiplexers will become necessary throughout optical communications, Winzer said. The Nokia Bell Labs researcher considers current alternative SDM e orts that use hollow-core fibres as of mostly academic interest. They necessitate using light with wavelengths around 2,000nm, not the common telecom wavelengths around 1,500nm. “This is not the way forward, as a shift
involving multi-core and few-mode fibres. SDM simply means integrating parallel transmission paths, just as the commonly used wavelength division multiplexing (WDM) approach integrates several wavelengths, Winzer explained. Although each path still faces the Shannon limit, the capacity of a fibre is multiplied by the number of paths it contains. Winzer considers the multi-core fibre needed to achieve this to be analogous to modern multi-core computer processors. Today electronics manufacturers integrate
telecommunications company Vodafone’s plans. Best known for its cellular telephone networks, Vodafone “has
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| ISSUE 9 | Q2 2017
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