ANTONY SAVVAS FIBRE CABLE DEVELOPMENT
We are very close to reaching the Shannon Limit in optical transport and are at a point where future network efficiencies are increasingly difficult to obtain.
Jimmy Yu, Dell’Oro Group.
FIBRE EXPANSION “There is still a considerable distance to cover before we reach the limits of optical fibre cable deployment,” says Jitendra Balakrishnan, CTO for optical networks at cable manufacturer STL. Global data consumption is growing rapidly, and this growth is accelerating, and we may be entering an era of even higher data consumption driven by emerging AI applications. “Therefore, we should consider deploying more fibre today than we anticipate we will need, as the cost of fibre in a network represents only around 5% of the total installed cost of a network,” he says Given the demand for higher speeds and capacity in networks, significant research and development is being conducted in various areas of optical fibre technology, says Balakrishnan. The first area of focus is network capacity, which includes modulation formats and the physical attributes of fibre, such as lower loss or multiple cores. Secondly, there is a focus on network architecture, which affects the efficiency and flexibility of a network, and this translates into fibre attributes such as bend insensitivity. Finally, there are the components involving optical fibre, ranging from cable design to interconnect technology, often focused on ease of deployment or the physical footprint. THE SHANNON LIMIT As for the Shannon Limit, as to how many bits of data can be crammed into an optical fibre while still being
look at the physical fibre as a channel, how the Shannon Limit is defined is important. If you consider current, commercially standard, silicon-based single-mode fibre as the channel, with a transmission band of around 750nm, the current Shannon Limit for that band would be something in the order of 1 petabyte for each fibre (depending on length and application). “Current optical transceivers limit the transmission rate within the fibre – not the fibre itself – and currently deployed transceivers are also a contributing factor to the number of multiple strands of fibre in a cable. As optical transceiver technology continues to develop, the transmission capability of the installed base of multi-fibre cables is effectively unlimited,” he maintains. Andrew Lord, senior manager for optical networks R&D at BT, agrees with some of what Yu is saying, when it comes to mitigating limits. “We are definitely approaching the Shannon limit for our high speed transmission core network, with the advent of 400Gbps per wavelength.” Options going forward, says Lord, will include extending to the L-band or simply using multiple parallel fibres, multiple bands (for instance, C + L band), photonic integration, and simplification of the overall multi-layer network infrastructure. While the demand for ever faster and wider data throughput remains, it seems there are still many ways to make sure the fibre being deployed by the optical industry can still cope going forward.
efficiently transported, are we reaching it? Jimmy Yu, an optical transport equipment analyst at Dell’Oro Group, says: “We are very close to reaching the Shannon Limit in optical transport and are at a point where future network efficiencies are increasingly difficult to obtain. This is one reason for the growing interest in increasing the usable spectrum in a fibre beyond the standard C-band (4THz).” Optical equipment manufacturers have been adding super C-band (6THz) and L-band (5THz) to their offerings to enable more spectrum per fibre strand. “In the case of L-band, optical vendors have recently introduced integrated C+L band systems, resulting in over 10THz of spectrum per fibre strand,” says Yu. “Although we have not yet reached the Shannon limit for optical fibre, we are approaching it,” says STL’s Balakrishnan. “The most advanced transmission systems can achieve 1Tbps, while the Shannon limit is several times higher. Therefore, the practical amount of information that can be transmitted on a single optical fibre is affected by many other factors that involve the entire system, not just the fibre. The latest approaches to increasing transmission capacity involve work on modulation formats on the one hand and spatial division multiplexing (SDM) on the other, he says. In SDM, the information is transmitted through spatially separated channels, as in multi- core fibre, or through adding modes, as in few-mode fibres. CommScope’s DiSabato adds: “If you
Massimo DiSabato VP, Strategy & Market Development, Network Cable & Connectivity, CommScope.
Matt Rees CTIO Neos Networks.
Raza Khan Senior Market Manager, Signal Integrity Products, Semtech. group.
Jitendra Balakrishnan CTO optical networks, STL.
Andrew Lord Senior Manager, Optical Networks R&D, BT.
www.opticalconnectionsnews.com
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ISSUE 33 | Q2 2023
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