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Redefining density

Global IP traffic has increased fivefold since 2010 and there is no reason to think that this growth will stop anytime soon. Attempts to keep pace with such capacity demands have seen a dramatic increase in optical cable installations and installed optical fibre counts, causing unprecedented levels of congestion in carrier duct infrastructure. Soon, the large traditional cables installed in these ducts will reach capacity exhaust but, due to the high cost of civil works, many operators will be reluctant to invest in new duct and cable infrastructure. It is obvious that smaller cables with higher fibre counts are needed to provide vital bandwidth and optimise the use of precious duct space, but with so much extra fibre in the network comes another challenge. How can operators physically manage it all without taking on new, expensive central office space?

Smaller cables, bigger possibilities

The key to beating the cyber traffic jam lies in maximising fibre density: in other words packing more fibres into a smaller space – both in terms of cable and duct. In response, vendors have developed miniaturised cables with fibre counts up to 144 fibres that can be up to 50 per cent smaller and 70 per cent lighter than traditional loose tube cables†. This cable miniaturisation naturally yields an increase in fibre density, in turn enabling greater fibre capacity and optimised duct utilisation today and scalable, cost-effective capacity provisioning for the future.

As with loose tube cables, micro cables typically feature 12 coloured fibres per buffer tube, but these tubes are around 40 per cent smaller, making micro cables less robust than traditional loose tube cables. Consequently they must always be deployed in single or bundled microducts for added protection. These mini plastic conduits sub-divide internal duct space into smaller compartments and are light so that, if space allows, a loose microduct can be safely blown or pulled alongside a loose tube cable in an occupied duct. At approximately 12mm in diameter, the largest loose tube cable that can fit into an occupied duct may only provide 96 fibres, but a Ø 12/10mm (outer diameter/inner diameter) microduct can accommodate a micro cable containing as many as 144 fibres, thereby providing up to 50 per cent more fibres to allay total capacity exhaust for longer (see Figure 1).

Figure 1

Excavating roads and pavements can cost as much as €110,000 per kilometre so the motivation to utilise every millimetre of legacy duct space is obvious; but eventually operators will run out of space and will be forced to deploy new duct and cable infrastructure. At this point, they can at least eliminate the need for retrenching for a significant period of time by installing one or more multi-way microduct bundles and fibre-dense micro cables.

The most common duct size in Europe is Ø 40/33mm and the largest typical loose tube cable compatible with it provides 288 fibres. If an operator were to instead deploy a seven-way microduct bundle with Ø 12/10mm microducts, they could install seven 144-fibre micro cables and benefit from 250 per cent more fibres. Moreover, to upgrade beyond the initial 288 fibres with loose tube capacity would require months of retrenching at significant expense, whereas a micro cable upgrade would incur just the cost to purchase and install a new cable into one of five vacant microducts. This process could be completed in a single day and repeated another four times before the operator would have to consider opening up a trench.

With almost five billion connected devices in use in 2015, the pressure on network fibre capacity is only intensifying and, despite the benefits micro cables have brought to the most strained areas of the network, there is already a need for even smaller, even lighter cables with even higher fibre counts. With an eye on the future, some manufacturers have introduced high-density micro cables with fibre counts up to 288 fibres that are up to 60 per cent smaller and 70 per cent lighter than traditional loose tube cables, and up to 20 per cent smaller than standard micro cables.

High-density micro cables use 24 fibres per buffer tube rather than 12. Consequently, fewer tubes are needed to achieve a given fibre count; meaning an operator can choose to maintain cable diameter and increase fibre count, or maintain fibre count and reduce cable diameter, whilst increasing fibre density in both instances. With a typical diameter of approximately 8.0mm, a 216-fibre high-density micro cable offers 50 per cent more fibres in the same space as a 144-fibre standard micro-cable, which translates to 1512 fibres in a seven-way Ø 12/10mm microduct bundle, delivering 425 per cent more fibres than a 288-fibre loose tube cable in a Ø 40/33mm sub-duct (Figure 2).

Figure 2

Previously, high-density micro cables have always featured G.657.A1-rated 200µm fibres for increased macrobend resistance, as necessitated by such tight packing densities. Yet the adoption of such fibres has been deferred by many operators due to worries over splice compatibility with legacy G.652 fibres which have a mode-field diameter (MFD) of 9.2µm versus 8.7µm for G.657 fibres. However, Corning’s new high-density MiniXtend HD cables were developed in conjunction with the latest generation of 200µm fibres, Corning SMF-28 Ultra 200 fibre, which offers a completely unique combination of low loss, 33 per cent better macrobend performance than a G.657.A1 fibre and a 9.2µm MFD in a single, smaller fibre package. These cables offer smaller diameter measurements and greater fibre density than any comparable product in the industry, as well as total compatibility with legacy optical fibre cables.

Managing excess fibre in central offices

A parallel development to the increase in the density of optical fibre cables is the need to optimise the density of fibre management platforms. Optical fibres in an access network are typically routed into a central office or switch centre, so such a dramatic increase in network fibre capacity naturally necessitates an increase in the required number of central office connections. Point-to-point (P2P) architectures will require a like-for-like increase in the number of connection points, while passive optical networks (PON) will see an increase in line with their fibre split ratios. Given that a typical switch centre frame for fibre routing requires 8m² of floor space for every 25,000 port connections, the benefits of micro cables could be dwarfed by incremental real estate costs if new space is required to physically house the extra fibre connections.

Urban central office space can cost as much as €10,000/m² to purchase, so for this reason the industry is developing optical distribution frames that offer higher density in fibre port connection management. Corning’s Centrix platform supports 4,320 LC or 2,880 SC ports per frame, reduces floor space requirements by at least 50 per cent compared to previous products. If four frames are placed back-to-back (1.08m² footprint), the system offers 17,280 LC or 11,520 SC connections per square metre. Moreover, any two of these ports can be cross-connected by a 4m jumper cable meaning a single jumper length can be used ubiquitously in a clear cable routing scheme, without running cable over long distances in overhead trays or coiling slack inside cabinets for shorter connections. This allows an operator to deploy more ports per square metre, easily route more fibre through the same central office without needing to acquire more real estate space and stay ahead of the cyber traffic jam whilst cost-effectively scaling their operations.


Remorseless bandwidth demand is changing the landscape in metro and access networks as unprecedented levels of fibre being driven deeper into the network, leading to critical levels of congestion in carrier ducts. With expensive civil works costs deterring some operators from deploying new infrastructure, the key to beating this ‘cyber traffic jam’ cost-effectively lies in maximising fibre density by packing the maximum number of fibres into the smallest space possible. Recognising this, the industry is developing products that truly redefine fibre density.

Micro-cables offer fibre counts of up to 288 fibres and are up to 60 per cent smaller, 70 per cent lighter than traditional loose tube cables. High-density micro-cables also feature next-generation 200µm optical fibres that combine low loss and G.657.A1 bend performance with a 9.2µm mode-field diameter for total compatibility with legacy G.652.D networks. Finally, the latest fibre distribution platforms offer the ultimate in central office or switching centre density and fibre management, allowing network operators to deal with all of this excess fibre simply and, most importantly, cost-effectively.

Matthew Guinan is a market development analyst for Corning Optical Communications


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