Key Advantages of Fiber Optic Ribbon Cable for Data Centers

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Fig. 1.1 Comparison of Standard Ribbon Cables and Ultra High-Fiber Count Cable

Switching to ribbon cable can significantly reduce the time and cost of installing new fiber.

 

Suppose you were responsible for finding the most efficient and cost-effective way to upgrade your data center. Or to future-proof a data center that’s still being planned. The common need in both cases is to equip the facility for an ever-growing amount of data traffic. From a cabling perspective, we propose that the best solution to this need is fiber optic ribbon cable.

Broadly speaking, ribbon cable gives you two ways to save money. In this article, we’ll explain how it does so, and also go over some of the concerns we’ve heard about adopting this technology.

What is ribbon cable? It is a class of fiber optic cable in which the fibers come as conjoined bunches instead of separate, individual strands. These bunches typically have 12 fibers. In its standard format, which was first developed decades ago, the ribbon is completely flat. The ribbon is manufactured with all the fibers aligned across the width of the ribbon on a flat plane. By contrast, a more recent innovation is pliable ribbon fiber. Pliable ribbon fiber is designed with small slits along the length of each ribbon. This makes it possible to roll the ribbon into more tightly packed bundles, which in turn enables the production of cables that contain thousands of fibers per cable. At Sumitomo Electric Lightwave, pliable ribbon goes by the name Freeform Ribbon®.

Advantage #1: more fiber in the same space

There are two major reasons that ribbon cable is more practical than conventional stranded cable, even at fiber counts of 144 fibers. The first is that it allows existing duct space to be used more efficiently. Let’s say you have a 1.5-inch duct in place. The duct can comfortably accommodate cables with a 1-inch diameter, such as a tight-buffered cable with a maximum of 144 fibers or a loose-tube cable with the same number of fibers. Between these two options, the loose-tube cable is noticeably more compact — but it is certainly not more compact than ribbon cable. Why not? Because ribbons occupy less space inside a cable than single fibers do. In other words, a ribbon cable of equivalent size to a loose-tube cable will always have a higher fiber count. In the example seen in Fig. 1.1 (above), the standard ribbon cable contains 50% more fiber than the loose-tube cable. The difference is even more pronounced with Freeform Ribbon, as pliable ribbon can be packed much more densely than standard ribbon.

How the more efficient use of existing duct space translates into cost savings will depend on how much construction can be avoided. Imagine that a project calls for upgrading a cable connection between buildings. One way to implement more fiber is to replace the older cable with a bigger cable of the same type. But if this requires a larger duct, then there will be costs associated with purchasing materials, digging up the old duct, disposing of the old duct, and installing a new duct. The longer the duct, the more expensive the project. Alternatively, more fiber could be implemented by replacing the older cable with a similarly-sized ribbon cable. This method leaves the existing duct untouched. The result would be more fiber, more quickly, with less construction and thus lower overall cost. This logic can also apply in other situations, such as plans to replace indoor cable or projects to build new data centers in a way that allows for future growth in network capacity.

Advantage #2: faster to finish splicing

The other major reason that ribbon cable is more practical than conventional stranded cable is that it takes much less time to splice. For data center owners, this particular feature means faster implementation. For installers, it guarantees higher productivity. Whichever point of view you have, please note that the time and labor savings to be gained are not small — the difference between splicing ribbon vs. splicing single fibers is enormous. This is because it takes the same amount of time to perform fusion splicing on a pair of 12-count ribbon fibers as it does with a pair of single fibers.

In our tests, we observed that it takes an average of 120 seconds (Fig. 1.2)  to complete the sequence of fiber preparation, fiber splicing, and sealing the splice protection sleeve. Let’s apply this figure to our previous scenario of installing 144 fibers. How long would it take to splice this many fibers when using 12-count ribbon cable? With only 12 pairs of ribbon to process in the mass fusion splicer, the total time would be 12 pairs x 120 seconds = 24 minutes. By comparison, when working with pairs of single fibers, total time would be 144 pairs x 120 seconds = 288 minutes (or 4.8 hours). It thus takes almost 92% less time to install ribbon cable. Realizing this kind of efficiency in large projects would result in days, not hours, being saved on finishing this specific task. The efficiency can be gained with either standard ribbon cables or pliable Freeform Ribbon cables.

Fig. 1.2 Typical splicing time, ~120sec, for inline fusion splicing either two single 250µm coated fibers or two 12 fiber ribbons is about the same.

Concerns about switching to ribbon

With such compelling advantages in favor of ribbon cable, what are the concerns about switching to this technology? In general, the concerns we hear from prospective users are about: a) whether it is difficult to learn how to splice ribbon cables, and b) how splice quality compares to single fiber splices.

To address the matter of difficulty, it is fair to say that the learning curve for mass fusion splicing is small. The steps that a technician takes to prepare a single fiber for fusion splicing — strip the fiber, clean it, cleave it, and place it in the splicer — are the same steps taken when preparing ribbon fiber for mass fusion splicing. In other words, mass fusion splicing introduces no additional steps to the splicing process. The only difference is in the tools used: a thermal jacket remover instead of a manual jacket remover; a mass fusion splicer instead of a standard, single-fiber fusion splicer; and, at the end, made-for-ribbon splice protection sleeves.

A related concern about ease of use arises in the context of separating fibers in a ribbon for individual termination. In this case, technicians may see a difference in ribbon fibers from different manufacturers, particularly when comparing the higher-density Freeform Ribbon cable to other commercially available ribbon cables. Freeform Ribbon is made with Sumitomo’s easy peel technology, which allows the matrix material to be easily removed when accessing individual fibers in the ribbon. Freeform Ribbon also easily reverts to its flat ribbon state when removed from the cable, which leads to easier splicing and termination than other pliable ribbon designs.

Turning to the matter of splice quality, continuous improvement in the performance of mass fusion splicers has served to minimize this concern. This can be seen in a comparison of splice loss between a core-alignment fusion splicer and a 12-count ribbon mass fusion splicer (Fig. 1.3). When splicing single mode fiber, the splice losses were 0.02 dB vs. 0.05 dB, respectively. With multimode fiber, the results were 0.01 dB vs. 0.02 dB. In both cases, it is important to note that while the core-alignment fusion splicer does deliver better results, the splice losses from mass fusion splicing are well within the typical allowable limits for this parameter.

 

Fig 1.3 The main difference between splicing a single fiber compared to ribbon fiber is the stripping tool.
 
*Splice loss performance dependent on specific splicer manufacturers and models

Part of a portfolio of solutions

Overall, the dual advantages of ribbon cable make it an extremely practical choice for data center applications. With ribbon cable, you can fit more fiber into existing duct space and you can terminate more fibers in a shorter amount of time. Data center customers have relied on Sumitomo Electric Lightwave for many years to help bring these advantages into their facilities, and in that time we have developed a wide variety of high-fiber-count ribbon cables for outdoor and indoor use. In addition to ribbon cables, today we offer end-to-end solutions that include splice enclosures, cable management products (cabinets, patch panels, ribbon cassettes, etc.), connectivity options (ribbon breakout kits, connectors, pre-terminated cable, etc.), and fusion splicers. We welcome the opportunity to assist you with product selection for data center projects at any scale.

 

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