Optical Fiber Ribbons For the Premises Network, Part I

Part one of a two-part feature describes optical fiber ribbon technology and products and explains why these ribbons are popular today.

By: Herb Congdon, Siecor

Optical fiber ribbons have been used for many years, primarily in single-mode telecommunications and cable television (CATV) applications. Their popularity, coupled with the convergence of telecommunications services and product knowledge, has bred interest for ribbons in other markets.

Part one of this article provides information on ribbon applications and presents some of the reasons why optical fiber ribbons have been so successful. Part two of this article will provide information on using optical fiber ribbons in a private network.

What is an optical fiber ribbon?
An optical fiber ribbon contains two to 24 optical fibers bound side-to-side by a thin layer of acrylate plastic. The fibers in the ribbons do not cross over each other throughout the length of the ribbon and are colored the same as the individual fibers in other cable designs.

Optical ribbon cables are available with single-mode and multimode fibers. The ribbons themselves have some means of identification, usually printed text on the ribbon matrix. Optical ribbon cables contain one or more of these optical fiber ribbons. The majority of optical ribbon cables installed to date have been single-mode. However, multimode fiber ribbons, particularly two-fiber, have become more popular.

Why are ribbons popular elsewhere?
Installing ribbon cables results in substantial reductions in labor costs and less access time at the splice point than installing non-ribbon cables. Additionally, ribbon cable designs have higher available fiber counts (up to 432, for 12-fiber ribbon cables) and greater packing density.

The smaller ribbon cables can be installed in congested rights of way with fewer restrictions due to fill ratio limitations. These same benefits also apply to private network installations.

The ribbon advantage for premises networks
Perhaps more importantly for premises installations, ribbons can be faster and easier to install than the equivalent number of single fibers. The ribbon design takes advantage of technologies such as mass fusion splicing that accommodate multiple fibers simultaneously.

Similarly, it is easier to manage fibers in optical ribbon form than an equivalent number of individual fibers. For example, managing the twelve 12-fiber ribbons in a 144-fiber ribbon cable is much simpler than handling 144 individual fibers.

Mass fusion splicing (splicing several fibers simultaneously) provides time savings when installing optical ribbons. First, it is easier and faster to prepare optical fiber ribbons for splicing than to prepare the equivalent number of individual fibers. Then, a mass fusion splicer can splice up to twelve fibers simultaneously, resulting in a splice time reduction of up to 73%. (Typical values for splicing time are shown in Table 1, below).

Other new products and technologies for ribbons offer similar time and productivity gains for installing connectors. New, multi-fiber designs can connectorize all the fibers in a ribbon and significantly improve the connector density at connection points.

Terminating a two-fiber ribbon with a two-fiber connector takes half the time as installing two single fiber connectors—two fibers are terminated as quickly as one. Also, this same connector takes up only half the panel space as two connectors. In fact, a single ribbon connector can replace twelve single-fiber connectors.

Combining ribbon cables with a single-ferrule, multiple-fiber connector design will yield the most benefits from optical ribbons (See Figure 1, above). This combination installs all of the fibers in the ribbon in the connector simultaneously.

Designs that require fibers to be prepared individually (for example, the SC Duplex) offer fewer benefits when used with ribbons. It is important to understand, however, that these new multiple fiber connector designs do not require ribbons—they are still capable of terminating individual fibers.

Ribbons suited for limited duct space
In situations where the cable size is limited by duct space or fill ratio limitations, the higher packing density (more fibers per cable cross-sectional area) of ribbon cables may provide the best solution. Ribbon cables above 96 fibers will have a smaller overall diameter and minimum bend radius than non-ribbon cable designs of the same fiber count. A similar breakpoint occurs around 36 fibers for inside plant (flame retardant) cables (See Table 2, below, for a comparison of cable diameters and fiber counts).

Optical fiber ribbons and ribbon cables received initial interest from the telcos and CATV providers due to significant installation cost savings because ribbon installations are quicker and easier than those with an equivalent number of individual fibers. In the next installment, the applicability of optical fiber ribbons for the premises network will be discussed, including standards, procedures as well as trade-offs associated with the optical fiber ribbon option.

About the Author
Herb Congdon is a supervisor in Siecor's Applications Engineering Department. He is a registered professional engineer.