With broadband speeds climbing quickly to keep pace with bandwidth requirements for Internet and entertainment video services, builders are "bent" on learning more about fiber-to-the-home (FTTH).
Multi-dwelling unit (MDU) communication lines, in the past, were often copper and/or coaxial communication cables. These bend-sensitive traditional fiber cables were not suitable for mass installation. They would succumb to being bent around tight corners and to compressive forces, like stapling.
Fortunately, builders looking to include FTTH today have much more suitable optical fiber technology with which to work. Small, lightweight cables can be quickly, easily and reliably installed. These cables can be bent, secured, spliced and terminated unlike any other bendable fiber cable.
The Real Value of Bend-Insensitive Fiber Cable
The key attribute of a bendable fiber cable is improved macrobend loss, which is the measure of how much optical power is lost when the fiber is bent in a significant way.
Bend-insensitive fiber cable, then, is fiber cable that can be bent repeatedly around 90 degree corners (and stapled into place) to connect the fiber terminal to the living unit — all without much of any macrobend loss.
Bend-insensitive fiber cable technology greatly simplifies the design engineering and installation of the FTTH network inside new MDUs. Fiber drop cables can now be pulled in and secured in place like copper and coaxial communication drop cables.
Furthermore, the MDU network, which is often interspersed with single-family homes, can be designed much like the outside plant network because indoor fiber cable bend-performance can be anticipated prior to the start of the project.
A design engineer, therefore, no longer needs to scale the serving area back in order to account for unknown losses that might be encountered inside MDUs.
The need for the protection of drop cable inside microduct is no longer necessary. This saves a considerable amount of money related to duct material and the time needed to place the duct. In the past, installation costs alone made legacy fiber installations inside MDUs impractical.
With new bend-insensitive drop cable, there are also fewer opportunities for installation-related issues and callbacks due to macrobend than there were with legacy or less capable fiber cables.
An MDU Fiber Install Walk-Through
To get a better idea of the benefits inherent to bendable fiber, it’s useful to see how it might be employed on a project.
Imagine this:
A feeder fiber cable is fusion-spliced into a fiber distribution hub (FDH). Distribution fiber cable stubs are also fusion-spliced into the FDH. One feeder fiber is cross-connected to 16, 32 or 64 living units via an optical power-splitting module. As a bonus, the FDH requires no electrical power to operate, which eliminates its installation and operational complexity and cost.
The stubbed fiber distribution terminal (FDT) serves as the quick interconnection point to the bend-insensitive fiber drop cable, which is lightweight (yet rugged), so that it can be installed during the construction of the building without needing conduit installed first.
The unique design of a rugged drop cable is such that it cannot be bent beyond its specified minimum bend radius, a mere 5 mm (0.2 in).
In MDU conditions such as these, the fiber drop cable will need to be bent and stapled repeatedly to connect the fiber terminal to the living unit. Not all bendable fiber optic service drops can be bent to a 5 mm (0.2-inch) radius, which corresponds to a hard 90-degree bend. As a result, optical power can be lost at the 90 degree bending points.
The amount of bending loss depends upon the capability of the fiber cable (see sidebar). Macrobend-capable cables, in an installation like this, will maintain low dB values. In a good bendcapable cable, the loss through the bend-insensitive fiber would be no more than 0.1 dB
In any installation, if the received dBm level falls too low because the dB value increased too much, an Internet connection will slow down dramatically or even fail completely due to corrupt packets. Televisions may show “snow” on the analog channels and become pixelated, freeze up or even go out altogether on the digital channels.
Television channel quality is most negatively affected if a fiber cable cannot support multiple 90-degree bends. Stapling can also attenuate the optical power level propagating through an optical fiber, because it places a macrobend force onto the glass strand. One standard staple securing the cable to the wooden framework imparts a force that bends the cable about 15 degrees.
There is only one way to meet escalating bandwidth requirements that has been widely proven — and that is with FTTH networks. In a brand new apartment or condominium building, however, residents will expect to receive top-notch entertainment video display and optical broadband quality for their broadband dollars. To meet these two demands (bandwidth and quality), bend-insensitive fiber cable technology is the answer.
Indeed, it seems that macrobend-capable cables have enabled FTTH to turn the corner and enter into the MDU project.
Mark Turner is marketing manager, consultant engineers, for Corning Cable Systems.