There are two basic cable designs available that are used for designing fiber optic networks in North America. One is loose tube fiber cable, applied in many outside plants, duct, direct-buried applications. Another is tight buffered fiber optic cable, primarily used inside buildings. Before selecting a cable design, there are still many more factors need to consider after determining whether the cables will be used inside or outside.
The modular design of loose tube cables typically holds up to 12 fibers per buffer tube with a maximum per cable fiber count of more than 200 fibers. In a loose-tube cable design, color-coded plastic buffer tubes house and protect optical fibers, also helps in the identification and administration of fibers in the system. A gel filling compound impedes water penetration. Excess fiber length (relative to buffer tube length) insulates fibers from stresses of installation and environmental loading. Loose-tube cables can be all-dielectric or optionally armored.
The cable core, typically surrounded by aramid yarn, is the primary tensile strength member. The outer polyethylene jacket is extruded over the core. If armored is required, a corrugated steel tape is formed around a single jacketed cable with an additional jacket extruded over the armor.
Loose-tube cables typically are used for outside-plant installation in aerial, duct and direct-buried applications. These cables are excellent for outside plant applications since they can be made with the loose tubes filled with water-absorbent powder or gel that withstands high moisture conditions. They also give a more stable transmission under continuous mechanical stress.
Buffer tubes are stranded around a dielectric or steel central member, which serves as an anti-buckling element. With tight-buffered cable designs, the buffering material is in direct contact with the fiber. It has low crush and impact resistance along with a low attenuation change at lower temperatures. The tight-buffered design is well-suited for “jumper cables” that connect outside plant cables to terminal equipment, and also for linking various devices in a premises network. As with loose-tube cables, optical specifications for tight-buffered cables also should include the maximum performance of all fibers over the operating temperature range and life of the cable.
The breakout design and distribution design are the two typical constructions of the tight-buffered cables. The breakout design has an individual jacket for each tight-buffered fiber, and the distribution design has a single jacket protecting all of the tight-buffered fibers. The modular buffer-tube design permits easy drop-off of groups of fibers at intermediate points, without interfering with other protected buffer tubes being routed to other locations.
The tight-buffered design provides a rugged cable structure to protect individual fibers during handling, routing and connectorization. Yarn strength members keep the tensile load away from the fiber. Multi-fiber, tight-buffered cables often are used for intra-building, risers, general building and plenum applications.
There are single-fiber and multi-fiber tight-buffered cables available.
Single-fiber cables have a single fiber strand surrounded by a tight buffer. To terminate loose-tube cables directly into receivers and other active and passive components, single-fiber tight-buffered cables are used as pigtails, patch cords, and jumpers.
Multi-fiber cables have two or more tight-buffer cables that are contained in a common outer jacket. General building, risers, and plenum applications often use multi-fiber, tight-buffered cables. These cables are also used for handling ease and flexibility within buildings and alternative handling and routing.
With these innovative network designs, optical fiber cables have paved the way for easier, more efficient custom cable assembly. Whether for an administrative, medical, or industrial network, fiber optics networking is quickly becoming the number one choice.