Tight-buffered cables oftenn are used for intra-building, risers, general building and plenum applications. Tight buffer fiber contains a thick coating of a plastic-type material which is applied directly to the outside of each individual fiber. Loose tube fiber optic cable is typically used for outside-plant installation in aerial, duct and direct-buried applications. Loose tube fiber contains multiple strands of fiber in a single jacket. Since the fibers are “loose” inside the jacket, outside forces are less likely to reach the fibers. This makes it the more durable option of the two.
Loose-tube fiber generally consists of 12 strand of fiber, but can range anywher as low as 6, all the way up to 244 strands. Loose tube cables can be either dielectric or optionally armored. The modular buffer-tube design permits easy drop-off groups of fibers at intermediate points, without interfering with other protected buffer tubes being routed to other locations. The loose tube design also helps in the identification and administration of fibers in the system.
In a loose tube cable design, color-coded plastic buffer tubes house and protect optical fibers. An optional gel filling compound impedes water penetration. Excess fiber length (relative to buffer tube length) insulates fibers from stresses of installation and environmental loading. Buffer tubes are stranded around a dielectric or steel central member, which serves as an anti-buckling element.
The cable core, typically uses aramid yarn, as the primary tensile strength member. The outer polyethylene jacket is extruded over the core. If armoring is required, a corrugated steel tape is formed around a single jacketed cable with an additional jacket extruded over the armor.
Single fiber tight buffered cables are used as pigtails, optical patch cord or fiber jumpers to terminate loose tube cables directly into opto-electronic transmitters, receivers and other active and passive components. Multi fiber tight buffered cables also are available and are used primarily for alternative routing and handling flexibility and ease within buildings. With tight buffered cable designs, the buffering material is in direct contact with the fiber. This design is suited for “jumper cables” which connect outside plant cables to terminal equipment, and also for linking various devices in a premises network.
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.
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. Averages should not be acceptable.